handy fuel system trouble shooting flow chart & info


Staff member
IF youve purchased a vette thats been sitting awhile and it won,t start and run youll need to verify the fuel pump has electricity and its at least running, if it is at that point,drain the fuel tank, replace the fuel filter and fill the tank with fresh high test gas and two cans of fuel injector cleaner and 6 oz of marvel mystery oil, swap in new spark plugs and personally... ID also install a new fuel pump and regulator but that MAY not be necessary
if the car won,t run, youll probabbly need the fuel pump and regulator

If your trying to isolate and test and get the engine tune correct, on any efi system,
Id suggest you leave the fuel pressure alone if its at least 40 psi and does not exceed about 58 psi,
and if the fuel pressures consistent, and set the spark plug gap at .043-.045 max and keep th engine coolant temps as consistent and near about 180F-190F as you can get them,
the fewer variable your forced to deal with the better, make the changes in INJECTOR PULSE DURATION and ignition advance curves
to vary the fuel/air ratios and cylinder pressure
to avoid detonation and tuning issues
always start by verifying what your dealing with in temps fuel pressure and sensor function, pull trouble codes and read and tuning instructions, get a shop manual and verify sensor functions and electrical connections electrical grounds, ignition firing orders, do a compression test and verify the valve lash, set the valves if that's required, and make sure your not dealing with partially clogged catalytic converter carefully, verify what your dealing with, don,t guess, verify.
I can assure you that most problems are related to guessing or defective sensors, or assuming somethings working, that you fail to verify, like the ohms resistance in ignition wire or the firing order or verifying TDC, vs the damper/timing tabs
having a set of multi meter/timing light, compression gauge, vacuum and fuel pressure gauges and a shop manual is critical.


http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf





get a code reader and a multi meter , pull codes check fuses and get a shop manual for your year corvette the auto parts store books leave out a great deal of info

autowiz said:
So on your FP relay pin D is a drk grn/wht wire and it is power to energize the relay from the ecu. This pin should have power for 2 seconds after you turn the key on and when cranking. Pin E is a red wire that connects the relay to the pump. There is a fuse in between the relay and the pump, it is fuse #20 in your passenger compartment fuse block. Pin E is the output of the relay that is controlled by pin D so it, too should have power for 2 sec when the key is turned on and while cranking. Pin A is Power coming into the relay. This is an orange wire and it goes to the stack of fuse links behind your battery. You should have power at the orange wire pin A all the time. If you do not have power at this orange wire then you might need to replace one of the fuse links behind the battery. And finally pin F is a blk/wht wire and should be connected directly to chassis ground.

Wait, did I say finally?? Well there is one more pin. The cool pin of the fuel pump relay. Pin C. And why is pin C the cool pin? Well because pin C is a red wire that connects directly to the ALDL connector under the dash for easy diagnostics. It goes to pin G of the ALDL connector. It is a red wire on this end also. This wire connects ultimately directly to the fuel pump. So whenever the pump has power, this pin has power. This pin at the ALDL is a great place to begin the diagnostic process for your trouble code.
if your tracing a fuel pressure related problem these links above will usually help

once youve drained the gas and removed and cleaned or replaced the fuel pump youll see you can easily clean the tank interior with paper towels or shop rags if its not too bad, thru the pump access port


its not necessary to drain the tank but its a good idea to do so,
step one have the parts on hand PLUS 3 ft of 3/8" fuel line and 1 ft of 5/16" fuel line , I know, you may not need the fuel line but in many cases its faster and easier to remove the old line and replace with new ones
hose clamps, youll want several 1/2" size for the lines


heres related info that may be useful
VetNutJim said:
Good check with the NOID light.............bobbyrxxxx.....

Question: Did this symptom start after any work was done to the engine?

Hmmm.... That would lead me to think there is a problem in the distributor.
There is a pickup coil and a reluctor ring IIRC that sends tach pulses to the ECM. When the ECM receives the pulses it activates the Injector Drive circuitry which then pulses the injector low side to ground thru the electronic injector driver circuit.

But before we go that far, can you check to make sure one side of the injectors are getting +12 Volts?
It's ALWAYS a good idea to eliminate the MOST SIMPLE cause of a problem before going to the more complex ones.

A little 'Troubleshooting 101' there, LOL.

Use any old multimeter, set to 20 volt scale or whatever scale you have above 12 volts. If it's an auto range meter just set it to chsck DC voltage.

Pull any one of the injector plugs.
Pick one up front that's easy to get to.

You will see TWO little metal contact or connectors in the injector harness plug connector.
Turn the ignition key to the 'on' position.
Place the negative meter lead to ground. (engine metallic surface)
Place the red or positive lead on one of the two injector plug metal connector surfaces.
See if you have +12 volts there. If not, move the meter lead to the other injector plug connector surface.
See if you have +12 volts there.
Turn the ignition key off.

The injectors are wired in PARALLEL for each BANK. This is a 'batch fire' system for the injectors. Fuel is 'made available' but there is no individual injector pulse for each cylinder as in the Sequential Fuel Injection systems.

They ALL turn on at the same time but are split up into TWO sides like a stereo.
The ECM 'fires' one bank then the other.
+12 VOlts is supplied to ALL the injector 'positive' terminals whenever the key is on.

So make sure you have +12 volts at the injector plug.
You really only need to check ONE injector plug on each side of the engine to determine this..... because they are wired in parallel.

If you have the +12 volts there then the distributor ignition module may be bad or the distributor may have 'pickup' circuit trouble.

TIP: Check the connectors on the side of the distributor to make sure they are plugged in well to the distributor.

Check the large flat connector coming from the distributor to make sure it is plugged in good.
You guys don't laugh, I've left them unplugged a few time myself.

TIP: If the +12 Volt lead going into the distributor is not connected or not making a good connection, the engine will not start AND IIRC the tach pulses will not be fed back to the ECM so.... the injectors will not pulse.

Don't rule out ANYTHING, no matter how simple, as being a LIKELY SUSPECT.
More Troubleshooting 101, LOL.

The 'reluctor ring' is a round device inside the distributor housing with 8 'tips' on it sort of like an 8 sided star. As the tips pass by the pickup coil, a 'reference pulse' is generated that is wired back to the ECM.

THis let's the ECM detect the engine is turning and supplies reference for the ignition module.
Until the engine is turning, the injectors will not fire as ther is no reason for them to OTHER than the ECM does 'prime' the engine during the before start sequence.

That's why these things normally fire up soon as you engage the starter.
The ECM has done all the 'work' to set the correct start conditions before the starter has a chance to turn the engine over more than a couple of rounds.

My 91 fires up in about 1/2 second even if it's been setting for weeks.

BTW, this doesn't sound like a 'too difficult' problem so hang in there, you will find it.

Post back here with you reserach and I or someone else here will give you more tips on finding the problem.

fuel pump

fuel pump screen

fuel filter
(optional but a GREAT IDEA)


ok, step one,
make darn sure the keys are out of the car and the battery is disconnected for extra safety

step two, open the fuel fill door center rear deck where you normally fill the car and remove the gas cap

step three
remove the four very small torx screws in the corners and lift off the door assembly

step four
theres a rubber bib fuel spill tray)(around the fill spout, remove the gas cap and work the bib fuel spill tray ) (out , and disconnect the water drain line and label it with masking tape/pen

step five
label the three lines with masking tape/pen (upper line/lower line /left side line)
remove each at the central point in the opening, then disconnect the electrical connector on the lower edge of the opening

step six
remove the 8 10mm bolts and look carefully at where the components go, after they are removed the pump lifts up and out, the pump normally comes with instructions also, but its fairly simple, the pump, lines and fuel level sensor lifts out as a sub assembly, look thru the link below for pictures and more info

the search feature, is always an option here, on this site, but to save time , look at the sub links in these threads, to find sources for replacement electrical connectors, and NAPA can frequently ORDER replacement connectors for repairs at about 3- 5 times the cost youll find them at else ware, but at times getting the part the next day beats waiting a week so the price may be justified. if its a connector thats likely to break frequently buy extras, and have them handy





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Staff member
info that might help (before you ask, yeah the LT1 is very similar)

L-98 Engine Start Sequence

knowing whats going on and WHY can help

http://members.shaw.ca/corvette86/Component Location View 86.pdf













When you start an L-98 engine Corvette, a series of events take place that causes the engine to run. Knowing the sequence will help you troubleshoot no start conditions.

