I Want Some Suggestions On Potential Problem Sources 1987 Corvette

[Grumpy]

I've got a 1987 corvette here, in the shop,that had a blown head gasket I repaired,
the engines got good compression, and it runs decently when first started and will do so unless its engine is turned off,
this is intermittent problem, making it a bit harder to isolate,
the engine does not cut out or stall if left running,
that engine starts right up, if cold (sitting over night )
instantly crank up and run, its got good oil pressure, 37-39 psi cold, and does not drop below 30 psi at idle.
good fuel pressure consistently 40-42 psi and,
while I'm not overly impressed ignition spark at the spark plugs,
noid lights show injector harness is functional,
the tps is correctly set at .54 volts, IAC functions as designed.
it will start up and run fine until its turned off the first 2-3 times, in a row,
ignition timing is set at 8 degrees advanced and increases as expected if the engine rpms are increased,
the valves are properly adjusted,the firing orders verified the plugs are gaped at .043 ,
and show the engine runs decently, the infrared temp gun does not show any cylinder firing issues,
there are no blown electrical fuses. (Im begining to think this might be VATS related,)

you can let it run for 15 seconds- or 3 minutes or so, or for 5-7 minutes each time, its started,
and turn it off and it will restart instantly, the first 2-to sometimes 3 times,
but after the 3rd to 4th consecutive re-try or restart,
it spins over but won,t start?
theres no vacuum leaks and I don,t think its likely to be heat related,
as I can start the engine and turn it off about every 10 seconds and by the 4th time the no start condition starts,
and within only 40 seconds total run time its barely started to warm up
trouble code indicates a code #33 ( MAF sensor too much flow)
but the volt meter indicates the MAF is functional ?)
now I will track this down and report what I find,
so this might be helpful to others once I isolate and test and find the cause,
and I will as soon as I get someone too start the car, control the throttle and help watch gauges,
and let me use gauges and meters under the hood ,
but I,m curious if anyone else has run into this?
problems like this can be rather fun to sort out!
but at times it really helps to have two people as you can,t be two places at once!
theres nothing complicated, its all just isolate and test, and thinking logically,
and of course having the correct tools and a shop manual, and experience, helps
I'm sure its something like a defective sensor,
but at times having a friend that can start the car and play with the throttle,
while you verify sensor function, spark, fuel and oil pressure under the hood,
makes diagnosing the problem source much easier

https://www.the12volt.com/relays/relaydiagrams.asp (read)

85 and 87a -> Ground

86 -> Power

30 -> Output

-30 = constant [positive (+)] power (usually wired directly to car battery)
-85 = coil ground (wired to the negative (-) battery terminal or any grounded metal panel in the car)
-86 = coil power (wired to the control source. could be a switch, or it could be the car's IGN or ACC circuit.)
-87 = switched [positive (+)] power output. (when the relay coil is powered, lead/pin 87 is connected to lead/pin 30)
-87a = [on 5 lead/pin relays only] this lead/pin is connected to lead/pin 30 when the coil is NOT powered.

these charts are for the 1985-89 vette cooling fans

# Check fan fuses in the underhood fuse/relay panel
# Check fan relays (same location). Aside from getting out any electrical equipment to test the relay, you can swap it with another one (such as the fog lamp relay) and test for function. See if the relay works for the fog lamps and/or the swapped-in relay makes your fans work. Nearly all the relays in the panel are the same, except for maybe the ABS relay.
# You can jumper two pins on the DLC that should cause the fans to come on. 1993-1994 cars with the 12 pin DLC can jumper pins A and B. On a 1993, that is the same way that you would retrieve trouble codes from the ecm. The 1994 won't give you any codes, but the fans will engage. 1995-1997 uses pins 5 and 6 on the 16 pin DLC to initiate what is called "field service enable mode". That will cause the fans to come on and operate most sensors for sanity checking. After placing the jumper on the correct pins, turn the key to ON (don't start). If the fans work after jumpering the DLC, your PCM is capable of operating the fans and all fan wiring/relays should be ok.
# Deeper problems can be solved through testing and using the wiring schematic.


~Fans don't come on except when the a/c or SES is on~

~Temp gauge continues to rise with no automatic fan operation~


# With a scan tool, check to see what temp the PCM is seeing from the sensor in the water pump. Make sure you are aware of the temps the fans come on (stated in the beginning of this article). If the temp it sees is incorrectly low, it won't know to turn the fans on. Another possibility is that the temp is really ok, but the gauge is reading wrong. That is why you need to use the scan tool to see and compare the readings. Info on testing wiring and sensor can be found here.
# If that looks ok, then your PCM may have issues. You could always try resetting the PCM by pulling the PCM BAT fuse for about 30 seconds.

viewtopic.php?f=70&t=3504&p=9220#p9220
Testing the ECT (Engine Temperature) Sensors and Connections

THE DIAGRAM ABOVE HAS THE CORRECT WIRE COLORS

Pro tip before starting - Label your relays Relay 1, Relay 2, and Relay 3 according to the wiring diagram (your first post) and what your physical relays represent. Even if its just a sticky note. Get it all straight and stick to the same annotation while you troubleshoot.

You'll need a multimeter than can measure DC voltage and continuity:

Remove all three relays so you're only dealing with the sockets

DC Voltage tests:
1. Confirm 12V between the socket for pin 85 and the negative battery terminal on all 3 relay sockets
2. Confirm 12v between the socket for pin 30 and the negative battery terminal on relay sockets 1 and 2

Continuity tests:
1. Confirm continuity with the end of the dark green wire and the socket for pin 86 for relay 1
2. Confirm continuity with the end of the dark blue wire and the socket for pin 86 for relay 2 AND relay 3.
3. Confirm continuity between the socket for pin 87 for relay 1 and side B of the left cooling fan connector
4. Confirm continuity between side A of the left cooling fan connector and side B of the right cooling fanconnector AND the socket for pin 87 for relay #2.
5. Confirm continuity between the socket for pin 87 for relay #3 and Negative Battery Terminal
6. Confirm continuity between side A of the right cooling connector and Negative Battery Terminal.

Do the steps in order and use the negative battery terminal for your connection when I specify to. Verifying at the negative battery terminal will ensure you're circuit is making a good connection to the chassis ground. If it doesn't make it all the way back to the battery, it's a crap ground and testing it my way will reveal the problem




ECT Temperature vs. Resistance Values

ºC ºF Ohms
100 212 177
90 194 241
80 176 332
70 158 467
60 140 667
50 122 973
45 113 1188
40 104 1459
35 95 1802
30 86 2238
25 77 2796
20 68 3520
15 59 4450
10 50 5670
5 41 7280
0 32 9420
-5 23 12300
-10 14 16180
-15 5 21450
-20 -4 28680
-30 -22 52700
-40 -40 100700

Use a Digital Volt Meter (DVM) set to ohms to measure resistance. Note: Use a high impedance meter (at least 10 megohm) when dealing with the PCM. Most modern DVMs will do, but your old analog meter can damage the PCM. It is also a good idea to get a " reference" from the meter you are working with. With the DVM on the ohms scale, touch the two meter leads together and note the ohm reading. It may not always be perfectly zero, but may be within a tenth or two. Now when you take an ohm reading, you will know what the meter will show when there is really no resistance.

* The sensor in the head has only one terminal. This sensor is for the temperature indicator on the dashboard. Place one test lead on the sensor terminal and the other on a known good ground. Compare the reading to the table. If your car is cold from sitting overnight, the reading should be close to ambient temperature.
* The sensor in the water pump has two terminals. This sensor is for the temperature input to the PCM. Place a test lead on each of the sensor terminals to take the reading. (When reading resistance, it does not matter which lead goes to which terminal)

If the sensor seems to be ok, you may also need to test at the harness connector for proper lead conditions. Use your test meter set on the dc voltage scale to do this. You will need the key in the RUN position, but don't have to start the car.

