upgrading your TPI MAF and CPU links

grumpyvette · Feb 1, 2010

http://www.1aauto.com/mass-air-flow..._content=EAF&gclid=CO-WoOWzqMoCFZOCaQod8M0L2A

1985 - 1226870 ECM - Camaros, Firebirds, and Corvettes

Being the first year of production for the TPI system, there were some things that GM wanted to change almost right off the bat. This year was a MAF setup, and used the 1226870 ECM. This was an ECM in the C3 family (like a TBI ECM). This ECM was used only on 1985 models. It used a small box mounted right above the ECM called the Mass Air Burnoff Module. This ECM can be easily recognized by having the PROM access cover at the top of the unit, and has only two harness connectors.

This ECM was used both on 305 and 350 engines. Depending on the engine size however, it used a different PROM, and a different CAL-PAK. There is limited support for this ECM as far as PROM modifications. This does not mean that it is more difficult, or that PROM modifications can't be made. Its just that there hasn't been as large an effort to work on this ECM, enthusiasts often end up converting to a later model ECM. Also, it sends data to the ALDL port at 160 baud, which is very slow. This provides a "snapshot" of what all the sensors are reading once every few seconds. By comparison, the later TPI ECMs were 8192 baud. They sent data several times a second.

I have read on several occassions that late in the 1985 production run, GM had already changed to the ECM and harness that they later used in 1986. I have not confirmed this myself, so I can't say for sure that its true. If this is true though, it is possible though to come across a 1985 model which uses the 86-89 ECM.

1986-1989 - 1227165 ECM - Camaros, Firebirds, and Corvettes

This is the most common ECM which is used on MAF style setups. ECM number 16198259 is equivalent and can be used in its place without any problems. The same computer was used both for 305 and for 350 engines. The only difference between the two engine sizes was the PROM that was used. The Mass Air Burnoff Module that GM used in 1985 is no longer present. This model is part of the P4 ECM family. This ECM can be easily recognized by having the PROM access cover in the center of the unit, and has only two harness connectors.

Support for this ECM with regards to PROMs is much more common. Due to the nature of the MAF sensor, it is very easy to run a large or moderate cam without needing PROM changes. This system is not very sensitive to engine changes, and can adapt fairly well. However, many enthusiasts find that it is a little more difficult to fine tune than the later Speed Density system. Please realize that this is a matter of opinion and personal preference. Each of these systems have advantages and disadvantages over one another. ALDL data is sent at 8192 baud, much faster than the 1985 ECM. This allows for several sets of data per second.

1990-1992 - 1227730 ECM - Camaros and Firebirds

By far the most common ECM used on TPI conversions onto older vehicles. This is the later style Speed Density system. It does not use a Mass Air Flow sensor. Instead, a Manifold Absolute Pressure sensor is used in its place. This allows more flexibility in running air ducts to the throttle body, or an air filter can be installed directly on the throttle body. It is for this reason, that it provides a cleaner looking installation on many street rods, and hot rods. There are two equivalent ECM numbers which can be used in its place without any problems. These are numbers 16196344, and 16198262. This ECM is also in the P4 family. It mounts inside the passenger compartment, as it is not weatherproof. It can be recognized by having a very large PROM access cover that runs from one side of the ECM to the other, and has three harness connectors.

By far the most support for PROM work exists for this ECM. Most enthusiasts feel this is the easiest system to tune. However, it is also very sensitive to engine changes. Any change that affects the engines volumetric efficiency significantly (ability to fill the combustion chamber) will not show its true potential until the system has been tuned. Volumetric efficiency is affected mostly by cam and head changes. This does not mean that you cannot run a moderate or large camshaft with this setup. It only means that tuning is required to see the true potential of engine modifications. This ECM provides ALDL data at 8192 baud as well. This is relatively fast, as it provides several sets of data every second.

This ECM is internally the same as the 1227727. The only difference is that the 1227727 is weatherproof and can be mounted in the engine compartment whereas the 1227730 cannot. The PROMs will interchange between these two computers. Harnesses will not interchange, as the ECM connectors are very different.

1990-1991 - 1227727 ECM - Corvettes

This ECM is internally the same as the 1227730 mentioned above. The difference is that this one is weatherproof and can be mounted in the engine compartment. This is the later style Speed Density system. It does not use a Mass Air Flow sensor. Instead, a Manifold Absolute Pressure sensor is used in its place. This allows more flexibility in running air ducts to the throttle body, or an air filter can be installed directly on the throttle body. It is for this reason, that it provides a cleaner looking installation on many street rods, and hot rods. There are two equivalent ECM numbers which can be used in its place without any problems. These are numbers 16197128, and 16198260. This ECM is also in the P4 family. It can be recognized by the four large ECM connectors.