Fuel Rail Pressurization:

When you first turn the key to the “on†position, the fuel pump will run for 2 seconds pressurizing the fuel rails. There is a Shraeder valve on the passenger side fuel rail near the rear of the engine and if you measure the pressure there after the pump runs, you should see between 40-42 pounds of pressure. The reading will go to 38-40 pounds nominal once the engine is running.test by attaching a fuel pressure gauge to the fuel rail at the shrader valve, on TPI and LT1 engines its located on the pass side fuel rail

Initial Crank Action:

If you then rotate the key to the start position (assuming the anti-theft system has not disabled the starter), the engine will rotate.

Once the oil pressure has reached 4 PSI, the oil pressure switch will close allowing the fuel pump to run. (Note that you should have a black oil pressure switch/sender. It is mounted behind the distributor on the driver’s side and if it is not black, it is suspect due to a run of bad units that stayed in the GM parts pipeline for some time).

The distributor will send a string of pulses to the ECM (Engine Control Module) in response to the engine being rotated by the starter. These pulses continue as long as the engine turns (both starting and running) and if they are not present, the engine will not run.

ECM Reaction:

If the ECM sees oil pressure greater than 4 PSI and the reference pulses from the distributor, it will energize the injector drivers which will begin pulsing the injectors on for 4 ms (milliseconds) periods. (In the L98, all injectors on one side of the engine fire at the same time followed by all injectors on the other side firing at the same time. On the LT-1, the injectors are fired individually at the appropriate time).

The ECM will also pull in the fuel pump relay in effect paralleling it electrically with the oil pressure switch. (If the fuel pump relay fails, you can still normally get the car to start and run unless you can’t make at least 4 PSI oil pressure. This is a “limp home mode†feature put in place to allow for a fuel pump relay failure).

The ECM also monitors the TPS (Throttle Position Sensor mounted on the throttle body assembly) and wants to see .54 volts at this time. If it sees appreciably more than 0.54 volts, it will assume the engine is flooded and the driver has pressed the accelerator to the floor to clear the flooded condition and restrict the fuel flow as a result. (.54 volts during start and at idle from the TPS is very important to both starting and run performance.)

Assuming the ignition module is good (meaning there is a spark of sufficient intensity to ignite the fuel), the engine will “catchâ€.

Engine "Catches":

When the engine catches, the MAF (Mass Air Flow sensor mounted just ahead of the throttle body) sends a signal to the ECM advising that air is flowing and also just how much air is being pulled through to the intake manifold. The ECM takes note of the amount of air being consumed and adjusts the injector pulse width to around 2.2 ms nominally so as to attain a proper air/fuel mixture to insure combustion. (This is how the 1985 through 1989 L-98 works. For information on the 1990 and 1991 L-98 variant, see the Note below).

The engine should show an initial idle speed of around 900-1100 RPM and then slowly diminish to 600-700 RPM unless the air conditioner is on in which case it will run at around 800 RPM.

If this does not happen, the Idle Air Mixture valve (located on the throttle body) may be misadjusted. Alternatively, there may be a leak in the intake manifold or another vacuum leak may be present. Listen for hissing sounds---there should be none.

ECM Mode:

The engine will now be in Open Loop mode meaning that the ECM is controlling the air/fuel mixture by referencing values stored in memory.

Once the Oxygen sensor (mounted on the exhaust pipe) reaches operating temperature of several hundred degrees, the Manifold Air Temperature (MAT) sensor shows an intake air temperature of more than 140 degrees and the Engine Coolant Temperature (ECT) has reached 160 degrees, the computer will switch to closed loop mode meaning the Oxygen sensor’s output is examined along with the MAT and ECT outputs and the ECM adjusts the injector pulse widths (more “on time†or less “on timeâ€) to constantly strive for a 14.7:1 air/fuel mixture which is the best mixture to hold down pollution.

Note that prolonged idling can force the computer back into open loop mode.

Note: In 1990, the MAF was eliminated from the engine in favor of a speed/density system. This system uses a sensor called the MAP sensor which measures the Manifold Absolute Pressure (hence the name MAP) and compares it with the atmospheric pressure outside the intake manifold. This information, coupled with the Manifold Air Temperature, Engine Coolant Temperature and Engine RPM is used by the ECM to determine the amount of air entering the cylinders. It is a different way of reaching the desired 14.7:1 air-fuel mixture ratio but functionally is like the MAF system in that the ECM uses the feedback to control the "on time" for the injectors.

Corvette used this approach in the 1990 and 1991 L-98 engines and in the 1992 and 1993 LT-1 engines. With the 1994 model C4, they went back to the MAF system. Note that MAF based systems are far more accurate since they measure air flow directly whereas the MAP system infers air flow indirectly. A multitude of things can throw the calculation off and Corvette returned to the MAF system beginning with the 1994 C4 (with a MAP backup). From a troubleshooting standpoint, the MAP operation comes into the sequence the same place that the MAF does.


If you have a no start condition or if the L-98 starts and then dies, check the above items in sequence to see if all the events are occurring as required.

A Scan Tool makes this job much easier and is a highly recommended troubleshooting aid for these sorts of problems.


Most of the C4 Corvettes used a MAF (Mass Air Flow) sensor to determine how much air is being pulled into the intake manifold. The exceptions are the 1984 Corvette that used a speed density system--a sort of predictive method of measurement---and the 1990 through 1993 C4 models which were also speed density based. In 1994, Corvette went back to the MAF based system but used the speed density approach as a back up. (1989 Bosch MAF installation shown at right).

A Mass Air Flow sensor has an extremely fine wire inside its bore. The 1985 through 1989 C4 engines used a Bosch MAF sensor that heated the wire to 100 C. The 1994 and later C4 models used a AC/Delco MAF that heated the wire to 200 C. The amount of current required to reach the temperature is measured in each case. (Note: the LT-5 engine used in the ZR-1 used a speed density system and continued to use that system in 1994 and 1995 since the engines had already been made prior to the last two years of production. The ZR-1 therefore has no MAF even after Corvette went back to the MAF based system).

Theory of Operation

As the air travels past the heated wire enroute to the intake manifold, it will cool the wire and additional current is added to again heat the wire to the design temperature. Since the amount of air moving past the sensor is directly related to the amount of cooling experienced by the heated wire, a feedback condition is established whereby the exact amount of moving air is directly related to the amount of current passing through the wire and the intake air is therefore precisely measured.

Once the amount of air is known, the computer controlling the engine can add or subtract fuel as required to maintain the magic 14.7:1 air-fuel mixture resulting in the cleanest burn possible from an emissions (pollution) standpoint.

It does this by varying the "on time" of the fuel injectors. The injectors are pulsed on and off and the width of the pulse is lengthened or shortened as required. When you first start a typical engine, the pulse width is around 4 milliseconds but as soon as the engine "catches" the pulse width is shortened to about 2.2 milliseconds for idle. During operation, the measured air flow through the MAF will cause the computer to increase or decrease the pulse width as explained above.

MAF Operating Conditions

The Bosch MAF is more complex than the AC/Delco version. Both measure the air flow but the Bosch MAF has a circuit called the 'burn-off circuit' that cycles on for about 2 seconds when you shut the engine down. This circuit heats the wire to a high enough temperature to burn off any residue that may have collected on the wire during operation. If you are in a quiet area, you can hear the relays click on and then off on a 1985-1989 C4 as the burn-off cycle occurs.

There are two relays involved with the Bosch MAF: A power relay that passes current to the MAF wire during normal operation and the burn-off relay that provides the current for the cleaning cycle. Both are located on the firewall in the engine compartment, just behind the battery on the drivers side. Bad MAF power and burn-off relays can cause hard starting problems and should be changed periodically as preventative measure and any time you experience hard starting conditions.

The AC/Delco MAF has a power relay but no burn-off relay. For this reason, you should pay even closer attention to the condition of your air filter on a later model C4 than normal since a contaminated wire in a AC/Delco MAF is going to stay contaminated for the most part and cause false signals to be passed to the computer.

Also, the Bosch MAF outputs its information as a analog signal to the computer but the AC/Delco sends its signal as a digital component of varying frequency. For this reason, you cannot measure it's operation directly.

A scan tool is generally the best way to troubleshoot engine problems and with the 1994 and later Corvette, it is virtually mandatory. (An oscilloscope will also work on the AC/Delco MAF but a regular test meter will not).

MAF Problems

Faulty MAF sensors will normally light the check engine light on the drivers information center if the problem is constant and store a trouble code. If intermittent, a trouble code will still be stored as long as the battery is not disconnected.

Normally, the problem is a poor connection at the sensor and wiggling the wires, unplugging and reinserting the connector will often cure the problem.