* For the one lead connector at the head, place the red test lead on the connector terminal and the black test lead to a known good ground. With the key ON, you should read battery voltage (+12vdc or close to it). You can also ground the lead and see if the gauge in the car deflects to full hot.
o If you get no voltage, switch the meter to ohms to see if the lead is grounded.
o No voltage or no ground mean that the lead is open.
o If the gauge is at full hot all the tme, the lead is grounded back toward the gauge. It could be possible for the lead to be pinched and grounded toward the gauge and broken and open back toward the sensor (like in the case of the wire getting caught somewhere during some major engine work). Physically tracing the wire from the sensor into the harness should locate the problem.
* The two lead connector at the water pump has a black (ground) lead and a PCM +5vdc power lead (probably yellow). Place the black meter test lead to black connector lead and the red meter test lead to the other connector lead (yellow on my 1995). You should read +5vdc because this is monitoring voltage being supplied from the PCM.
* If you get no reading:
o Test the yellow lead by placing the DVM red lead on it and the DVM black lead to ground. A +5vdc reading will indicate the lead is ok.
+ If you get no voltage, switch the meter to ohms to see if the lead is grounded.
+ No voltage or no ground mean that the lead is open.
o You can test the black connector lead by using the ohms scale on the DVM. Place the DVM black lead to ground. Place the DVM red lead to the black lead of the connector. If the lead is ok, you will get an ohm reading close to zero. If you get no reading or a very high one, the lead is open or partially open.
* OBD-I DTCs 14 and 15 or OBD-II DTCs P0117 and P0118 are typically associated with problems the PCM sees with the sensors or circuits.

Footnote: If you ever have to test the IAT, it operates the same as the two lead coolant sensor. The same temp vs. resistance table above is applicable to the IAT, as well as the +5vdc lead and ground wire at the harness connector.


any thoughts gentlemen?

be aware the electrical grounds 104-105,106,107 must be checked and firmly connected to the engine

a factory shop manual and a v.o.m. meter come in handy for testing!
http://www.chevythunder.com/Flow chart index.htm

the factory installed, tuned port high ohms injectors, should read between about 11 ohms and 13 ohms resistance

http://garage.grumpysperformance.co...ouble-shooting-rebuilding-hei-ignitions.2798/
potentially related threads, these links hold a great deal of info

http://garage.grumpysperformance.com/index.php?threads/c4-c5-corvette-trouble-codes.2697/#post-91077

http://garage.grumpysperformance.com/index.php?threads/gm-tpi-stalling-diagnosis.15194/#post-86992

http://garage.grumpysperformance.com/index.php?threads/maf-burn-off-relay-info.661/#post-908

http://garage.grumpysperformance.com/index.php?threads/testing-1985-89-m-a-f-sensor.1475/#post-3325

http://garage.grumpysperformance.co...oven-facts-if-your-in-doubt.13051/#post-84695

http://garage.grumpysperformance.co...-won-t-start-intermittently.14212/#post-72158

http://garage.grumpysperformance.co...urrent-flow-grounds-and-more.3504/#post-54624

http://garage.grumpysperformance.co...start-right-back-up-and-run.10739/#post-46893

http://garage.grumpysperformance.co...-idles-and-sometimes-stalls.10688/#post-46308

http://garage.grumpysperformance.co...m-with-how-your-c4-corvette-runs-badly.15212/

http://garage.grumpysperformance.com/index.php?threads/1989-corvette-shows-a-trouble-code-33.15594/

 

[T-Test]

It could be the ignition module in the distributor or possibly the ignition switch itself which would relay back to the VATS. I personally would do away with the VATS and install another anti theft system. Too complicated to diagnose and repair/reset.

 

[Grumpy]

https://www.hotrodhandbooks.com.au/eBooks/TPI/TPI On Line-04-1.html

TPI Components
Sensors and Actuators

The complete TPI System relies on data from various sensors (eg Oxygen Sensor) so that engine performance and efficiency is kept at a constant optimum. The system causes actuators (eg Fuel Injectors, IAC Motor etc) to react accordingly. For example, if the Oxygen Sensor, located in the exhaust manifold, senses an incorrect Oxygen level, an electrical signal is sent to the ECM. The ECM prcesses this information and sends a command to the Fuel Injection System to change the air/fuel mixture. This constant activityensures a predetermined, ideal air/fuel ration is maintained, no matter what the conditions.

The following table lists the TPI Systems Sensors and Actuators.

Table 2 - Sensors, Actuators
Sensor
Actuator
Non ECM Devices
Exhaust Oxygen
Fuel Injector
Crankase Vent (PCV)
Throttle Position
Idle Air Control Motor
Engine Temp. Sensor (Overheat Gauge)
Coolant Temperature
Fuel Pump Relay
Oil Pressure Sensor (Gauge)
Vehicle Speed
Trans. Converter Clutch
Oil Pressure Switch (Fuel Pump)
Detonation
Electronic Spark Control module
Cold Start Valve
Mass Air Flow
Engine Fan
Cold Start Thermal Time Switch
Manifold Air Temperature
Air Control (divert) Solenoid
A/C Pressure Cycling Switch
A/C Pressure
Air Switching (Cat. Conv.) solonoid

Fan Override
EGR Solonoid


Fuel Vapour Canister Solenoid


Manual Trans. Overdrive



Injector Assemblies
Corvette and Camaro/Firebird TPI systems also differ in that the fuel line connections exit on different sides of the engine. The Corvette systems lines exit near the front of the right cylinder head and face forward (Figure 5 Page 10), whereas the Camaro/Firebird systems connections exit toward the front of the left cylinder head and face toward the left side of the engine (Figure 6 Page 10).

The Corvettes fuel line position is compatible with accessory mounting combinations which mount the alternator on the left side of the engine. The position of the Camaro/Firebird systems fuel lines work well with combinations which mount the alternator on the front of the right cylinder head, the power steering pump low on the left front corner of the block, the air-conditioning compressor on the left cylinder head and utilize individual V-belt drives for each accessory.

The Corvette system is normally used with a serpentine belt drive. 1988 and later Camaro/Firebird TPI systems also use a serpentine belt drive, but the accessories are positioned differently to the Corvette units.

Also, Corvette engines with aluminium cylinder heads have a unique Exhaust Gas Recirculation (EGR) plumbing arrangement because of the lack of exhaust crossover passages in the aluminium cylinder heads. The lack of these crossover passages require the routing of exhaust gases to the intake manifold via a tube that connects to the right hand exhaust manifold.

The TPI side runners or, as they are more commonly referred to, Ram Tubes, are interchangeable between different years and models, with the understanding that there are specific left and right side units and also, that 89 and later systems are not equipped for a cold start valve. Therefore, the left side ram tube assembly does not have the required mounting provision for the cold start valve assembly, and the 89 and later intake manifolds do not have the proper internal passages to allow the 86-88 cold start system to function properly.

All intake manifolds interchange to any Small Block Chevrolet but, as mentioned, 89 and later manifolds have no provision for a cold start valve assembly. Intake manifolds, used on 87 and later engines with cast iron heads, have the two center intake manifold bolt hold-down holes drilled at a different angle than earlier engines. These manifolds can be used on the early engines if the bolt holes in question are machined, or otherwise opened up, to allow the mounting bolts to be installed.

All of the fasteners used on the TPI system utilize metric threads and most of the bolts used to assemble the individual components of the TPI system use TORX type heads. The intake manifold is held to the cylinder heads with standard 3/8" 16 USS bolts. However, these too have a TORX type head. The intake manifold hold-down bolts require the use of a #T45 TORX driver and the bolts which hold the balance of the TPI system together utilize a #T40 TORX driver. In addition, some of the TPI assembly hardware occasionally utilize bolts with 10mm, 13mm and 15mm size hex heads.

All intake plenum assemblies are interchangeable. Corvettes use an aluminium plenum extension (GM #10108425), which extends over the distributor, that can be used to replace the easily broken, plastic unit used on the Camaro/Firebird systems.

All the throttle body assemblies are interchangeable. However the 89 units use a different attachment point for the throttle cable, which can create additional problems with the throttle linkage hook-up in most non-OEM applications.

If your prior knowledge of TPI systems is limited to some quick looks under the hoods of various Corvettes and Camaros, the names and acronyms of the following parts may seem foreign, and unusual, to you but their functions are really quite familiar. Whether an engine is equipped with a carburetor or fuel injection, it still needs the correct mixture of air and fuel to run. The functions of most of the following components allows them to work together to accomplish this end. For example, a carburetor has a choke mechanism to enrich the fuel mixture when starting a cold engine. Chevrolets TPI uses a 9th injector and an engine temperature sensor to perform the same function. In the following paragraphs, we will attempt to explain the various functions of the major components of the TPI system and, where appropriate, how to accommodate them to a non-OEM application.