This ECM as well as the 1227730 can use each others PROMs. Due to this reason, there is plenty of support for PROM work available. Because this is a Speed Density system, most enthusiasts feel this is the easiest system to tune. However, it is also very sensitive to engine changes. Any change that affects the engines volumetric efficiency significantly (ability to fill the combustion chamber) will not show its true potential until the system has been tuned. Volumetric efficiency is affected mostly by cam and head changes. This does not mean that you cannot run a moderate or large camshaft with this setup. It only means that tuning is required to see the true potential of engine modifications. This ECM provides ALDL data at 8192 baud as well. This is relatively fast, as it provides several sets of data every second.

This ECM is internally the same as the 1227730. The only difference is that the 1227730 is not weatherproof and must be mounted inside the passenger compartment. Harnesses will not interchange, as the ECM connectors are very different.

links to info that may help

https://www.themotorbookstore.com/c...MIrei9nJqr7gIVD4iGCh3orQayEAQYAiABEgJUMPD_BwE

http://www.larryselectricsite.com/downloads/tpiinstructions.pdf

https://howellefi.com/wp-content/up...t-or-LT1-Fuel-Injection-Harness-1985-1992.pdf

https://www.hotrodhardware.com/inde...d=7157/category_id=1579/mode=prod/prd7157.htm

https://www.ronfrancis.com/images/TP30-INST.pdf

http://www.jimsperformance.com/tpibuy.html

https://www.hotrodhandbooks.com.au/eBooks/TPI/TPI On Line-03-1.html

grumpyvette · Feb 5, 2010

Re: upgrading your TPI MAF

the original chip,transmitted at only 160 BAUD, (INSANELY SLOW BY TODAYS STANDARDS)

http://www.eecis.udel.edu/~davis/z28/ecm_swap/870chart.pdf

http://www.gmtips.com/3rd-degree/dox/ti ... screen.htm

http://www.chevyhiperformance.com/techa ... index.html

the ECM that came in 1986-1989 TPI Fbody's and Vettes is a series 1227165 (165). The ALDL data rate in this model can supply diagnostic data at 8192 BAUD.

Understanding Block Learn Multiplier (BLM)

David Huinker

Introduction

In a nutshell, the Block Learn Multiplier (BLM) is the long term fuel adjustment that the ECM "learns" to keep the air/fuel ratio within acceptable parameters. The Integrator is the same idea, only for short term adjustments. Basically, these two strategies are used to make adjustments and adaptations to the ever changing loads, atmospheric conditions, and fuel quality to keep the car's air/fuel ratio correct for driveability and emissions.
Also, keep in mind that when we say Long Term or Short Term, we are talking in computer time, not human time. In our ECM the Long Term fuel adjustment (BLM) happens about twice per second, while the Short Term fuel adjustment (INT) happens about 20 times per second

What are "Cells"?

The fuel delivery strategy uses a two dimensional table that has four rows and four columns, for a total of 16 "cells". Each cell contains a Block Learn Multiplier (BLM) value (from 0 to 255), which represents a long-term fuel correction based on that cell's operating conditions over a relatively long period of time. Each BLM value in turn contains an integrator value (also from 0 to 255), which is a short term fuel correction based on immediate operating conditions. For both the Integrator and BLM values, a higher value represents a correction that adds fuel to the fuel mixture, due to higher injector pulse widths.

MAF / RPM	0-800 rpm	800-1100 rpm	1100-1500rpm	1500 +rpm
0 – 9 GPS	Cell 0	Cell 1	Cell 2	Cell 3
9 – 20 GPS	Cell 4	Cell 5	Cell 6	Cell 7
20 – 30 GPS	Cell 8	Cell 9	Cell 10	Cell 11
30 - + GPS	Cell 12	Cell 13	Cell 14	Cell 15

The table above depicts the BLM cell table that is held in the typical Turbo Regal ECM. As you can see, it is offset by rpm in the columns, and by airflow in the rows. The individual cells are numbered 0 through 15 (for a total of 16 cells). So, the cell being accessed at any given point in time is controlled by airflow versus rpm.
Let's take a few "for instances". Let's say the car is sitting in the driveway in Park, up to temperature, and just idling. In that case:

RPM = 750
MAF = 6

Since the RPM is very low and the MAF is very low, the car will be using the information in BLM Cell 0 to adjust the idle fuel mixture. The value contained in that cell is adjusted with the Integrator values (which change based on O2 readings, etc.).
Now, let’s go for a typical highway cruise, at about 65mph, on a nice flat road:

RPM = 1800
MAF = 22

Since the RPM is above the highest value in the column to the right, and the MAF is reading a value in the “third” row, we can see that the ECM is now accessing, and using the BLM value in cell 11. Cruise conditions will often move between cells 7 and 11 based on small changes in MAF, since the typical highway cruise value is between 15 and 25.
Typically when you pull away from a stop sign or traffic light in fairly normal circumstances, you’ll see that it takes only a second or so for the RPM to jump over the 1500 upper RPM limit, and the MAF (air flow) will very easily jump up over the 30 gps upper MAF limit. In this example the ECM will be using cell 15 (sometimes erroneously called the WOT cell) (WOT meaning Wide Open Throttle).

OK, So what's the BLM DO?

The BLM is a long term adjustment , which is stored pretty much permanently (unless you disconnect power to the ECM), to the fuel delivery calibration that results from the ECM "learning" the values while you are driving around. 128 is the ideal value, because it is the center point of the range 0-255. Above 128, and the ECM is adding fuel to compensate for a lean condition at a particular load and RPM. Below 128, and it represents a correction for a rich condition.

How does the Integrator play into this?

On a cold start the INT is set to 128 and kept there until the coolant reaches a threshold value, a timer says the engine has been running long enough, and the O2 sensor has warmed up and started responding. The ECM then sets the closed loop flag, which meansthat if other conditions are met (not in PE, DE, or DEFCO modes, primarily) the ECM uses the O2 sensor to control the INT. It adds to the INT in small increments until the O2 voltage goes above a threshold so the ECM knows the engine is now rich, then it starts subtracting from the INT until the O2 voltage goes below another threshold and the engine is lean. The ECM keeps cycling the INT, trying to keep the time spent rich equal to the time spent lean so it knows that the average is stoichiometric. If other conditions are met then the learn control flag is set and the ECM keeps a moving average of the INT values. If this average is not 128, it will add or subtract to the current BLM value to move the INT average towards 128. This is done a few times a second, without the INT ever having to get to an extreme value such as 90 or 150. The stock BLM range is 105 to 150, but even if the BLM has reached one of these limits the ECM is still able to keep the engine averaging stoichiometric so long as the INT is not also at a limit. For example, the BLM could be 150 and the INT ranging between 135 and 145.
If you have a scan tool or Direct Scan you can watch this process. The ALDL update rate will keep you from seeing all of the INT values but you will still see the long-term trends. Start the engine and let it warm up so that learn mode is enabled, then pull the vacuum hose off of the fuel pressure regulator. The fuel pressure will jump up 4-7 psi and the engine will go rich. The INT will drop below 128 and go down until the engine finally goes lean or a limit is reached, and will then go up and down over a range of maybe 10-20 units as the ECM keeps the engine bouncing between rich and lean, and the BLM will start dropping. As it does, the average INT will rise back to 128. Once the INT average is 128 the BLM will stop changing. Put the vacuum hose back on, the fuel pressure will drop, the engine will go lean, and the mirror image of the above will occur. The INT will rise, start bouncing up and down, the BLM will rise, and the INT average will eventually reach 128 and the BLM will stop changing again.

Summary

BLM values are divided in to "Cells" based on MAF vs. RPM. Within each cell, there typically values from 105-150 for the BLM. Within the BLM value, there are Integrator values, typically 105-150 also.
The Integrator is adjusted based on sensor feedback (primarily the O2 sensor) to make real time adjustments for varying conditions. If the adjustments cannot be made in a BLM value, then the BLM value is either increased (add fuel) or decreased (subract fuel) to compensate.
If you reach the "corner" of an individual cell and not further adjustment is possible, the car may not run correctly and there is a problem with the calibration or a critical sensor.
It all sounds very intimidating, but really isn’t. One must keep in mind that the changes that are being made, as in the INT for example it is happening at close to 20 times per second. Think of it this way; The INT is used to “drive” the BLM number toward a value needed to maintain stoiceometric A/F ratio. As in one of the examples above, make a radical change (such as removing the fuel pressure regulator’s hose) and watch the INT do it’s thing!! The INT will jump to a high value, and hover there while the BLM starts its “march” up the scale. As the BLM approaches the value needed to get the A/F ratio corrected you’ll see the INT value heading back down toward 128. Ideally, they will both meet at 128 at about the same time. It’s really neat stuff to watch.

grumpyvette · Jul 18, 2010

Here's some info I found on another site, maybe this helps;

How to Modify L98 Mass Air Flow (MAF) Sensor

WARNING
1. The sensor wire is FRAGILE, so handle the MAF with care..
2. NEVER run the engine without an air filter in place once the MAF screens are removed.