A faulty MAF will normally cause a no start or difficult start condition and although you can eventually get the car into the "limp-home" mode in most cases, you need to attend to the problem ASAP.

this flow chart might help


AC/Delco sensors can become intermittent or give false readings if the wires become contaminated as explained above.

The MAF is a critical part of the emission control system and as such will cause the computer to react to problems very quickly, setting trouble codes and reducing performance in ways that cannot be ignored for long.

MAF Mods

The Bosch MAF is often modified by removing the two screens that are present in the front and rear of the cylinder. Removing these screens significantly increases the air flow through them and this results in more horsepower. Removing the screens is an old trick from the Corvette Challenge days in 1988 and 1989. It does work but is illegal in many states so be advised not to do anything that will get you arrested for a pollution violation.

The AC/Delco MAF is not readily modified. It is what it is but since it is a larger diameter than the Bosch, it responds well to changing the air filter to a free flowing type such as the K&N filter.
Welcome to C4 vette codes it is very ....repeat very
important that if you are not savvy of working on your
vette ...you would be better off - taking your car to a
dealership for repairs on your trouble codes.
However if you feel that you want to dive right in ..than you
have come to the right place.First locate your car's alcl
this component is located just below the instrument panel and
to the left of the center console. Remove the plastic cover
the first two slots to your right are the A & B slots for a drawing of
the alcl module's picture is added below.
The A slot is the diagnostic slot and the B slot is the ground
slot. insert the computer key into these slots (with the engine
off) this is very important...now only put the ignition key
to on ( not start !!!) the check engine light will display a
code 12 which is one flash followed by two flashes.
this code will be flashed three times ..followed by the
trouble code stored in your car's computer.
what ever the code is it will be flashed three times.
have a paper and pencil ready and write down the
code .

code 13 =1 flash followed by 3 flashes =>oxygen sensor
code 14 =1 flash followed by 4 flashes =>coolant sensor
code 15 =1 flash followed by 5 flashes =>coolant sensor
code 21 = 2 flashes followed by 1 flash =>throttle position sensor
code 22 = 2 flashes followed by 2 flashes=> throttle position sensor
code 23 = 2 flashes followed by 3 flashes=> manifold air temp sensor
code 24 = 2 flashes followed by 4 flashes=> vehicle speed sensor
code 25 = 2 flashes followed by 5 flashes=> manifold air temp sensor
code 32 =>egr system
code 33 =>map sensor
code 34 =>maf sensor
code 35 => idle air control
code 41 => cylinder select error
code 42 => electronic spark control
code 43 => electronic spark control
code 44 => lean exhaust
code 45 => rich exhaust
code 51 => PROM
code 52 => fuel calpak
code 53 => system over voltage
code 54 => fuel pump circuit
code 55 => ecm
code 62 => oil temp
please remember that if you have the computer key installed
in the alcl and you start the engine ( you will ruin the engine's computer
only put the ignition to on (not to start)
If you should get a check engine soon display.. you can use
the above procedure and codes to buy the right part
or at the very least to keep from getting taken for a ride
and be made to pay hight prices for some inexpensive
module that you could have installed yourself.
You never ask a barber if you need a haircut ..
so you have to be on guard they will see you comming
a mile away.
If your engine displays a trouble code ... your engine will
go into limp mode ..it will still run but very poorly.
you might be able to reset the computer if it will not start
( just to get home ) by disconnecting both battery cables
and re-installing them ...this is not recommended ..but if
you are stranded it might help unitl you get your car home
or to a repair shop..good luck

1985 TO 1991:

Code #12: Normal No Codes.
Code #13: Open Oxygen Sensor Circuit.
Code #14: Coolant Sensor Circuit Low.
Code #15: Coolant Sensor Circuit High.
Code #21: Throttle Position Sensor High.
Code #22: Throttle Position Sensor Low.
Code #23: Manifold Air Temperature Circuit High.
Code #24: Vehicle Speed Sensor.
Code #25: Manifold Air Temperature Circuit Low.
Code #32: EGR System Failure.
Code #33: Mass Air Flow Sensor High.
Code #34: Mass Air Flow Sensor Low.
Code #36: Mas Air Flow Sensor Burn-Off Function Fault.
Code #41: Cylinder Select Error.
Code #42: Electronic Spark Timing.
Code #43: Electronic Spark Control.
Code #44: Lean Exhaust indication.
Code #45: Rich Exhaust Indication.
Code #46: Vehicle Anti Theft Fault.
Code #51: Faulty Mem-Cal.
Code #52: Fuel Calpak Missing.
Code #52(1990-91 Corvette Only): Engine Oil Temperature Sensor Low.
Code #53: System Over Voltage.
Code #54: Fuel Pump Circuit Low Voltage.
Code #55: Defective ECM.
Code #62: Engine Oil Temperature Sensor Circuit High.

ECM CODES 1992 TO 1993:

Code #12: Normal No Codes.
Code #13: Left Oxygen Sensor Circuit.
Code #14: Coolant Temperature Sensor Circuit High.
Code #15: Coolant Temperature Sensor Circuit Low.
Code #16: Opti-Spark Ignition Timing System.( Low Pulse)
Code #21: Throttle Position Sensor Circuit High.
Code #22: Throttle Position Sensor Circuit Low.
Code #23: Intake Air Temperature Sensor Circuit Low.
Code #24: Vehicle Speed Sensor Circuit.
Code #25: Intake Temperature Sensor Circuit High.
Code #26: Quad-Driver Module #1 Circuit.
Code #27: Quad-Driver Module #2 Circuit.
Code #28: Quad-Driver Module #3 Circuit.
Code #32: Exhaust Gas Recirclation Circuit.
Code #33: Manifold Absolute Pressure Sensor Circuit Low.
Code #34: Manifold Absolute Pressure Sensor Circuit High.
Code #36: Opti-Spark Ignition Timing System. (High Resolution Pulse.)
Code #41: Electronic Spark Timing Circuit Open.
Code #42: Electronic Spark Timing Circuit Grounded.
Code# 43: Electronic Spark Control Circuit.
Code #44: Left Oxygen Sensor Circuit Lean.
Code #45: Left Oxygen Sensor Circuit Rich.
Code #51: Mem-Cal Error.
Code #52: Engine Oil Temperature Sensor Circuit Low.
Code #53: System Voltage.
Code #55: Fuel Lean Monitor.
Code #56: Vacuum Sensor Circuit.
Code #61: Secondary Port Throttle Valve System.
Code #62: Engine Oil Temperature Sensor Circuit High.
Code #63: Right Oxygen Sensor Circuit Open.
Code #64: Right Oxygen Sensor Circuit Lean.
Code #65: Right Oxygen Sensor Circuit Rich.
Code #66: A/C Pressure Sensor Circuit Open.
Code #67: A/C Pressure Sensor Circuit. (Sensor or A/C Clutch Circuit Problem)
Code #68: A/C Relay Circuit Shorted.
Code #69: A/C Clutch Circuit.
Code #72: Gear Selector Switch Circuit.

CODES 1994 TO 1996:

DTC #11: Malfunction Indicator Lamp Circuit.
DTC #13: Bank #1 Heated Oxygen Sensor #1 Circuit:
DTC #14: Engine Coolant Temperature Sensor Circuit Voltage Low.
DTC #15: Engine Coolant Temperature Sensor Circuit Voltage High.
DTC #16: Distributor Ignition System Low Pulse.
DTC #18: Injector Circuit.
DTC #21: Throttle Position Sensor Circuit Voltage High.
DTC #22: Throttle Position Sensor Circuit Voltage Low.
DTC #23: Intake Temperature Sensor Circuit Voltage High.
DTC #24: Vehicle Speed Sensor Circuit.
DTC #25: Intake Air Temperature Sensor Circuit Voltage Low.
DTC #26: Evaporative Emission Canister Purge Solenoid Valve Circuit.
DTC #27: EGR Vacuum Control Signal Solenoid Valve Circuit.
DTC #28: Transmission Range Pressure Switch Assembly Fault.
DTC #29: Secondary Air Injection Pump Circuit.
DTC #32: Exhaust Gas Recalculation.
DTC #33: Manifold Absolute Pressure Sensor Circuit High.
DTC #34: Manifold Absolute Pressure Sensor Circuit Low.
DTC #36: Distributor Ignition System High Pulse.
DTC #37: Brake Switch Stuck On.
DTC #38: Brake Switch Stuck Off.
DTC #41: Ignition Control Circuit Open.
DTC #42: Ignition Control Circuit Shorted.
DTC #43: Knock Sensor Circuit.
DTC #44: Bank 1 LF Heated Oxygen Sensor #1 Circuit Lean.
DTC #45: Bank 1 LF Heated Oxygen Sensor #1 Circuit Rich.
DTC #47: Knock Sensor Circuit Or Module Missing.
DTC #48: Mass Air Flow Sensor Circuit.
DTC #50: System Voltage Low.
DTC #51: EEPROM Programming Error.
DTC #52: Engine Oil Temperature Sensor Circuit Voltage Low.
DTC #53: System Voltage Low.
DTC #55: Fuel Lean Monitor.
DTC #58: Transmission Fluid Temperature Sensor Circuit Low.
DTC #59: Transmission Fluid Temperature Sensor Circuit High.
DTC #62: Engine Oil Temperature Sensor Circuit Voltage Low.
DTC #63: Bank 2 RF Heated Oxygen Sensor #1 Circuit Open.
DTC #64: Bank 2 RF Heated Oxygen Sensor #1 Circuit Lean.
DTC #65: Bank 2 RF Heated Oxygen Sensor #1 Circuit Rich.
DTC #66: A/C Refrigerant Pressure Sensor Circuit Open.
DTC #67: A/C Pressure Sensor Circuit Sensor or A/C Clutch.
DTC #68: A/C Relay Circuit.
DTC #69: A /C Clutch Circuit.
DTC #70: A/C Clutch Relay Driver Circuit.
DTC #72: Vehicle Speed Sensor Loss.
DTC #73: Pressure Control Solenoid Circuit Current Error.
DTC #74: Traction Control System Circuit Low.
DTC #75: Transmission System Voltage Low
DTC #77: Primary Cooling Fan Relay Control Circuit.
DTC #78: Secondary Cooling Fan Relay Control Circuit.
DTC #79: Transmission Fluid Overtemp.
DTC #80: Transmission Component Slipping.
DTC #81: Transmission 2-3 Shift Solenoid Circuit.
DTC #82: Transmission 1-2 Shift Solenoid Circuit.
DTC #83: Torque Converter Solenoid Voltage High.
DTC #84: 3-2 Control Solenoid Circuit.(Auto Only).
DTC #84: 2nd And 3rd Gear Blockout Relay Control Circuit.
DTC #85: Transmission TCC Stock On.
DTC #90: Transmission TCC Solenoid Circuit.
DTC #91: One To Four Upshift Lamp(Manual Only).
DTC #97: VSS Output Circuit.
DTC #98: Tachometer Output Signal Voltage Wrong.
_________________you really can,t be effectively at playing mr-fix-it with out the correct tools

See the DTC page for P0.. (generic) codes and Glossary for terms and acronyms..