 

[Grumpy]

Computer Command Control (CCC)

The Computer Command Control (CCC) system comprises the Electronic Control Module (ECM) and information sensors which monitor various engine functions and returns data to the ECM. The data is processed by the ECM and, if necessary, the ECM issues commands to change the operating parameters of the engine to optimise performance and economy at all times.

Electronic Control Module
The ECM, commonly referred to as the "brain" of the system is, in fact, a computer and is capable of making over 600,000 commands per second. In later year systems, it is also referred to as the Engine Control Module (ECM) since some vehicles have an additional computer unit known as a Body Control Module (BCM), which is involved in the control of various non-engine or drive train functions. The Body Control Modules are not covered in this book, and should not be confused with Throttle Body Fuel Injection Systems.

The ECM receives information about the engines operating conditions from various sensors and then calculates the optimum spark timing and fuel mixture according to preprogrammed values. The ECM controls the fuel mixture by varying the duration of time that the 8 injector solenoid valves are open. This time period is referred to as the pulse length and is measured in milliseconds. General Motors smart ECMs have memory and learning ability and can remember changes that produce peak performance. The ECM is calibrated to a specific vehicle and engine combination by a removable PROM (Programmable Read Only Memory) which, in the 86 through 89 ECMs, is part of a removable insert referred to as a MEM-CAL (Memory Calibrator). The MEM-CAL contains the calibrations needed for a specific vehicle/engine combination, as well as the back-up fuel control circuitry required should the ECM unit become damaged or faulty. This back-up fuel circuitry is contained in a chip similar to the PROM, referred to as the CAL-PAK, and is also contained within the MEM-CAL assembly. The CAL-PAK is programmed to allow fuel delivery in the event of a PROM or ECM malfunction. This back-up fuel control capability is commonly referred to as the Limp-Mode.

Our information shows that, when installing TPI systems in Hot Rods, Jaguars, Four Wheel Drive and other non-standard swaps, the most practical place to mount the ECM is underneath the passengers seat. In this location it simplifies the initial wiring procedure and, later on, allows easy access for MEM-CAL or ECM replacement, if necessary, or other diagnostic and trouble-shooting purposes. Depending on the particular vehicle into which you are installing the TPI system, this location may or may not work for your application.

ALDL Connector
The Assembly Line Diagnostic Link (ALDL, also known as the ALCL or Assembly Line Communications Link) has terminals which are used in the assembly plant to check that the engine is operating properly before it is shipped. This connector also allows a technician to troubleshoot the system by attaching what is known as a SCAN tool to the ALDL connector in order to access all important information relative to the operation of the various control circuits within the ECM. These SCAN tools are available from most tool retailers such as Snap-On, MAC, etc. Prices start around $US400. Most of these units can be described as hand-held in terms of size. One of the more common units, marketed by the OTC Division of the Sealed Power Corporation and sold under the Monitor 2000 trade name, measures 33/4" (9.525cm) x 71/2" (19.05cm), is 11/2" (3.86cm) thick, and weighs only 1 lb 2 oz (0.96Kg). In addition to having Light Emitting Diode (LED) or Liquid Crystal Display (LCD) screens, which display real time information while the engine is running, most SCANtools can be attached to printers for recording data and can even be interfaced (with special software) to your home Personal Computer.

There is, in fact, a recently released software package that comes equipped with the proper cables to allow direct connection between the ALDL connector and your PC. It takes the place of the SCAN tool itself, and uses the PC to display the information that would normally be displayed in the readouts of the SCAN tool. Because of its portability, a lap-top computer is recommended with this combination. However, it can be used with a standard desk-top PC. Through the use of specific plug-in modules, these SCAN tools can be adapted to almost any year or model vehicle which uses an ECM controlled engine. In the GM applications, the ALDL connector is usually installed underneath the dash where it can be easily accessed by a technician. We have found it simpler, and more expedient to install it near the ECM underneath the passengers seat, as this puts it out of view while still keeping it accessible for diagnostic purposes, in addition to simplifying the re-wiring process.

Mass Air Flow Sensor
The MAF sensor measures the amount of air passing through the engine. Chevrolets Tuned Port Injection system uses a hot wire type MAF sensor that determines air flow by measuring the current required to maintain a heated wire at a constant temperature as intake air passes over the wire. The MAF sensor is the chief compensating feature in Chevrolets TPI. This unit must be mounted between the air cleaner assembly and the TPI throttle body.

The MAF sensor is the one piece of the TPI system that seems to give the most problems, as far as positioning and mounting, in almost all non-factory applications. Interviews with Engineers from Hot Rod Circles have informed us that by using 85-89 Pontiac Firebird air intake components, ie, air cleaner, air box, and ducting, we can end up with a "factory" look for this usually troublesome area of TPI installations. While this procedure adds some additional work, it results in a professional looking installation.

Obviously, the particular clearance problems dictated by the specific installation you are working with will determine the location of the MAF sensor and its attendant ducting. The farthest we have seen the factory mount the MAF from the throttle body is approximately 15 inches (38cm). We have always tried to maintain this as a maximum distance when repositioning the MAF sensor. Placing the MAF sensor farther away than this may create some driveability problems!

The MAF is also the sensor that is the most likely part of the entire system to be missing or damaged. Be sure to obtain one in your package deal when purchasing either a TPI unit or a complete engine with a TPI installed, as they are in excess of $US300 when purchased new from a GM dealer. Also, be sure that the MAF sensor has a 5-pin connector. We have anecdotal evidence of people attending numerous swap meets encountering quite a few unscrupulous vendors trying to sell "complete" TPI units with a V-6 3-pin type MAF sensor. They are very close in size and appearance to the V-8 MAF sensor unit, but will absolutely not work with the V-8 system! In addition to the 5pin connector, the correct MAF sensor has I.D. cast into it, indicating that it is manufactured by BOSCH of Germany, whereas the 3-pin 6-cylinder type unit has I.D. indicating it is manufactured by the A.C. Delco Division of GM.

Oxygen Sensor
The Exhaust Oxygen Sensor (EOS) is mounted in the exhaust manifold where it can monitor the oxygen content of the exhaust gas stream. It does this by measuring the amount of oxygen molecules in the exhaust.

This sensor allows the system to function in the feedback or closed loop mode. The oxygen sensor improves driveability by providing input to the ECM, causing the ECM to adjust the fuel injector pulse-width settings to produce an ideal 14.7:1 air/fuel ratio. When the oxygen sensor is removed, or disabled, the TPI system operates in its open loop mode at pre-programmed settings.

In the open loop mode the ECM will compensate for changes in engine and air temperature, as determined by its preset calibrations, but cannot fine-tune the fuel mixture. In way of reiterating the need for soldered connections and care in eliminating corrosion from the various connections in the TPI system, the total functional variation that the oxygen sensor circuit measures is from about 0.1 volt for a lean condition, to about 1.0 volt for a rich condition, thus spanning a total voltage variation of approximately nine-tenths of one volt!!! In the factory application the oxygen sensor is mounted in the exhaust manifold. If your level of fabrication experience is such, it is possible to remove the oxygen sensor boss from the late model factory manifold and install it in the earlier Corvette-style Rams-Horn type exhaust manifolds that work on many Street Rod applications. It is also possible to obtain an after-market weld-in type of boss that can be installed in the exhaust down-pipe, just below the exhaust manifold, or header.

Should you decide to fabricate your own mounting boss, the threads on the oxygen sensor are metric, 18mm / 1.50 to be exact, and the area around the threaded hole must be flat, since the sensor uses a sealing washer. It is important that, if the oxygen sensor cannot be mounted in the exhaust manifold, it must be mounted in the down-pipe as close as possible to the manifold since, for the system to go closed loop, the oxygen sensor must reach an operating temperature of 600°F.

Fuel Injector Assembly
The system uses 8 primary injectors wired and fused in 2 groups of 4. One group is for cylinders 1, 3, 5, and 7, and the other for 2, 4, 6, and 8, referred to as odd and even injectors. GM wires and fuses four of these injectors together, and when we install the system, we duplicate the fusing on the outside chance that, should one injector short out and blow the fuse for that bank, the injectors on the other bank will continue to function, allowing the engine to continue running.