Backgroud
The MAF end screens and internal heat sink fins limit maximum air flow.
529 CFM - max. flow rate stock
711 CFM - max. flow rate with screens removed
750 CFM - max. flow rate with screens and cooling fins removed
Reference - TPIS "Insider Hints", pp 10.

Preparation
1. Disconnect the tubing connected to either end of the MAF.
2. Lift the MAF slightly and disconnect the signal/power from it.
3. Carefully but firmly clamp the base in a vise.

Remove End Screens
There is a cap glued to either end of the MAF that holds the screen assemblies in place.
1. Locate the groove separating the end cap from the MAF body.
2. Frimly run a sharp knife blade around this groove till you hear a crack.
3. It may be necessary to use a thin screwdriver blade and the knife to crack the
remainder of the glue that holds the end cap to the MAF.
4. Remove the end cap and use the knife point to pry out the screen ring.
5. Repeat for the other end cap.

Remove Cooling Fins
Within the MAF body there are 7 Al cooling fins projecting from the heat sink base and
a central tube which contians the delicate sensor wires.
1. Carefully cover each end of the center tube with duct tape to prevent accidental
damage to the sensor..
2. Insert a round silicon-carbide hack saw blade through the MAF body.
3. Cut each heat sink fin off as close to the base as possible. Use care not to scuff the
inner surface of the MAF body.
4. Remove the hacksaw blade and use a Dremmel to smooth the fin remnants..
5. Clean all debris and dust from within the MAF body.
6. Remove the duct tape that covered the center tube.

Reinstall MAF
1. Remove the modified MAF from the vise.
2. Carefully reattach the electrical cable to the MAF connector..
3. Reattach the front and rear air ducting and tighten the two clamps.

grumpyvette · Oct 8, 2011

http://www.mamotorworks.com/corvette-c4 ... 6-893.html

the 1985-91 TPI corvettes used a MAF sensor, the LT!-LT$ vettes used a different MAP SENSOR

https://www.ebay.com/itm/MAP-Sensor...T4-GM-Repair-Connector-Wire-TPI-/151403313601

https://www.ebay.com/itm/MAP-Sensor-Connector-Pigtail-Harness-93-97-LT1-LT4-GM-Repair-Connector-Wire-TPI/192197612559?_trkparms=aid=222007&algo=SIM.MBE&ao=2&asc=20160323102634&meid=832c05b2dde84f84a66b76036e9771d1&pid=100623&rk=2&rkt=6&sd=151403313601&itm=192197612559&_trksid=p2047675.c100623.m-1

http://garage.grumpysperformance.co...-auto-elecrtrical-connectors.3105/#post-68805

http://www.corvettemods.com/Corvette-C4 ... _6306.html
http://www.digitalcorvettes.com/forums/attachment.php?attachmentid=23105&d=1527530116

RELATED INFO
viewtopic.php?f=32&t=661

http://www.corvettefever.com/tipstricks ... index.html

http://corvette-parts.zip-corvette.com/ ... f%20Sensor

http://www.wellsve.com/sft503/Counterpoint3_2.pdf

http://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/how-to-test-the-maf-sensor-1

Suggested Installation Instructions for:
601-096, Mass Air Flow Sensor Test Tool
INTRODUCTION:
The Mass Air Flow Sensor (MAF) is a form of â€œhot-wire anemometerâ€ that measures air volume
and density. It produces a frequency output. A constant voltage source is applied to the hot wire.
The wire has a positive temperature co-efficient meaning, that as it gets hotter its resistance
increases. The incoming air tends to cool the wire, lowering its resistance thereby increasing the
current. Hot dry air, being less dense (and having less mass), cools it less than cool moist air that
is more dense (and has more mass). The greater the air masses passing the hot wire the greater the
current flow. A circuit mounted on the top of the MAF sensor converts the current flow into a
square wave whose frequency changes depending on the mass of the air flow.