P1031 H02 Sensor Heater Control Circuit Problem
P1106 intermittent high or low Voltage in circuit of sensor MAP
P1107 MAP Sensor Circuit Intermittent Voltage Low
P1108 BARO to MAP Signal Circuit Comparison Too High
P1111 IAT Sensor Circuit Intermittent Voltage High
P1112 IAT Sensor Circuit Intermittent Voltage Low (except Catera)
P1112 Intake Plenum Switchover Valve Control (Catera)
P1113 Intake Resonance Switchover Valve Control
P1114 ECT Sensor Circuit Intermittent Voltage Low
P1115 ECT Sensor Circuit Intermittent Voltage High
P1120 Throttle Positioning Sensor 1 Circuit
P1121 Throttle Positioning Sensor 1,2 Circuit Performance/ Fuel Injector Secondary System Circuit Low
P1122 TPS Circuit Intermittent Voltage Low
P1125 APP System
P1133 HO2S/O2S Insufficient Switching Sensor 1 Or Bank 1 Sensor1
P1134 HO2S Transition Time Ratio Bank 1 Sensor 1
P1137 HO2 Sensor Low Voltage During Power Enrichment
P1138 HO2 Sensor High Voltage During Decel Fuel Cutoff
P1139 HO2S Insufficient Switching Bank 1 Sensor 2
P1140 HO2S Transition Time Ratio Bank 1 Sensor 2
P1141 HO2 Sensor Heater Control Circuit (Bank 1 Sensor 2)
P1153 HO2S Insufficient Switching Bank 2 Sensor 1
P1154 HO2S Transition Time Ratio Bank 2 Sensor 1
P1158 HO2 Sensor Shift Rich (Bank 2 Sensor 2)/ Engine Metal Over-Temperature Protection
P1161 HO2 Sensor Heater Control Circuit (Bank 2 Sensor 2)
P1171 Fuel System Lean During Acceleration
P1187 Engine Oil Temperature Sensor Circuit Voltage Low (except 1997 Corvette)
P1187 Engine Oil Pressure Sensor Circuit Voltage Low (1997 Corvette)
P1188 Engine Oil Temperature Sensor Circuit Voltage High (except 1997 Corvette)
P1188 Engine Oil Pressure Sensor Circuit Voltage High (1997 Corvette)
P1189 Engine Oil Pressure Switch Circuit
P1200 Injector Control Circuit
P1214 Injection Pump Timing Offset
P1215 Generator Driver Circuit
P1216 Fuel Solenoid Response Time Too Short
P1217 Fuel Solenoid Response Time Too Long
P1218 Injection Pump Calibration Circuit
P1220 Throttle Position (TP) Sensor 2 Circuit Fault
P1221 TP Sensor 1, 2 Performance
P1222 Injector Control Circuit Intermittent
P1250 Early Fuel Evaporative (EFE) Heater Circuit
P1257 Boost Control Condition/Supercharge System Overboost
P1260 Fuel Pump Speed Relay Control Circuit
P1271 Accelerator Pedal Position Sensor 1-2 Correlation
P1272 Accelerator Pedal Position Sensor 2-3 Correlation
P1273 Accelerator Pedal Position Sensor 1-3 Correlation
P1275 Boost Control Condition (except 1997-98 Corvette)
P1275 Accelerator Pedal Positioning (APP) Sensor 1 Circuit (1997-98 Corvette)
P1276 Accelerator Pedal Positioning (APP) Sensor 1 Circuit Performance
P1280 Accelerator Pedal Positioning (APP) Sensor 2 Circuit
P1281 Accelerator Pedal Positioning (APP) Sensor 2 Circuit Performance
P1285 Accelerator Pedal Positioning (APP) Sensor 2 Circuit
P1286 Accelerator Pedal Positioning (APP) Sensor 2 Circuit Performance
P1300 Ignition Coil 1 Primary Feedback Circuit
P1305 Ignition Coil 2 Primary Feedback Circuit
P1310 Ignition Coil 3 Primary Feedback Circuit
P1315 Ignition Coil 4 Primary Feedback Circuit
P1320 ICM 4X Reference Circuit Too Many Pulses (except 1996-98 4.0L)
P1320 ICM 4X Reference Circuit Intermittent No Pulses (1996-98 4.0L)
P1323 ICM 24X Reference Circuit Low Frequency
P1335 Crankshaft Positioning Sensing Circuit
P1336 CKP System Variation Not Learned
P1345 Camshaft To Crankshaft Position Correlation Fault
P1346 CKP Sensor System Variation Not Learned/ Intake Camshaft Position Performance
P1349 Intake Camshaft Position System
P1350 Ignition Control System
P1351 Ignition Control Circuit Voltage High (except 1998 3.1L)
P1351 Ignition Control Circuit Open (1998 3.1L)
P1352 Bypass Circuit Open Or Voltage High
P1359 Ignition Coil Group 1 Control Circuit
P1360 Ignition Coil group 2 Control Circuit
P1361 IC Circuit Not Toggling
P1361 Ignition Control Circuit Voltage Low (Distributor Ignition)
P1362 Bypass Circuit Shorted Or Voltage Low
P1370 ICM 4X Reference Too Many Pulses
P1371 ICM 4X Reference Too Few Pulses (except Caprice, Fleetwood, Impala SS & Roadmaster)
P1371 Distributor Ignition Low Resolution Circuit (Caprice, Fleetwood, Impala SS & Roadmaster)
P1372 CKP Sensor A-B Correlation
P1374 3X Reference Circuit
P1375 ICM 24X Reference Voltage Too High
P1376 Ignition Ground Circuit
P1377 ICM Cam Pulse To 4X Reference Pulse Comparison
P1380 ABS/EBCM/EB(T)CM DTC Detected/Rough Road Data Unusable
P1381 Misfire Detected No EBCM/EB(T)CM/PCM Serial Data
P1401 Exhaust Gas Recirculation (EGR) flow test fault
P1403 EGR Error
P1404 EGR Valve Closed Pintle Position
P1404 EGR Valve Stuck Open Or Circuit Performance
P1405 EGR Error
P1406 EGR Valve Pintle Position Circuit
P1408 MAP Sensor Circuit
P1410 Fuel Tank Pressure System
P1415 AIR System Bank 1
P1416 AIR System Bank 2
P1431 Fuel Level Sensor 2 Circuit Performance
P1432 Fuel Level Sensor 2 Circuit Voltage Low
P1433 Fuel Level Sensor 2 Circuit Voltage High
P1441 EVAP System Flow During Non-Purge
P1442 EVAP Vacuum Switch Circuit
P1450 BARO Sensor Circuit
P1451 BARO Sensor Circuit
P1460 Cooling Fan Circuit (except Catera)
P1460 Misfire Detected With Low Fuel (Catera)
P1483 Engine Cooling System Performance
P1500 Starter Signal Circuit
P1501 Theft Deterrent System
P1502 Theft Deterrent System No Password Received
P1503 Theft Deterrent System Password Improper
P1508 Idle Air Control (IAC) System Low RPM
P1509 IAC System High RPM
P1510 Back-Up Power Supply
P1511 Throttle Control System- Backup System Performance
P1514 TAC System MAF Performance
P1515 Command vs Actual Throttle Position Performance (PCM)
P1516 Command vs Actual Throttle Position Performance (TAC Module)
P1517 TAC Module Processor
P1518 PCM To TAC Module Serial Data Circuit
P1519 Throttle Actuator Control Module
P1520 Park/Neutral Position Switch Circuit, Gear Indicator System
P1523 Throttle Closed Position Performance
P1524 TPS Learned Closed Throttle Angle Degrees Out Of Range
P1526 TPS Learn Not Completed
P1527 Trans Range/Pressure Switch Comparison
P1530 Ignition Timing Adjustment Switch Circuit
P1530 A/C Refrigerant Pressure Sensor Error
P1531 Low Air Conditioning Refrigerant Charge
P1532 A/C Evaporator Temperature Circuit Voltage Low
P1533 A/C Low Side Temperature Sensor Circuit
P1535 A/C/ High Side Temperature Sensor Circuit
P1536 A/C System ECT Overtemperature
P1537 A/C Request Circuit Voltage Low
P1538 A/C Request Circuit Voltage High
P1539 A/C High Pressure Switch Circuit Voltage High
P1540 A/C System High Pressure
P1542 A/C System High Pressure/High Temperature
P1543 A/C System Performance
P1545 A/C Clutch Relay Control Circuit
P1546 A/C Clutch Relay Control Circuit Voltage Low (except 1996-98 Camaro/Firebird & 1997-98 Corvette)
P1546 A/C Clutch Status Circuit Voltage Low (1996-98 Camaro/ Firebird & 1997-98 Corvette)
P1550 Stepper Motor Speed Control
P1554 Speed Control Status Circuit
P1555 Electronic Variable Orifice Fault (Saturn)
P1558 Speed Control (SPS Low)
P1560 Speed Control System/Transaxle Not In Drive
P1561 Speed Control Vent Solenoid
P1562 Speed Control Vacuum Solenoid
P1564 Speed Control System/Vehicle Acceleration Too High (except Catera)
P1564 ECM Battery Voltage Loss (Catera)
P1565 Speed Control Servo Position Sensor
P1566 Speed Control System/Engine RPM Too High
P1567 Speed Control Switches/ABCS Active
P1568 Speed Control (SPS High)
P1570 Speed Control System/Traction Control Active
P1571 TCS Desired Torque Circuit (except 4.0L, 4.6L & 1997-98 5.7L Corvette)
P1571 Traction Control System PWM Circuit No Frequency (4.0L & 4.6L)
P1571 ASR Desired Torque (1997-98 5.7L Corvette)
P1572 Traction Control System Active Circuit Voltage Low Too Long
P1572 ASR/TCS Active Circuit Low Voltage Too Long
P1573 PCM/EBTCM Serial Data Circuit
P1573 Engine Hot Lamp Control Circuit
P1574 EBTCM System/Stop Lamp Circuit Voltage High (except 1997-98 Corvette)
P1574 Stop Lamp Control Circuit (1997-98 Corvette)
P1575 Extended Travel Brake Switch Circuit Voltage High
P1576 Brake Booster Vacuum Sensor Circuit Voltage High
P1577 Brake Booster Vacuum Sensor Circuit Voltage Low
P1578 Brake Booster Vacuum Sensor Circuit Low Vacuum
P1579 Park/Neutral To Drive/Reverse At High Throttle Angle
P1580 Cruise Control Module Move Circuit, Low Voltage
P1581 Cruise Control Module Move Circuit, High Voltage
P1582 Cruise Control Module Direction Circuit, Low Voltage
P1583 Cruise Control Module Direction Circuit, High Voltage
P1584 Cruise Control Disabled
P1585 Cruise Control Inhibit Output Circuit
P1586 Cruise Control Brake Switch 2 Circuit
P1599 Engine Stall Or Near Stall Detected
P1600 PCM Battery
P1600 Serial Communication Between PCM & TCM
P1601 Loss of Serial Communication (Except Catera)
P1601 ECM Overtemperature
P1602 Loss Of EBC/EBTCM Serial Data (Except Catera)
P1602 KS Module Circuit (Catera)
P1603 Loss Of SDM Serial Data
P1604 Loss of IPC Serial Data
P1605 Loss of HVAC Serial Data
P1607 Engine Oil Level Switch Circuit
P1610 Loss Of PZM Serial Data (1996-97 Except 1997 Cutlass & Malibu)
P1610 Failure With Body Function Controller (1997 Cutlass & Malibu)
P1610 Standard Body Module Series Data CKT (1998)
P1611 Loss Of CVRTD Serial Data
P1617 Engine Oil Level Switch Circuit
P1619 Engine Oil Lite Monitor Reset Circuit
P1620 Low Engine Coolant Level (Saturn)
P1621 PCM Memory Performance (Except 1998 5.7L)
P1621 VCM EEPROM Performance (1998 5.7L)
P1623 PCM Prom Error/ Transaxle Temperature Pull-Up Resistor Fault (Saturn Z body)
P1624 Customer Snapshot Data Available (Saturn)
P1625 TCM Flash Checksum Fault (Saturn)
P1626 Theft Deterrent System Fuel Enable Circuit
P1627 A/D Performance
P1628 PCM Engine Control Temp Pull-Up Resistor
P1629 Theft Deterrent System Fuel Enable Circuit Improper Signal Detected During Engine Cranking
P1629 Theft Deterrent Crank Signal Malfunction (1997-98 2.2L, 2.4L, 3.1L & 3.8L)
P1630 Theft Deterrent System/PCM/VCM in Learn Mode
P1631 Theft Deterrent System Password Improper
P1632 Theft Deterrent System Fuel Disabled
P1633 Ignition Supplemental Power Circuit Voltage Low
P1634 Ignition 1 Power Circuit Voltage Low
P1635 5 Volt Reference (A Or 1) Circuit
P1637 Alternator L Terminal Circuit
P1638 Alternator F Terminal Circuit
P1639 5 Volt Reference (B Or 2) Circuit
P1640 Driver 1 Input Voltage High
P1641 MIL Control Circuit (Except 5.7L VINs P & 5 & 1998 3.1L & 3.8L)
P1641 Fan Control Relay 1 Control Circuit (5.7L VINs P & 5)
P1641 A/C Relay Control Circuit (1998 3.1L & 3.8L)
P1642 Vehicle Speed Output Circuit (Except 3.4L, 5.7L VINs P & 5 & 1998 3.8L)
P1642 Fan Control Relay 2 & 3 Control Circuit (5.7L VINs P & 5)
P1642 AIR Control Circuit (3.4L)
P1642 Change Oil Lamp Control Circuit (1998 3.1L Lumina & Monte Carlo)
P1643 Fuel Pump PWM Control Circuit (Except 5.7L VINs P & 5)
P1643 Engine RPM Output Circuit (5.7L VINs P & 5)
P1644 Delivered Torque Output Circuit
P1645 Boost Control Solenoid Circuit (Except 4.0L & 4.6L)
P1645 EVAP Solenoid Output Circuit (4.0L & 4.6L)
P1646 Boost Control Solenoid Control Circuit (Except 4.0L & 4.6L)
P1646 EVAP Vent Valve Output Circuit (4.0L & 4.6L)
P1650 Driver 2 Input Voltage High
P1651 Fan On Relay Control Circuit/Output Driver Module (Quad Driver) 'B' Quickset Fault (Saturn)
P1651 Fan 1 Relay Control Circuit
P1652 Fan 2 Relay Control Circuit (Except Cadillac & Corvette)
P1652 VSS Output Circuit (1996 Corvette)
P1652 Powertrain Induced Chassis Pitch Output Circuit (1997- 98 Corvette)
P1652 Lift/Drive Output Circuit (Cadillac)
P1653 TCS Delivered Torque Control Circuit (Except Caprice, Roadmaster & 1998 3.8L)
P1653 Oil Level Lamp Control Circuit (Caprice, Fleetwood & Roadmaster)
P1653 Fuel Level Output Control Circuit (1998 3.8L)
P1654 A/C Relay Control Circuit (Except 4.0L & 4.6L)
P1654 Cruise Disable Output Circuit (4.0L & 4.6L)
P1655 EVAP Purge Solenoid Control Circuit
P1656 Wastegate Solenoid Control Circuit
P1657 Skip Shift 1-4 Upshift
P1660 Cooling Fan Control Circuits
P1661 MIL Control Circuit
P1662 Speed Control Inhibit Control Circuit
P1663 Alternator Lamp Control Circuit (Except Caprice, Fleetwood & Roadmaster)
P1663 Change Oil Lamp Control Circuit (Caprice, Fleetwood & Roadmaster)
P1664 Skip Shift 1-4 Upshift Lamp Control Circuit
P1665 DBCM/DBTCM Serial Data Circuit (1996-97)
P1665 EVAP Vent Valve Solenoid Control Circuit (1998)
P1667 Reverse Inhibitor Solenoid Control Circuit (1996-97)
P1667 Fuel Pump Speed Control Circuit (1998)
P1670 QDM 4 Circuit
P1671 MIL Control Circuit
P1671 Oil Change Lamp Control Circuit
P1672 Low Engine Oil Level Lamp Circuit
P1673 Engine Hot Lamp Control Circuit
P1674 Tachometer Control Circuit
P1675 EVAP Vent Solenoid Control Circuit
P1676 EVAP Canister Purge Solenoid Control CKT
P1689 TCS Delivered Torque Control Circuit
P1700 MIL Requested By TCM
P1701 MIL Request Circuit
P1740 Torque Management Request Circuits, Transmission & Traction Control (Except Catera)
P1740 Torque Control/Management Request Circuits (Catera)
P1760 Transmission Control Module Supply Voltage Interrupted
P1780 Park Neutral Position Switch Circuit
P1781 Engine Torque Signal Circuit
P1792 ECM To Transmission Control Module Engine Coolant Signal
P1800 ECM To Transmission Control Module Engine Coolant Signal
P1810 ATF Pressure Manual Valve Position Switch Malfunction
P1811 Long Shift & Max Adapt
P1812 TOT Condition
P1814 Torque Converter Overstress
P1819 Internal Mode Switch - No Start
P1820 Internal Mode Switch Circuit 'A' Low
P1822 Internal Mode Switch Circuit 'B' Low
P1823 Internal Mode Switch Circuit 'P' Low
P1825 Internal Mode Switch - Invalid Range
P1826 Internal Mode Switch - Invalid Range
P1835 Kickdown Switch Circuit
P1842 1-2 Shift Solenoid Circuit Low Input
P1843 1-2 Shift Solenoid Circuit High Input
P1845 2-3 Shift Solenoid Circuit Low Input
P1847 2-3 Shift Solenoid Circuit High Input
P1850 Brake Band Apply Solenoid
P1860 TCC PWM Solenoid Circuit
P1864 TCCEnable Solenoid Circuit
P1868 Transmission Fluid Life
P1870 Trans Component Slipping
P1873 Torque CONV Stator Temp Switch Circuit Low
P1874 Torque CONV Stator Temp Switch Circuit High
P1875 4WD Low Switch Circuit Electrical
P1886 Transaxle Shift, Timing Solenoid Performance
P1887 TCCRelease Switch Malfunction
P1890 Throttle Position Signal Input
P1895 Engine Torque Delivered Circuit