Commenting on the reliability of these units: we have never heard of anyone experiencing an injector failure, nor have we found any GM technicians who have. The biggest problem when these injection systems were first introduced, was clogged injector nozzles. This has been just about solved by fuel treatments such as those manufactured by Pro-Ma Systems, which introduces not only a very efficient detergent into the fuel system, but a top end lubricant to counter the drying effects of unleaded petrol and a surfactant to break down surface tension of water inherent in all fuel tanks, and allow the water to pass harmlessly through the fuel system, and into the combustion chamber.

Injectors are manufactured by Rochester, MULTEC, Lucas, and Bosch and have different fuel flow rates between the 305 cu. in. and 350 cu. in. engines, and different rates between injectors provided by one manufacturer or another for the same application. According to GM, the injectors should be retained with their specific engines and not interchanged. While we agree that the injectors should be matched to their specific engine, if at all possible, we have found that if they are interchanged in sets, ie, 305 cu. in. injectors installed in 350 cu. in. engines, they will work quite adequately, due to the adjustability engineered into the MAF controlled TPI systems. If there is any noticeable difference, it will only appear under full throttle maximum output conditions. In the real world, if engine rpm is kept below 4500, we have not seen any noticeable difference in their performance or mileage by using 305 cu. in. injectors in 350 cu. in. or even larger displacement engines. We would caution, however, that the injectors only be switched in sets, ie, do not mix 305 cu. in. and 350 cu. in. injectors in the same engine, since the system has no way of determining fuel delivery rates for individual cylinders.

Cold Start Injector
This 9th injector is located between cylinders #3 and #5, on the left side of the intake manifold, on 85 through 88 units. The 1989 and later injector systems are calibrated differently to compensate for the lack of a cold start injector. Para 31. page 10 refers. The cold start injector enriches the fuel mixture for up to 8 seconds during cold cranking. It is wired directly into the starter solenoid circuit, is controlled by the Thermal Time Sensor, and operates ONLY when the starter is cranking the engine over.

Thermal Time Sensor
This temperature sensitive sensor activates the cold start injector when cranking a cold engine, but is not used in 89 systems. The time period during which it allows the cold start injector to inject additional fuel into the engine is based, inversely, on the temperature of the engine below 95°F, ie, above 95°F there is no additional fuel injected by the cold start injector. As the temperature drops, the time period during which the cold start injector is engaged (to inject extra fuel) is increased to a maximum of 8 seconds at -5°F. This sensor is threaded into the front of the intake manifold, in the area below the thermostat housing. It uses a 2-wire connector with a spring clip very similar to the type used on the fuel injectors.

Throttle Body
The Throttle Body attaches the Cruise Control, Accelerator and Transmission Throttle Valve Cables, and connects the Mass Air Flow Sesor via the Air Intake Duct. The Throttle Body also houses the Throttle Position Sensor and Idle Air Control valve, described in the following paragraphs.

Throttle Position Sensor
The Throttle Position Sensor (TPS) informs the ECM if the throttle blades are closed, or whether the throttle blades are open and, if open, how far they are open.

It also sends information on the rate of change in the throttle opening. This unit is mounted on the right side of the throttle body assembly, with 2 TORX head machine screws, has a 3-wire connector and is actuated by a tang on the throttle shaft that engages a lever on the TPS. Basically, the TPS is a potentiometer which informs the ECM with a voltage reading proportional to throttle opening, from 0.54 volts, at idle, to approximately 5 volts at full throttle. This is the only sensor in the TPI system that can be manually adjusted. It should be adjusted with the throttle plates closed, using a digital voltmeter or a SCAN tool for a reading of 0.54 ± 0.08 volts. (See "Final Adjustments", Para on Page .)

Idle Air Control
The Idle Air Control (IAC) device uses a small stepper motor which operates an adjustable tapered valve. The valve maintains engine idle speed at closed throttle by controlling the amount of air allowed to bypass the closed throttle valves in the twin bores of the throttle body.

The engines idle speed is determined by the calibration in the MEM-CAL, and is not mechanically adjustable beyond setting, what is referred to as base idle, which in most stock applications is approximately 500 rpm. This base idle is set by removing the 4-wire connector from the IAC unit, to eliminate ECM control, and adjusting the throttle plate stop screw, (refer Figure 18 Page 20) which is on the top left side of the throttle body assembly. The IAC unit is on the right side of the throttle body below, and slightly forward of, the TPS sensor. (See "Final Adjustments" on Page .)

Coolant Temperature Sensor
This sensor, which is mounted alongside the Thermal Time Sensor (Para 55.), at the front of the intake manifold (below the thermostat housing), is a thermistor which sends engine temperature information to the ECM which enriches or leans the fuel mixture, as required, by predetermined calibrations stored in the ECM. It utilizes a 2-wire connector.

CAUTION!
Handle the coolant temperature sensor with care. Damage to this sensor will adversely effect the operation of the entire fuel injection system.

Manifold Air Temperature Sensor
The Manifold Air Temperature (MAT) sensor is located in a threaded boss on the underside of the TPI plenum. Identical (same GM part #) to the Coolant Temperature Sensor (CTS, Figure 21 ), this thermistor sends information to the ECM on changes in inlet air temperature for which the ECM delays EGR until manifold temperature reaches 40° F enriches, or leans, the fuel mixture according to predetermined calibrations stored in the ECM. It also uses a 2-wire connector similar to the one used on the Coolant Temperature Sensor.

Electronic Spark Timing
All spark timing is controlled by the ECM. Electronic Spark Timing is the control of ignition advance by the ECM, and comprises the following components;

• Distributor;
• Electronic Spark Control (ESC) module; and
• Knock Sensor.

Distributor
The distributors used with TPI injector units are very similar to the HEl-type distributors used on electronically controlled throttle-body injected, or carburetted V-8 engines, in that they have no internal advance mechanisms or vacuum advance control canisters.

The distributor supplies reference signals to the ECM for spark timing and information on engine rpm. The 4-pin connector plug, with which these distributors are connected to the basic wiring harness, while similar in appearance, is different enough to prevent a non-TPI distributor from plugging into a TPI harness without changing the plug end. However, the color codes are the same and the non-TPI distributors will work with the TPI system.

There may be some minor internal electronic differences between the two, but, in the real world, we have found no problem using the non-TPI units in conjunction with the TPI systems.

1975 THROUGH '80 HEI DISTRIBUTORS WITH AN EXTERNAL VACUUM ADVANCE UNIT WILL NOT WORK IN CONJUNCTION WITH A TPI SYSTEM.
This is because the ECM requires a specific rpm input signal from the distributor. While all Corvettes use the large integral coil type HEI distributor, 1987 and later Camaro/Firebird units use a new type of distributor quite similar in size to the earlier point and condenser-type distributors that GM used prior to 1974. While smaller than the previous HEI-type distributors, it is still considered a HEI distributor, the main difference from the earlier HEI distributors being the use of an externally mounted coil. In most cases, you will use the distributor that comes with your TPI unit. We prefer, whenever possible, to use the Corvette style, larger HEI with the integral coil simply because it cleans up the installation and eliminates the coil, coil mounting bracket, and extra wiring.

ANY DISTRIBUTOR USED ON THE '87 AND LATER ROLLER LIFTER-TYPE CAMSHAFT EQUIPPED ENGINES MUST USE A DISTRIBUTOR GEAR DESIGNED TO BE COMPATIBLE WITH THE BILLET STEEL CAMSHAFT USED IN THESE ENGINES.
GM #10456413 is the correct gear for use on the earlier HEI large integral coil-type distributor. GM #10495062 is the correct gear to use on the later style, smaller HEI distributor that use a separate remotely mounted coil. If the distributor drive gear is not changed, the steel cam will chew up the stock iron distributor gear normally used on the earlier pre-roller cam distributors!

Knock Sensor
The knock sensor, located on the lower right side of the block, detects vibrations that are the acoustic signature of detonation and informs the Electronic Spark Control module (following) which, in turn, directs the ECM to retard the timing in an attempt to eliminate the detonation.

The combined effect of these two units can retard the ignition timing up to 20 degrees to compensate for bad fuel, high engine temperature, or any other combination of factors that produce detonation. This unit is normally mounted on the right side of the engine, in the coolant drain hole, just above the oil pan rail in front of the starter motor.