MAF (Mass Air Flow) Sensor. Front of engine ahead of throttle body. .4 Volts @ idle, 5 Volts @ Full Throttle.

INSTALLATION AND TEST PROCEDURES:
1. With ignition switch â€œOFFâ€, disconnect the ECM connector from the Mass Air Flow Sensor.
Refer to the GM Shop Manual for sensor location.
2. Plug in the MAS-1 Test Tool connector into the Mass Air Flow Sensor. Plug the MAS-1 Test Tool
pins into the ECM connector. Take care to insure each pin location on the MAS-1 coordinates
with the same pin location on the ECM connector, i.e., A to A, B to B, C to C, etc. Stamped on
the connector body are letters A through E. CAUTION: DO NOT reverse the pin configuration.
DO NOT force test jumper into connection. Damage to pins or sensor may result. DO NOT allow
pins to touch. Carefully move test jumper from side to side to align pins into place.
3. Take voltage measurements by using a digital voltmeter (10 megaohm impedance required) by
touching the MAS-1pins. The ignition switch may be on or off depending on the type of test.
4. Voltage may vary depending on make and model. Refer to the GM Shop Manual for proper
voltage readings.
5. Remove the MAS-1 Test Tool and re-connect the ECM connector to the Mass Air Flow Sensor.

I found these bits of info

tequilaboy said:
Here's a plot to illustrate the pw limitation for constant flow of 255 gm/sec assuming a stoich AFR of 14.73:1. This will give you an idea of the excess air that can be supported via PE tuning alone with a pegged MAF at mid-high rpm. Pegging at low-mid rpm is unlikely, but could be a concern for a very large displacement or turbo car.

For this condition (pegged MAF for all rpms), AFR targets below (richer than) the dark blue line (or richer than the yellow line below 3800 rpm intersection point) will not result in any additional enrichment, since the pw will be internally limited.

The medium blue line represents the richest AFR target that you can achieve by tuning the PE vs coolant temp and PE vs rpm tables. This is approx. 5.89:1.

Note: This plot alone doesn't tell the whole story, the pw limitation can also come into play below approx. 4,000 rpm if the MAF flow should exceed the dark blue line of death. This plot is based on a fixed 12.8 target AFR. Richer or leaner targets will skew the resulting curve.

Note: This post is intended to give 86-89 MAF users an idea of what can be achieved via traditional PE tuning methods only. These limitations can be overcome with MAF upgrades and/or special tuning. This does not reflect an overall limitation of a MAF based system.

Chart A-1 Chart A-2 Back to troubleshooting Flow chart index

Lemme said:
Found this equation on how pulse width (pw) is calculated for an efi controlled engine. May be able to relate it to the c4 ecms calcs

http://en.wikipedia.org/wiki/Fuel_injection#Sample_pulsewidth_calculations

pw ms = (air lb/min)/(rpm*strokes per rev*afr*fuel lb/min)*1000*60

Example at idle for 350 ci
air lb/min = 1.03 (approx 8 g/s)
rpm = 700
strokes per rev = 2
afr = 14.73
fuel lb/min = 0.37(22 lb /hr injectors)

Substituting in values gives pw ms = 8.4 ms Actual bpw from datalog = 2.23ms

Example at 5000 rpm for 350 ci
air lb/min = 28.42 (approx 215 g/s)
rpm = 5000
strokes per rev = 2
afr = 14.64
fuel lb/min = 0.37(22 lb /hr injectors)

Substituting in values gives pw ms = 32 ms Actual bpw from datalog = 10.23ms

Interesting that this formula seems to be giving pulse widths 3 times that of my 87! Does the batch fire system fire more than once per cycle?

Grumpy · Jan 11, 2016

https://www.hotrodhandbooks.com.au/eBooks/TPI/TPI On Line-03-1.html

read related links and sub-links
http://garage.grumpysperformance.co...-auto-elecrtrical-connectors.3105/#post-68805

http://garage.grumpysperformance.com/index.php?threads/testing-1985-89-m-a-f-sensor.1475/#post-43635

http://garage.grumpysperformance.co...s-air-flow-vs-speed-density.11952/#post-56852

Grumpy · Jan 11, 2016

http://www.chevythunder.com/maf_code_33.htm

http://www.superchevy.com/features/153-0401-inuction-repair/

http://tpiparts.net/85_89_maf_sensors/

https://www.rockauto.com/catalog/raframecatalog.php?carcode=1041220&parttype=5128

http://www.jegs.com/p/Granatelli/Gr...1&cadevice=c&gclid=CMyZspOUo8oCFQaraQodbPUHAQ

youll find many guys claiming that aftermarket CPU chip upgrades help a great deal
Ive found some help marginally but many actually hurt performance
http://www.iroc-z.com/articles/articlepages/1990-3Chips Article by Cliff Gromer, Super Stock, 1991.htm

85-89 MAF TPI Systems

Below is a list of all the needed sensors to install a MAF TPI setup, and each of their functions.