especially on the more modern cars that are computer controlled, the days of effectively tuning by ear and vacuum gauge and engine sound went out with carbs
you need a few basic tools, now the list will vary, but you can,t get by by guessing, you neet to know and test now that sensors and CPUs control engine function
heres some basic tools

be sure to get the specific manuals your car and EFI system and ignition system,require FIRST


while it appears to be expensive, it saves you a good deal of money in the long run compared to dealing with the local chevy dealers mechanics, and makes diagnostics far faster, I bought this for the shop and it seems to be a good investment, since between a dealers diagnostics and swapping parts that don,t need changing you could easily spend close to that on just a few problems getting sorted out
youll also want a few basic diagnostic tools





good info

and a book or two




in no time youll be the area wizz kid on chevy injection diagnostics:thumbsup:

This is from http://shbox.com/

A fuel pressure test gauge can be bought at your local auto supply for ~$35. Attach it to the schrader valve that is on the fuel rail. Schrader valve location on 1994-1997

Normal pressure when the engine is not running and lines have been pressurized is 41-47 psi. This same pressure should be observed at wide open throttle (WOT). WOT can be simulated by removing the vacuum hose to the regulator at idle. At idle (because of the effect of the vacuum to the regulator) pressure will be less than what you observe with the vacuum line off. There may be anything from a 3 to 10 psi difference. NOTE: any indication of fuel in the vacuum line to the regulator, means the regulator is leaking and should be replaced. Check the line for fuel or the smell of fuel.
To fully determine that you don't have a pressure drop off during actual WOT situations, you should tape the gauge to your windshield and take it for a test run. This will tell you if the pump can meet actual fuel flow demands at pressure and not just at a simulated WOT condition (as when removing the vacuum to the regulator).
When you have a gauge connected and the pressure looks initially good and then bleeds off quickly when you shut the engine off, you can do a couple of tests to help you figure out where the pressure loss is.
What the factory manual says to temporarily install, is a set of "fuel line shut off adapters" (probably something the normal guy is not going to have available). You remove the fuel lines from the rail and connect these valves in between. This lets you shut off either side of the lines for testing.
You can do the same thing by pinching the flexible lines to shut them off, but risk breaking them. You might be able to do it (your risk) by using a needle nose vise grips and putting some scrap hose as cushions on the jaws. Then use that to clamp off the line just enough to seal it. Obviously, this is not the best way to shut off the lines and could result in breakage. Heat and age can make the hoses brittle. If you don't want to risk it, don't. It's just a suggestion.
You can use the fuel pump prime connector for pressurizing the system (jumper 12v to it to run the pump).
Watch your gauge as you jumper the prime connector. When you have good pressure remove the jumper and clamp off (or use shut off valve) the fuel supply line (3/8 pipe). If pressure holds, you have a leak on the feed line somewhere before it gets to the clamp (or shut off valve) or at the check ball in the pump. If it still goes down, release your clamp (or open shut off valve). Pressurize the system again, then remove the jumper and this time clamp (or shut off) the return line (5/16 line). If pressure holds, then the regulator is faulty. If pressure does not hold, you need to locate leaky injector(s). If you can't tell a leaky injector from reading the plugs, you can look and see if injectors are leaking by removing the fuel rail screws and pull the rail and all the injectors up, so you can see under them. Leave them over the injector ports. Pressurized the system and look under the injectors to see if any are dripping.

(I) test the injectors first, remove the regulator and plug the fuel rail, if the fuel pressure dropping off problem stops with the fpr removed its a defective pressure regulator if it continues its very likely a defective injector(S) if they (injector(S) minus the FPR) hold steady pressure testing the FUEL PRESSURE regulator next, is pointless ,its defective, if the fuel pressure dropping off problem starts again once its reinstalled its a defective pressure regulator

HOME DEPOT sells rubber corks, and you hold them temporarily in place for testing with a vise grip

if its defective replace it with an adjustable version




IVE generally found no problem with any corvette LT1 or TPI efi if it will quickly build a minimum of 38-40PSI on start up and MAINTAIN at LEAST 38-40 psi for a MINIMUM of 10 minutes after the engines turned off, 40-42 lbs is what the factory tests want and expect so if your getting 38-40psi your pressure readings indicate a normal, perhaps even better than average pressure reading, and more than expected pressure retention,
IF you suspect a TPI has a defective injector that's leaking or not flowing fuel,or partly clogged...You can also test this, to a degree, with a fuel pressure gauge
you can install a fuel pressure gauge on the fuel rail, and turn on the ignition key then watch the gauge, it should jump to 37-42 psi then remain fairly steady for at least 5 minutes before gradually loosing pressure.
If you can - and this is a pain in the butt to do, temporarily- remove the injectors. Leave them on the rail, but remove the rail. from the intake itself, This requires removing the majority of the TPI (P.I.T.A. but required).
yeah. a good quality and properly adjusted, adjustable fuel pressure regulator is generally going to potentially provide,
just enough more consistent fuel delivery volume to be worth a few extra hp, but its major benefit is in the fact in many cases,
it can easily result in 30- plus hp over a improperly functioning O.E.M, fp regulator. (not all that rare)
keep in mind theres a huge difference between replacing a fully functional O.E.M. fuel pressure regulator ,
with an aftermarket adjustable regulator ,
which may or may not provide any benefits and replacing,
a mal functional, O.E.M. fuel pressure regulator with an aftermarket adjustable regulator ,


Dyno Comparisons -- Adjustable Fuel Pressure Regulator Settings


Here, the dyno shows a 16.6 horsepower and 14.6 ft/lbs torque difference between the stock fuel pressure (46psi) and 36psi with the LG Motorsports adjustable regulator. Actually, it was still making more power at 35psi than 36psi, but until I can measure my O2 sensors, I did not want to lean it out any further. The average gain here was 13.9 horsepower and 15.4 ft/lbs torque. Check out the Dynojet Race Routine between the stock and 36psi fuel pressure.