Electronic Spark Control (ESC) Module
The Electronic Spark Control (ESC) has the capability of retarding the spark timing by up to 20 degrees when the knock sensor detects detonation.

This unit, which is slightly smaller and thinner than a pack of cigarettes and has a 5-pin wiring connector, is mounted by two small bolts, in most GM applications, in a group with the 3 relays that are used for the fuel pump and the MAF power and burn-off circuitry, on the cowl, on the right side of the evaporator blower or inner fender. We recommend mounting this unit along with the ECM, (eg underneath the passenger seat) as it again simplifies the wiring process and eliminates clutter in the under hood area.

Electronic Spark Timing operation
To optimise engine performance, fuel economy and emissions, the ECM controls distributor spark advance (ignition timing) with the EST system.

The ECM receives a reference pulse from the distributor, indicating engine RPM and crankshaft position. The ECM then sets the correct spark advance by way of the EST reference pulse to the distributor.

 

[Grumpy]

Relays
There are three ECM controlled relays which are an integral part of the TPI system.

• Fuel Pump Relay;
• Mass Air Flow Power Relay; and
• Mass Air Flow Burn-off Relay.

Fuel Pump Relay
The fuel pump relay is controlled by the ECM and acts as a remote switch to route power to the electric fuel pump. A relay is necessary in this application because most high pressure fuel pumps can draw up to approximately 10 amps of current. The fuel pump relay is backed up by an oil pressure activated switch which maintains +12 volts at the fuel pump power terminal as long as the engine has oil pressure. This will allow the vehicle to start and continue running in the event of a fuel pump relay or partial ECM failure. This oil pressure activated, fuel pump control switch is mounted (depending on the year and model), either in a threaded port on the left side of the engine block (just above the oil filter), or in conjunction with the oil pressure gauge sending unit in a fitting behind, and to the left of, the distributor assembly.

The first indication that the fuel pump relay has failed and that the back-up switch has taken over fuel pump operation, would be extended cranking time before the engine eventually starts, accompanied by an illuminated Check Engine/Service Engine Soon light.

Mass Air Flow Power and Burn-off Relays
The other 2 relays are the MAF power relay, and the MAF burn-off relay. These twin relays supply current:

• through the MAF Power Relay, to provide power to the MAF sensor when the engine is running, and
• through the Burn-off Relay, to burn-off contaminants on the MAF sensors hot wire when the engine is shut off.

In GM installations these 3 relays are usually mounted in a group with the ESC module on the cowl, or inner fender panel. In our applications, we suggest mounting these relays along with the ESC module in the area of the ECM (eg underneath the passengers seat), to eliminate engine compartment clutter and ease the wiring process.

 

[Grumpy]

very helpful related videos

https://www.thirdgen.org/injectorswap/

https://www.thirdgen.org/tpimod2/

 

[Grumpy]

https://www.amazon.com/ALLOSUN-EM27...ocphy=9012039&hvtargid=pla-492764925793&psc=1

https://www.amazon.com/Electronic-F...ocphy=9012039&hvtargid=pla-375685424093&psc=1

https://www.robietherobot.com/storm/fuelinjectorguide.htm

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

https://www.chevyhardcore.com/tech-...-injector-identification-and-cross-reference/

https://www.ebay.com/p/All-Sun-EM27...MIo7OtlcbL4wIVDSsMCh393wbOEAQYAiABEgJl3_D_BwE

 

[Grumpy]

UNPLUG the harness from the injector, put your V.O.M. meter on OHMS and put the leads accross the two connectors ON THE INJECTOR ,it should read about 11-16 OHMS in most cases, a few are designed to read up to 19 ohms, or as low as 9 ohms ,if its out of that range by a wide margin ITS MORE THAN LIKELY DEFFECTIVE, checking the OHMS reading as a first step will frequently detect a deffective injector, naturally useing your trouble codes , a shop manual and a fuel pressure gauge won,t hurt and a shop scope , or engine analyzing software with a read out to your laptop computer helps and can further isolate the problem, at IDLE speeds placing a finger tip on the side of the injector will usuially allow you to feel it (CLICKING) adding a couple cans of injector cleaner and about a pint of MARVEL MYSTERY OIL to a full tank of fuel can sometimes free a sticky injector that partly clogged, but don,t do it frequantly as its very hard on the CATS and O2 SENSORS if done constantly

the factory installed, tuned port high ohms injectors, should read between about 11 ohms and 13 ohms resistance


notice, the injector resistance is usually stated in the description

Brand: ACCEL
Product Line: ACCEL Fuel Injectors
Part Type: Fuel Injectors
Part Number: ACC-150826
Injector Advertised Flow Rate (lbs/hr): 26 lbs./hr.
Injector Advertised Flow Rate (cc/min): 269.0cc/min
Injector Impedance: 14.4 ohms
Driver Type: 12 V saturated circuit
Overall Height (in): 2.880 in.
Seat to Seat Height (in): 2.270 in.
Manifold O-Ring Outside Diameter (in): 0.573 in.
Fuel Rail O-Ring Outside Diameter (in): 0.574 in.
Outside Diameter (in): 0.943 in.
Injector Plug Style: Bosch/Amp-style
Wiring Harness Included: No
O-Rings Included: Yes
Quantity:




MORE INJECTOR INFO

Like all electrical devices, injectors have an internal resistance to the flow of electricity. The amount of resistance is measured in Ohms, or impedance. The higher the number, the more the resistance. Injectors are either high impedance or low impedance. It's crucial to get the proper type. While high and low impedance injectors may look identical on the outside and fit the same, if they are the wrong type they can fry your ECU, injector resistor pack, or other expensive parts. High impedance injectors are sometimes called "peak and hold" injectors, while the low impedance injectors are often called "saturated injectors." Make sure you get the right type. If you're not sure what you've got, you can check the resistance of your injector with a DMM (digital multi meter) set to measure Ohms. Saturated injectors have a resistance between 10-18 ohms and peak-hold injectors have a resistance around 2-6 ohms.

your corvette was designed to use the 10-18 ohm rated injectors

basic fuel injector test
(pull your trouble codes and check battery voltage ,alternator output and ignition spark first)

(BTW it rarely hurts to drain old fuel thats over 4 months old and replace the cars fuel filter, then add two different brands of fuel injection cleaner and 6 oz of marvel mystery oil to as full tank of fresh high test gas to the car if its been sitting un-used for very long before you start testing for fuel injection related issues

now Ill assume your battery reads over 12 volts and the starter works, and easily spins the engine
the first step
find the fuel rail shrader valve and remove the cap and connect the fuel pressure gauge
if you turn on the ignition key to get the dash and accessories to light up but don,t start the engine,the fuel pump,
should briefly run to pressurize the fuel rail to about 38psi-42 psi,
this should stay at this pressure level for at least 5 minutes minimum, if it drops slowly your fuel rail is leaking fuel.
now the fuel pressure regulator may be defective or leaking, or in very rare cases the fuel pump may be defective ,
but the most likely cause is a fuel injector(s) stuck in the open position.
next pull the injector harness,

off a single injector at a time, press the wire bar to release the clip, retention, then pull it up and off, the noid light plugs into the harness,
use the spare injector pig tail

on the now disconnected injector ,connect the multi meter on ohms setting and it should read 11-13 ohms injector on each injector tested.
if it reads under 9 ohms or over 20 ohms its a defective injector
now use a couple 3 ft long test leads connect one too one of the pig tail test leads
https://www.walmart.com/ip/Uxcell-2...-Clips-Test-Jumper-Wire-1-5m-2-Color/45588242

and to 12 volts, connect the other pig tail lead too a different test lead and watch the fuel pressure gauge,with the key out of the ignition , you should have 38-42 psi of fuel rail pressure, watch carefully while you tap the second test lead to ground (the plenum or alternator case works) the fuel pressure should drop as you tap the ground pig tail lead, this verifies the injector function at least partially, if you don,t see the pressure drop the injectors not allowing fuel flow through it and should be replaced.
after you complete each injector test , turn the ignition key on, to re-pressurize the fuel trail and reconnect the harness to the previously tested injector,
repeat the noid light and pig-tail function fuel pressure test on each of the other injectors individually.

youll need a fuel pressure gauge and multi meter

it helps if you have a spare fuel injector pig-tail for testing

having a NOID light injector harness tester wont hurt either
https://www.harborfreight.com/11-piece-noid-light-and-iac-tester-set-97959.html

on the TPI and LT1 efi and many other EFI intakes,
theres a shrader valve,
that can be easily accessed to check fuel rail pressure,
dealing in facts you verify is always preferable.

GM part number for the complete fuel rail o-ring kit is 17111696

if your TPI FUEL PRESSURE REGULATOR DIAPHRAGM LEAKS youll find it difficult or impossible to be starting your car

heres a link to the correct o-rings they are light blue
NAPA sells them at times
all the o-rings on the fuel rails and injectors need to be dipped in thin oil so they insert and slide into place with less friction, this tends to greatly reduce the chance of the o-rings ripping, and yes you need the correct o-rings that fit correctly to begin with if you expect the rings to seal correctly
http://tpiparts.net/inc/sdetail/10950/300

17113544 - Injector Seals
17111696 - O-Ring Kit
22514722 - Fuel Inlet O-Ring
22516256 - Fuel Inlet O-Ring

if you have a cylinder or two not functioning correctly or a injector thats barely functional, an infrared temp gun checking the exhaust port temps will generally allow you to find and isolate its location as it will be usually be running at a lower average temperature,
infrared thermometers are a very useful tool to track down issues with tuning, or mal functioning sensors , without verified facts your guessing.
this is the most consistently accurate I.R temp gun I've used for testing[/img]

http://www.testequipmentdepot.com/e...1100200223789&utm_content=All Extech Products
INFRARED TEMP GUN
Wide temperature range from -58 to 1832°F (-50 to 1000°C)
any time that your dealing with a potential temperature issue or a trouble issue where , knowing the exact temperature vs what a gauge might say, it helps to have a handy and accurate infrared temp gun handy to locate and confirm heat, levels.

http://garage.grumpysperformance.co...dding-a-fuel-pressure-gauge.15264/#post-88472

http://garage.grumpysperformance.co...njection-at-start-up-problem.7309/#post-24862

http://garage.grumpysperformance.co...oven-facts-if-your-in-doubt.13051/#post-84695

http://garage.grumpysperformance.com/index.php?threads/tpi-fuel-pressure-issue.10385/#post-42943

http://garage.grumpysperformance.co...-system-trouble-shooting-flow-chart-info.596/

http://garage.grumpysperformance.com/index.php?threads/diagnoseing-tpi-lt1-problems.1241/

http://garage.grumpysperformance.co...m-with-how-your-c4-corvette-runs-badly.15212/

http://garage.grumpysperformance.com/index.php?threads/re-manufactured-maf-bad-code-34.15752/

http://garage.grumpysperformance.com/index.php?threads/code-45-problem.15753/

http://garage.grumpysperformance.com/index.php?threads/gm-tpi-stalling-diagnosis.15194/#post-86991
http://users.erols.com/srweiss/tableifc.htm

btw if the C4 vettes HEI ignition is still having that issue with intermittent ignition spark,
Id suggest replacing the ignition module, distributor cap, and coil as they are rather frequently the cause.

http://garage.grumpysperformance.co...istributor-ignition-modules.16056/#post-96896

http://garage.grumpysperformance.com/index.php?threads/replacing-the-hei.952/#post-93417

https://www.rockauto.com/en/catalog...1,ignition,ignition+control+module+(icm),7172

https://www.rockauto.com/en/catalog...350cid+v8,1041231,ignition,ignition+coil,7060

https://www.rockauto.com/en/catalog...0cid+v8,1041231,ignition,distributor+cap,7120

http://garage.grumpysperformance.com/index.php?threads/adjusting-your-tps-and-iac.168/#post-89805

http://garage.grumpysperformance.co...oblem-sources-1987-corvette.15596/#post-93277

http://garage.grumpysperformance.com/index.php?threads/c4-c5-corvette-trouble-codes.2697/#post-91077

http://garage.grumpysperformance.co...blem-with-my-87-c-4-corvette.5055/#post-89786

 

[Grumpy]

HISTORY OF GM PORT INJECTION

http://www.fuelinjection.com/techs.html

The first production TUNED PORT INJECTION (TPI) appeared on General Motors vehicles in 1985. The GM vehicles built with these systems were Corvette, Pontiac Firebird & Trans AM, and the Chevrolet Camaro. These systems according to the manufacturer rendered up to 30 % improvement in Horsepower, torque and economy over carbureted systems, Independent laboratories conducted numerous tests on the TPI systems and indicated these claims were conservative and that increases of up to 35% in these three areas are attainable.


The 350/5.7L engines from the factory went from 205 HP (1984 Corvette/ crossfire injection) to 245 HP with the addition of TPI. The only differences were the addition of the TPI (1985) and improvements in the valve train (1987). Note that this is a 20% improvement over another proven form of fuel injection.


Several modifications have been made to the TPI system introduced in 1985. The 1985 system used a GM Part #1226870 ECM and had a Mass Air Flow (MAF) sensor and a MAFS module to control the power and burn off functions for the MAFS. In 1986 two relays replaced the MAFS module and the Electronic Control Module (ECM) was changed to a GM part #1227165. In 1989 the cold start injector was deleted from the system. The primary injectors were used for cold starts via a fuel enrichment program in the newer EPROM calibrators. In 1990 GM introduced the speed density system. In essence the MAFS was replaced with a Manifold Air Pressure (MAP) Sensor. This system uses an ECM GM Part #1227727 for the Corvette.


Another fuel system was introduced in 1992 called Central Port Injection (CPI) and appeared first on the 4.3L (W) L35 Engine. This system is the equivalent of TPI for the V6 and will increase horsepower and torque by a factor of 20% over TBI. A 30 % increase in horsepower, torque and fuel economy is seen over carburetion.


The LT1 was also introduced in 92, as the basic engine in the Corvette. It appeared in the Firebird, Z28 (F Body Cars), Caprice, Buick and Cadillac in 93. 1993 was the last year for EPROM's in these cars. Opti-Spark also made its entry on the LT1 engine in 92.


In 94, OBDII or EEPROM, computers were first used in the Corvette and F Body Cars. This was the 1st year for Sequential port Injection in these cars.


In 96 the LT4 appeared in the manual trans Corvette, it is rated at 330 HP and 340 lb ft torque. It looks the same as the LT1, however the heads and valve train have been modified. The valves are larger 2.00 Int / 1.55 Exh from 1.94/1.50. Air passages are larger to enhance volumetric efficiency, hollow valve stems, aluminum roller rocker arms and stronger valve springs have also been added. The camshaft has more lift and a slight overlap at the end of the combustion cycle eliminating the need for EGR. The compression ratio is (Premium Gas Only) 10.8:1 compared to the 10.4:1 LT1. This engine makes 330HPat 5800 RPM and 330 lb ft Torque at 4500 RPM.


We flowed the heads on both the LT1 and LT4. LT1's flowed 195 CFM compared to 240 CFM for the LT4.


Ported LT1's also flow 240 CFM. Porting the LT4 will render 272 CFM.


For 96 all Chevrolet engines are Sequential Port and are equipped with On Board Diagnostics Phase II (OBDII) PCM's. Sequential Central Port Injection is a standard on the 4.3L/4300, 5.0L/5000 L30, 5.7L/5700L31, and 7.4L/7400 L29 engines. What's nice about all this? They will fit the old engines, but heads would also have to be changed on the 4300, 5000 and 5700 engines.


Retrofit kits are available from FIS. For Example, Sequential Tuned Port Injection or Sequential Central Port, both systems are available from FIS.


Other Technological mods include Cam Sensor / Crank Pos Sensors in lieu of distributors. EEPROM Computers, Vortec Heads, Mass Air Flow Sensor, Roller Cams / Roller hydraulic lifters come with all engines. Retrofit kits are now available, from FIS, for Sequential Port Injection which will fit the SB, BB and the 90 degree V6 GM Engines.

Electronic Control Module (ECM)
The ECM's provided with the original equipment MPFI systems are indicated below:

Y=Corvette F=Camaro, Firebird, Trans-AM CK=GMC, CHEV trks

Power train Control Module (PCM)

The PCM is a programmable computer and does not contain a EPROM or calibrator as did its predecessor. The PCM contains a Electronically Eraseable Programmable Read Only Memory (EEPROM). This unit must be programmed before being placed in service. These Units can be re- programmed for any engine / transmission combination. All of these units are Sequential Port Fuel Injection (SEFI).