Something new: Dynojet is currently Beta testing their new WinPEP software for the dyno. With this software, they have the ability to graph up to 12 graphs at once. Check out the Dynojet WinPEP Graph of all the power between the stock and 35psi fuel pressures.

NOTE: One thing that I have found after some time with this mod is that the stock computer is quite smart. After lowering fuel pressure to achieve a better air/fuel ratio, the computer sees this at part throttle and adds injector pulsewidth to compensate. Basically, horsepower fell back off to where I started from. While normal trains of thought tell us that since O2 values are not measured during wide open throttle, that fuel pressure should have a long lasting effect here. Actually, it does not. The computer uses the last known long term fuel trim integer at WOT, which is to add fuel since at part throttle it has adjusted for being too lean.
related threads









Remove the rail, but leave it connected to the fuel lines.

Next up, put a strip of cardboard under each bank. Then, have a buddy turn the ignition key on but not try to start the engine , you should hear the fuel pump run for 3 seconds while you look to see what happens. You should get an immediate spray of fuel.(all should be about equal and no injector remains dripping fuel) now have your buddy Turn off the key, while you watch closely to see which injectors are leaking.

Intake Air Temp sensor. It is located on the bottom of the inlet plenum a few inches ahead of the distributor. It is like right next to the fuel pressure regulator., it can effect fuel flow rates



1987 TPI

1991 TPI

basic fuel injector test

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


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


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

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








Last edited by a moderator:


Staff member
Ive got oil leaking steadily from the rear of the engine intake area, and the fuel pump runs for 4-5 seconds then quits? any ideas??



if you hear the fuel pump pressurize the fuel rails but the engine only starts than stalls, or fails to start, its frequently the fault of a defective oil pressure sensor

if you don't have fuel pressure in the fuel rail check the fuel pressure regulator

low oil pressure or a defective oil pressure sensor will cut off your ignition

both these sensors, located near the base of the distributor on the block, are known to fail & leak,oil at times, especially the smaller one with two blade connectors

the first thing Id check is the oil pressure is reaching and maintaining at over about 10 psi with a separate gauge, the fuel pressure cuts off if the oil pressure drops below about 5-6 psi (yeah I know it says 4 psi BUT that's in an ideal world, in some cases it takes up to 9 psi with a sticky switch)

remember this part
"When you start an L-98 engine Corvette, a series of events take place that causes the engine to run. Knowing the sequence will help you troubleshoot no start conditions.

Fuel Rail Pressurization:

When you first turn the key to the “on†position, the fuel pump will run for 2 seconds pressurizing the fuel rails. There is a Shraeder valve on the passenger side fuel rail near the rear of the engine and if you measure the pressure there after the pump runs, you should see between 40-42 pounds of pressure. The reading will go to 38-40 pounds nominal once the engine is running.test by attaching a fuel pressure gauge to the fuel rail at the shrader valve, on TPI and LT1 engines its located on the pass side fuel rail

Initial Crank Action:

If you then rotate the key to the start position (assuming the anti-theft system has not disabled the starter), the engine will rotate.

Once the oil pressure has reached 4 PSI, the oil pressure switch will close allowing the fuel pump to run. (Note that you should have a black oil pressure switch/sender. It is mounted behind the distributor on the driver’s side and if it is not black, it is suspect due to a run of bad units that stayed in the GM parts pipeline for some time). "

btw those oil pressure switchs are a known source of problems, they get deffective, intermittently,at times, they get oil leaks and they just start doing crappy connections at times, ID replace it even if its supposed to be newly replaced, or at a minimum Id get out a V.O.M. and check its opperation durring the start/run procedure, but thats a p.i.t.a. Id replace it and check the connections and wireing.

If thats not the cause Id be looking at the fuel pressure regulator diaphram it may be leaking and need replacing, better still install a adjustable fp regulator, the pump itself may be defective, allowing the fuel to flow in reverse once it stops, you might have a injector thats leaking (constantly stuck open)

this should help also



as to the oil leak, its a safe bet its the oil pressure sensor or its connections to the block,or the intake rear seal, replace the sensor, if that does not cure it the intake gasket most likely needs to be replaced.

http://www.ecklers.com/search.asp?action=freeSearch&free_text=oil pressure sensor&yearConstraint=1985&searchHistory=


it helps if you understand that oxygen sensors do not measure your true fuel air ratio,entering the engine, but instead measure the remaining oxygen content of the burnt exhaust gases,and there are both narrow and wide band sensors


reading thru these links, and sub links might prove useful
running LEAN generally is caused by a vacuum leak or loose seal on an intake gasket or sensor malfunction, running rich is generally related to a mal -functioning injector, fuel pressure regulator or sensor, especially oxygen and temp sensors , but failure to correctly adjust the IAC, and TPS sensors are a common cause, get out your shop manual,and check your fuel rail pressure and fuel pressure regulator function, then pull trouble codes as a first step, reading the spark plugs and verify the ignition advance and injector fuzes and pulse duration, and verify the exhaust and catalytic converters are functioning correctly would be checked next, for good indicators of the cause of a less than ideal fuel air ratio.







Last edited by a moderator:


Staff member
sometimes the answers so obvious we don,t want to see it!
Im always amazed at the guys that don,t
break out the shop manual ,

GET out the multi meter, and a fuel pressure gage,
and do a few quick tests for loose electrical connections, look for vacuum leaks and consistent fuel pressure on the fuel rails
and verify the alternator voltage is at or above 13.5 volts,

when things don,t run correctly and the guys that don,t
pull the trouble codes, they are skipping a step that may waste hours





my neighbors kid just purchased a 1987 camaro from some other kid, the car runs like crap,hard to start,ran rough, stalled, cut out frequently, etc. and after a few tests we get down to measuring the sensors, and I find the manifold temp sensor is reading off the scale open,the fuel filter looks like its 10 years old minimum as its well rusted, and 5 if the 8 fuel injectors don,t read anyplace close to the ohms range they should, 2 are dead open reading off the scale open, and 1 reads 57 ohms two read in the 25-30 ohms range
I also find the intake has vacuum leaks, I point those things out and strongly suggest he buy new intake gaskets, a manifold temp sensor and a new set of 24 lb injectors, naturally the kid wants to try some injector cleaner as hes on a limited budget, I tell him it can,t hurt but its also unlikely to help.
I tell him to get on the internet and start shopping and look for a new set for under $350, but don,t buy anything until I check it out!
he will need to check all the sensors and the O2 sensor is suspect
infrared thermometers are a very useful tool to track down issues with tuning, or mal functioning sensors


below youll find several links, and sub links,
that may take you several hours to read through,
but it will save you a great deal of time and money to do so carefully.
read through all the linked info it contains a good deal of related info youll need to look through and understand to boost the TPI engines power effectively.
Knowing what your dealing with, what the stock parts can do, and what should be modified or replaced, and what you can do to enhance , increase and broaden, the power is 1/2 the battle here.
(take notes and ask questions)



A visual inspection tool that easily fits thru a spark plug thread hole is valuable at times