While each of these ECM's/PCM's will provide excellent performance for the Port and TPI systems, they are not interchangeable. That is a 1227165 will not plug in to a 1226870 harness and operate. The wiring for these systems is not interchangeable, without modifying the wiring harness. The LT1 PCM is not compatible with the earlier ECM's due to significant changes in the distributors of these engines.


The CK truck engines use a crank shaft sensor and camshaft position sensor to provide timing information to the engine.

CALIBRATORS

The calibrator is a Programmable Read Only Memory (PROM) Chip which is installed in the ECM. It is this device that provides specific information for the ECM and allows for different timing characteristics, and injector pulse width for the 5.0L / 5.7L engines. A Calpak, a separate chip on the Calibrator Modules, normally provides the information to the ECM for rear axle gear ratio on pre 90 models. Information for the vehicle Anti Theft system, auto / manual transmission, and emission control system, typically resides in the EPROM. To allow for the various Engines, transmission, gear ratio combinations and to meet national, international and state standards for emissions, a wide variety of these Calibrators are available from GM. After 1987 some calibrators incorporate a vehicle anti theft system (VATS). The ECM will not fire the injectors until it receives the proper signal from the VATS module. The 1985 TPI calibration is contained in an EPROM (Erasable Programmable Read Only Memory) and is a 32K chip. The 1986-89 ECM contains a 128K EPROM, 90-92 ECM's use a 256K EPROM. The 94 Plus EEPROM is even larger. The factory ECM/PCM has a Learning capability which allows it to make corrections for minor variations in the fuel system to improve performance and drivability. There are two learning features. The Integrator and Block Learn (I and BL) and Block Learn Memory (BLM) cell. The I and BL feature is normal with a value of around 128. If this value is higher than 128, it indicates that the ECM is adding fuel to the base fuel calculation because the system is running lean, a value lower than 128 indicates that the ECM is taking out fuel because the system is running rich. The integrator is a short term corrective action while the BLM is along term correction. The BLM value will change if the integrator has seen a condition which lasts for a longer period of time. There are from two to sixteen different cells which the ECM modifies, depending on RPM, airflow or manifold air pressure and other conditions such as AC "ON" or "OFF", etc. The ECM learns how much adjustment is required in each cell, retains it in memory, and applies these adjustments when the engine operates in that cell or RPM - Load Range. These features of the OEM ECM allow the system to adjust itself AUTOMATICALLY to your engine and assure peak performance for stock and other than stock engines. When the vehicle power is disconnected for repair or to clear diagnostic codes, the learning process has to begin all over again. To TEACH the ECM, drive the vehicle at operating temperature with moderate acceleration and idle conditions. Performance Calibrations typically change the parameters for fuel flow, fuel cut-off and spark advance-timing and will allow increased fuel flow and modify the spark advance curves during rapid acceleration.


WHAT THE ECM - PCM DOES: The 1985-1988 TPI system utilizes the following sensors and devices to control the engine: Mass Air Flow Sensor, Manifold Air Temperature, Coolant Temperature, Oxygen Sensor, Throttle Position Sensor, Cold Start Switch, Cold Start Injector Fuel Injectors, Idle Air Control Valve, Distributor Electric Spark Timing, (Module in distributor TPI) Electric Spark Control, Module and Knock Sensor.

click this link

Wayback Machine

web.archive.org

 

[Grumpy]

When the starter is engaged and the coolant temperature is less than 100 deg F. The cold start injector provides a spray of fuel, of 8 seconds duration max, to each cylinder via an air distribution system built into the intake manifold. If the engine temperature is greater than 100 deg F, the cold start injector is disabled by the cold start switch. Upon startup the ECM utilizes information in the calibrator to establish the initial pulse rate for the injectors and the engine starts. At this time the engine is operating in open loop mode and will continue to do so until the engine warms up. After the warm up period the ECM scans the sensors, if all sensors are operating and within their proper range, the engine then goes into closed loop operation. This means that the sensors are dynamically controlling the engine. In the event the information received is higher or lower than the normal range, a code will set in the ECM, and the Check Engine or Service Engine Soon light will come "on". The ECM receives information on air flow, engine temperature, air temperature, exhaust gas oxygen content and throttle position. This information is used to calculate the proper pulse width for the injectors and fires the injectors for the calculated period. This procedure is repeated continuously in very rapid sequence to maintain the optimum fuel air ratio. The electronic spark control components provide maximum advance, if engine knock is detected the spark is automatically retarded. This too, is a continuous process. It should be noted that the following components are MATCHED for optimum performance; Distributor - EST module, ESC module, knock sensor and ECM calibrator. These components are not interchangeable between 5.0L - 5.7L engines. 5.7L components referenced are recommended for 327 - 400 CID engines. 5.0L components are recommended for 265- 305 CID engines.


In 1989 the cold start injector was deleted. The calibrator provides a wider pulse width on startup to provide a richer mixture for a cold engine. All other features are the same. In 1990 the MAF was replaced with the MAP sensor, in 94 the MAF returned with a MAP sensor. The1990-92 TPI system still operates the same except that Manifold Air Pressure is used to calculate injector pulse width as opposed to airflow. The 1990-94 TPI - LT1 system also uses a more sophisticated VATS system to disable the injectors. A resistor is embedded in the ignition key. The resistance is read by a VATS module (Camaro, Firebird and Trans AM) or a Command Control Module (CCM) for the corvette. If the key is the right resistance a signal is sent to the ECM enabling the injector circuit. If the sequence or the resistance is not correct, the engine will not start.


The PCM introduced in the 1994 Corvette, Camaro and Firebirds for the LT1 engine accomplishes the same functions as the earlier models in much the same way, but there are some significant differences. The 94 and up LT1 is a sequential port fuel injection system. The injectors are fired in coordination with the opening of the intake valve. The distributor and electrical spark timing system, now referred to as "Opti-Spark Control", has an optical sensor which counts light pulses through a perforated disc in the distributor. There is NO timing adjustment for the LT1. The Mass Air flow sensor is back in 94 and is one of the primary sensors for fuel control. The MAP sensor is a backup for the mass air flow sensor. All other sensors are the same except that the TPS is no longer adjustable. The only adjustment is idle control, and this too is factory set.


The 96 OBDII engines all use EEPROM computers making Chip technology something from the past. These PCM's and VCM's have the ability to determine a cylinder misfire and will even tell you which cylinder misfired. Opti-Spark is now the standard ignition system on 5.7L LT1-LT4 engines. For 96 a combination crankshaft position sensor and cam shaft position sensor perform the timing functions on all the 4.3L, 5.0L 5.7L and the 7.4L engines.


The LS1 is now the new small block appearing in the Corvette in 97 and the Camaro / Firebird in 98. The LS1 does not have a distributor. The PCM uses the information from the crank and camshaft position sensors to calculate timing and fires the individual ignition coils.

One thing is CLEAR, Innovation is alive at GM.

CASTINGS

The 1985-86 intake manifolds will fit the older small block heads without modification. In 1987 and up, the heads were designed with vertical bolt taps for the two center bolts on both sides of the intake manifold. With a little drilling the newer manifolds will fit the older style heads. The intake manifolds are therefore interchangeable for all small engines. The plenum is interchangeable for all model years thru 1990. The 1990 and up have tapped holes for the mounting of a MAP sensor (right rear of plenum). The throttle body is different on 90 and later models, modifications can be made to the plenum to use the 90+ Throttle Body by drilling a hole in the front of the plenum. Intake tubes (runners) are interchangeable for all model years; however the left intake tube through 1988 has a mounting for the cold start injector, for 89 and up this mounting is deleted.


NOTE: Throttlebodies 85-88 are the same and must be matched to plenums 85-88. To work properly on 90 and up plenums a hole (1/2") must be drilled, between the intake openings where the throttle body mounts, to allow for passage of idle air from the IACV to the plenum. 89 and up throttlebodies will work on earlier plenums without modifications.


LT1 Throttlebodies


The 93 Throttlebody on the LT1 engine is similar to the TPI, but does not have an EGR port. The throttle linkage lever is also slightly different. The 93 throttlebody does have a stud for the trans TVS cable. The 94 and up units do not. If you are using a 700R4 / Turbo 350 transmission, a stud will have to be mounted for the TVS cable.


FUEL RAILS

Stamped - F=Camaro, Pontiac Y=Corvette


TPI Fuel Rails


The TPI fuel rails have a few differences. If the left side fuel rail has a fitting at the end close to the firewall it is from a 1985-88system. The fitting is for connection of the cold start injector fuel line. The left side fuel rail is stamped at the factory to identify same with the engine. The Fuel Rail Identification Table above will assist you in identifying your system as a 5.0L / 5.7L and the injectors furnished with those systems.

LT1 / LT4 Fuel Rails


The 93 Fuel rails do not have a crossover tube at the front of the intake, nor does the intake have provisions for the crossover. The crossover setup is on all 94-97 LT1 engines. The fuel supply and return lines are on the left side of Camaro, Caprice, Cadillac and Buick engines. The Corvette has both the fuel lines on the right hand side.

LS1 Fuel Rails


The 97 LS1 has provisions for a supply and return line. The 98 and up fuel rails have a supply line only. The fuel system of the 98 LS1 has a regulator built in to the fuel pump return assembly the return line is from a "T" fitting between the fuel filter and the engine.

 

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Distributors

All 85-86 systems used a GM HEI distributor. The connector for the distributor is keyed differently than previous model years. 87-92Camaro and +Pontiac systems use a small diameter distributor with an external coil. 87-91 Corvettes’ still use the HEI distributor. Either distributor will work, however the connectors are different. FIS can furnish adaptors -connectors for either application. The HEI Distributor for the 85-86 5.0L engine has the number 1103679 stamped in the aluminum casting at the base of the distributor. The 85-91 5.7L HEI unit is stamped 1103680. The smaller diameter (72mm) distributor is stamped 1103479 on the metal plate beneath the distributor. The72mm Distributor was furnished with 5.0L/5.7L engines on the Camaro, and Pontiac engines 87-92.

As mentioned earlier the LT1/LT4 has an optical sensor and is significantly different than the HEI system. Distributors are not interchangeable for these different engines.

Fuel Pumps

The OEM fuel pump for TPI/LT1 is an "in tank" fuel pump with an operating rating of 50 PSI and 24 GPH. This pump is recommended for all vehicles with in-tank pump mountings. We also offer a chassis mounted fuel pump which has an operating rating of 60 PSI and 30 GPH. This pump is also an AC DELCO unit. It is important to note that Throttle Body Injection systems operate at 12 PSI. Almost all carbureted systems operate at low pressure utilizing a mechanical pump. An electric pump is definitely required as referenced above for all Port Injection systems. A return line is required to the fuel tank. A 3/8 or 5/16inch supply line is required. 3/8 is recommended. 5/16 inch is recommended for the return line. The fuel tank must be vented so as not to buildup pressure. Recommended location for the fuel pump is close to the fuel tank.

Fuel Injectors

There are a number of Fuel Injectors on the market today the following injectors have been furnished on GM OEM systems: Lucas, Bosch, Rochestor and Multec. The prices vary considerably and performance differences are hard to detect. Basically they are sized for application. The 5.0L injector is sized to deliver approximately 4.05 milligrams of fuel with a 2.5 millisecond pulse or 18.13 lbs per hr at approximately 36 PSI. The 57L injector is sized to deliver approximately 4.83 milligrams of fuel with a 2.5 millisecond pulse or 23.92 lbs per hr at approximately 43.5 PSI. This information is typical for all manufacturers and flow rates will vary slightly even between identical injectors.


Lucas is presently pushing their new High Output Disc Injector and is referred to as a High Performance Injector. This product was introduced in March of 9l. They are competitively priced at approx $60.00 each. A wide variety of flow rates are available to include 18lb/hr, 24lb/hr, 28lb/hr, and 37 lb/hr. These are all 16.2 Ohms and will work well with all GM TPI ECM's Rochestor injectors are presently furnished for the 90-94 GM 5.7L engine. It has an all metal nozzle and performs well. Priced at approx $75.00 each. Bosch injectors are also an excellent choice at approx $87.00 each.


While there are significant differences between the TPI and LT1 induction systems and computers, the injectors are essentially the same. Sequential port injectors and batch fired injectors are sized in the same manner. We regret that we have not been able to make DYNO comparisons of these products. We will be glad to share whatever we hear on this subject with you when you call. FIS stocks all of the injectors referenced.

Wiring Harnesses

The 1985 Engine Harness for all vehicles incorporates a MAFS module which plugs into the harness in the vicinity of the ECM. If you are purchasing a system thru a salvage yard, be sure to secure this component which mounts piggy back on the ECM. A single relay and the ESC module are mounted on a common bracket in the engine compartment. The relay is the fuel pump relay.

The 1986-89 Harness has three relays and the ESC module mounted in the engine compartment. The 89 harness does not incorporate connectors for the cold start system. Please note that a mass air flow sensors required on all systems thru l989. Please note that while the connectors for the 85 ECM and the 86-89 ECM are the same, they are NOT interchangeable. The ECM's are different.


The 90-92 systems are considerably different than their predecessors. The 90-92 systems use a Manifold Air Pressure (MAP) sensor in lieu of the Mass Air Flow Sensor. This system is referred to as a Speed Density System. The Electric Spark Control (ESC) module is also incorporated in the ECM. All hardware components remain the same ie., intake runners, fuel rails, throttle body, distributor and intake manifold. The EST module, in the distributor and knock sensors are different than the earlier models and must be matched. All hardware components are interchangeable with

earlier models.


While the 90-92 systems are cheaper to manufacture, it is questionable as to whether Speed density is better than the Mass Air Flow System, especially when GM brought the MAF back in the 94 LT1. But who are we to question GM engineering. All systems appear to perform very well indeed. The 90-94 system has a single relay for the fuel pump mounted in the engine compartment. There is no ESC module as previously discussed. These functions are performed by a module in the ECM/PCM. The ECM's for the 90- 92 Camaro and Pontiac are different than the 90/91 Corvette.


The Pontiac and Camaro use a 1227730 ECM and the Corvette uses a 1227727 ECM. The difference between the two is in the ECM enclosure and ECM connectors. The Corvette enclosure is built for mounting in the engine compartment. Camaro/ Pontiac are built for mounting in the passenger compartment. Internally they are the same. Calibrators are interchangeable. It should also be noted that the Assembly Line Diagnostic Link (ALDL) connector ISNOT normally part of the Factory Engine Harness. It is normally part of the instrument panel harness. The factory engine harness also includes a number of connectors which are not required for "Off Road Use". These connectors are Air Management, Transmission, EGR, Electric Fan, Instrument Panel Oil Pressure Sender, Water Temperature sender, AC High Pressure Switch, VSS and VATS module to mention a few.


From 94 and up it’s the PCM and no calibrators. The PCM for the LT1 is the same in the Corvette, Camaro, Firebird, Buick and Caprice. This unit is Programmable as previously discussed. These units are completely different than their predecessors. FIS can program these units for any LT1/engine transmission combination. Performance and special calibrations are also available.


In 96 OBDII computers were introduced. These computers require a full compliment of emissions equipment, i.e., 4 O2 sensors, EGR control and air pumps on passenger car engines. The LT1 engines 96 and up will work with 94 electronics and can best up for 'Off Road' applications. The Vortec V8' can also be retro-fitted with earlier electronics for "off road" applications. The LS1 however requires a full compliment of emissions equipment. The 98 GM trucks incorporate a "Passlock" system that is similar to the earlier "Passkey" system found in passenger cars (Vehicle Anti Theft System). It is easier to use a 96-97 computer than it is to try and run the 98 computer with a passlock system.


1997 Chevrolet introduced the LS1 in the C5 Corvette. This is an aluminum block engine which produces 345HP and 340 ft/lb torque. These engines do not have distributors. All timing is done via a crank shaft and camshaft position sensor. The reluctor for engine timing is secured, internally, to the crankshaft at the rear of the block. There is a separate ignition coil for each cylinder. 1999 The 4.8L-LR4 / 5.3L-LM7 / 6.0L-LQ4 engines appeared in the GM trucks for the 1st time. These engines are of the same basic design as the LS1; in fact many of the parts are interchangeable. There will be some neat combinations made in the near future by swapping crankshafts etc.

1986 corvette wiring info

http://tpiparts.net/90_92_speed_density_sensors/

http://tpiparts.net/85_89_maf_sensors/