GOOGLE PV-618 and PV-636




a leak down tester is always a good test tool to have access too


If your injectors are leaking, injectors obviously should be under the control of the CPU and should not remain fully open to drip fuel constantly.
carefully visually inspect your cars wire harness for corrosion ,loose or broken or shorting connectors or wiring, obviously getting the wrong electrical pulse, a grounded or shorted connector will cause problems. visually inspect each injector pigtail for loose broken or shorted or grounded connectors or wires
first verify your getting a pulse at each injector and you have 38-42 psi at the fuel rail shrader valve.
its as usual a case of isolate and test , if the injectors are stuck open the injectors defective or its in need of a careful commercial professional cleaning, verify if its the injector or the injector control pulse duration



replacement injector pig tails are available at rock auto for less than $5 each







http://www.harborfreight.com/cpi/ctaf/d ... mber=93547







BTW remember those cheap crappy fuel filters I told you to never use

well heres where they come in handy, you plug them into the rubber fuel line between the vacuum gauge and the intake plenum where they act like a pulse dampers making the vacuum needle stay a bit more steady and easier to read


http://www.harborfreight.com/5-in-1-dig ... 98674.html


obviously the basics always apply ,
you need to think carefully, don,t assume anything.
Id suggest pulling trouble codes and verifying the basics of engine function,
are you actually getting spark at ALL the plugs?
are you getting injector pulse from the injector wire harness, do you have fuel pressure?
have you been checking the too verify your actually getting fuel out of the injectors,into the cylinders?
are all the fuses in the panel good?
have you verified that your alternator produces 13.5 plus volts,
that your getting spark at all the spark plugs ,have you verified the spark plugs are actually arcing and not fuel fouled?
your getting compression in all cylinders, all the rockers move, as the engine rotates?
ALL the sensors are fully functional,
your getting at least 10 psi of oil pressure as the engine spins while its trying to start,
you need to see the fuel pressure is consistently at 38-42 psi.
you need to verify the fuel filter and fuel pressure regulator and return line are functioning as designed.
verify all the electrical grounds are good,
and you use a noid tester to verify your getting the injector pulse.
what most people fail to do is test and verify, you can,t assume anything.
youll want too verify, youve got no plenum or runner vacuum leaks, and the catalytic converters are NOT restricting exhaust flow, theres no excessive exhaust system back pressure.
just because the injectors have pressure in the fuel rail, and get a pulse does NOT insure fuel flow thru them,
and having fuel rail pressure does not insure ITS GOOD fuel,
it can be tainted with water or rust particles in the fuel,

preventing fuel atomizing in the cylinders.
clogged catalytic converters can easily cause the engine to fail to flow air,

checking the plenum vacuum and exhaust back pressure and reading the exhaust fuel/air ratio,
use of an infrared temp gun, to verify cylinder exhaust temps are reasonably equal and a multi meter to set the TPS sensor and verify the ignition wire resistance will help.
simple stuff like verifying the firing order that you just know is correct (which may not be , so VERIFY IT) get over looked
and testing the coil and oxygen sensors and temp sensors sure helps.
After you verify theres consistent strong electrical spark at the spark plugs when your trying to start the engine and fuel pressure is consistent at the fuel rails,and your getting at least 7-8 psi of oil pressure,
IF you suspect a fuel delivery related issue, a good long spray of starter fluid into the throttle body and trying to start the engine with that extra fuel source may prove informative, if it trys to start with the extra fuel in the plenum but failed to start without it, its a good indicator the injectors are plugged or defective

if you suspect water in the fuel pull the inside of the shrader valve

with a valve tool, and slip 12 feet of braid re-enforced 5/16" pvc hose over the valve ,

clamp it with a screw clamp

on the valve so theres less chance of a fuel leak, and let the fuel pump push a 1/2 gallon of fuel out of the fuel rail into a clear glass container on the floor , allow it to settle for 15 minures and look for water to settle out of the fuel.












http://www.thirdgen.org/service-engine- ... rror-codes

http://www.iroczone.com/2009/10/1982-19 ... -firebird/

http://www.chevythunder.com/fuel%20inje ... pg%20B.htm









always drop back to basics
whats the compression test read on all cylinders?
WHAT cam are you running?(did you degree it in)
whats your ignition timing curve?
whats your fuel air ratio every 1000rpm?
whats the exhaust back pressure at every 1000rpms?
Have you tested for vacuum leaks?
what the intake vacuum reading in the plenum at every 1000rpms?
where in the rpm range does the power seem to start and drop off?
how did you adjust the valve pre-load?
whats your battery voltage?
what colors the ignition spark?
have you CAREFULLY VERIFIED the firing order?
WHATS the ignition wire resistance?
Whats the spark plug gap?
can you post CLEAR CYLINDER LABELED PICTURES of your spark plugs?

without facts, you're verified from current testing, to work from, your spinning your metal wheels and wasting time guessing
once you know the basics theres more than likely more tests, that will need to be done, changes to ets,power valves accelerator pump cams ignition timing etc. but with a firm basis of facts, and eliminating areas that prove to be operating correctly, its simply a matter of testing, verification,isolation, and tracking down the cause and correcting the flaw, in the combo or tuning.
btw you do realize that the cam might require a different rear gear ratio to perform at peak potential?

RELATED INFO, yeah I know, theres a bunch, but reading the linked info will help you track down the source of your problem
















what your 100% sure is correct may not be!
I recently had a guy over to do a minor test & tune on his car,(name with -held due to protecting the guys good name )no hes not on this site hes a neighbor) (an 1985 vette) because it didn,t run very well, (It idled like crap,after a cam upgrade)now it had a fairly normal low rpm power curve but it failed to pull well after about 3500 rpm
he was convinced it was an injector issue and wanted me to test and replace the injectors if required, or that the cam he had installed was defective
I told him the first step was to DROP BACK TO THE BASICS
and verify everything as we proceeded
but he was 100% convinced he had done every step in the cam install correctly, and wanted me to concentrate on finding the defective injector(s).
step one
I verified his engines TDC on the timing tab and damper
(the result was that the damper marks were off by about 4 degrees) I asked if he had degreed in the cam (knowing the obvious answer)
then I installed an adjustable timing tab and told him he was required to buy a replacement functional damper
I suggested we adjust the ignition timing , and we got that correct to factory specs
I suggested we adjust the valves,(he was 100% convinced he had that correct)
well I pulled the valve covers which is not easy with the alternator in the way) and after adjusting them at idle found they were all over the map on preload, (some were 1/4 turn in from zero lash some were 1.5 full turns in) he had adjusted them by spinning the push rods between his fingers, feeling for resistance after seeing the intake valve close., and I noticed one valve spring was cracked,(replaced that but had to use a stock spring so I strongly suggested he buy a full new set, I looked up the correct part number (YEAH! I KNOW! the chances he,ll follow thru and buy and install them are about as good as my wife buying me a MISTRESS for my birthday)
once the valves and timing were adjusted I checked for fuel pressure and found, that the fuel pressure was 36 lbs but dropped rapidly if the engine was shut off, it turned out the 9th injector was leaky(luckily I had a spare from a salvage yard)
step five
I checked for vacuum leaks and found the lower left runners were not sealed correctly(that was corrected with a new gasket.
step six
I metered the ignition wires for resistance (they all sucked)and checked the firing order,(ok) looked over the rotor and distributor cap (absolute joke, corroded, (white crumbly aluminum contacts) looked to be several years old and evidence of getting wet at times) and verified plug gap (again they ran from .037-.051) I dropped them all to .043, now the car ran a good bit better, we discussed pulling the timing cover and verifying the cam timing but that's a good deal more work, so for now we will assume its close until we get the time to check
step seven
I started verifying battery voltage, fluid levels, and sensor connections , and found the o2 sensor wire had obviously been at least on occasion touching the exhaust in the past as it was floppy loose ,as the insulation was melted, and the knock sensor was not even connected as the wire that goes to it had no connector.

if you think this was a worse case deal its not!
most older corvettes I see and some I work on, come into the shop only after the owners get tired of chasing intermittent problems, or find that the car runs like crap and only then decide to research the cause.
look we all have problems,wear issues and most of us work on very tight budgets, but you can,t jump to conclusions or assume anything, the only way to correct problems is to drop back to the basics and VERIFY every thing STEP BY STEP,WITH A BASIC CHECK LIST and a few tools like a timing light, a shop manual and a MULTI meter are mandatory







the answers are in this thread and sub links, but Ill post info above


Here's some good reads for tuning carbs with an A/F logger:
http://www.innovatemotorsports.com/reso ... ileage.php
http://www.innovatemotorsports.com/reso ... g-hero.php

Here's a quote at the Innovate Motorsports website that inspired me:
"A carbureted engine can produce just as much horsepower as a fuel-injected engine. The trick is tuning. Probably the main advantage of fuel injection is its "tune-ability." With an LM-1 air/fuel ratio meter, and a little knowledge, any carburetor is tuneable."

Other links are here at the Innovate site:
http://www.innovatemotorsports.com/reso ... entral.php





http://para.noid.org/~lj/PCM Tutorial/PCMtutorial.htm






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