Mass Air Flow (MAF) Sensor: This sensor is responsible for measuring air volume and density. It is located in the air duct, before the throttle body. All of the air that the engine consumes must first pass through the MAF sensor. At the center of the MAF, is a very thin wire whose resistance increases as it goes up in temperature. A constant voltage is applied to this wire. Air being drawn through the MAF has the effect of cooling this wire, which lowers its resistance, and increases current. As you might suspect, the more air is drawn through the MAF sensor, the greater the current flow. It is important to note that hot dry air is less dense and has less mass than cool moist air. As a result, hot dry air will cool the wire less than cool moist air.

A circuit mounted on the MAF sensor serves to convert the current flow into a variable frequency square wave on 1985 models, which is sent to the ecm. MAF units from 86-89 models output a simple analog signal instead of using frequency modulation like the 1985 units. The ecm will calculate the amount of fuel needed depending on the signal from the MAF sensor. It is very important that there are no air leaks (from a ripped air duct for example) between the MAF and the throttle body.

Oxygen Sensor: Responsible for determining the amount of oxygen in the exhaust manifold. Depending on how much oxygen is in the exhaust, the ecm can determine whether or not the air/fuel mixture is rich or lean. The signal sent to the ecm by the ecm varies between 0.0 and 1.0 volts. An ideal mixture (also known as a Stoichiometric mixture) of 14.7:1 is represented by .450 volts. If the oxygen sensor voltage is below .450, then the air/fuel mixture is lean. Anything over .450 means the mixture is rich. Since the sensor is essentially just a switching device, it will be fluctuating alot between lean and rich. This is normal, and an indication that the sensor is in working properly.
Keep in mind however that oxygen sensors (except wideband oxygen sensors), are not very accurate below or above .450 volts. Exhaust gas temperature will affect the oxygen sensor reading as well. The sensor will not read properly until exhaust gas temperature reaches approximately 600 degrees Farenheit. If you have headers installed, it is a good idea to use a heated oxygen sensor (3 wire) instead of the usual single wire sensor. Headers usually place the oxygen sensor further down the exhaust stream, where exhaust temperatures are cooler. A heated oxygen sensor will heat itself, allowing a more reliable sensor reading than a single wire sensor. If you have factory exhaust manifolds, then the single wire sensor is adequate.

Oxygen sensors are a regular maintenance item, and should be replaced every 30,000 miles. When an oxygen sensor goes bad, it tends to read lean, and will not fluctuate very much. The ecm will attempt to correct this false lean condition by richening the mixture. This will cause poor driveability, and high gas consumption.

Knock Sensor: Also known as detonation sensor, it is responsible for sensing spark knock. Basically, thats when the fuel mixture ignites before the spark plug fires. The piston is moving upwards as this premature combustion takes place. Since fuel is used to cool down the combustion chamber, a lean condition causes the temperature to rise, and ignites the fuel mixture prematurely. This is very abusive on the engine internals, and reduces the life of any engine. The more powerful the engine, the greater the potential for damage. Detonation can be cause by a variety of things. One of the more common causes on TPI retrofits where prom changes have been made to the fuel or spark tables is a lean condition. It isn't always loud enough to be heard, so just because you don't hear any pinging, doesn't mean its not happening.
Detonation will cause a vibration to travel through the engine block. The sensor listens for this vibration at a certain frequency, and sends a signal to the ecm when the frequency is heard. This frequency is different depending on engine size. To prevent possible engine damage, the spark timing needs to be retarded when detonation is present. The sensor itself does not pull the timing back however. The ecm is in charge of retarding the timing, and will do so according to a series of settings inside the prom. The knock sensor is located on the passenger side of the engine block on factory applications. It can however be relocated to the driver side of the block if needed (header clearance for example). They are different depending not only on the size of the engine, but also the ecm being used. It is important that the correct sensor is used to avoid problems. Although it is possible to run the car without one, I strongly suggest against this. I have had customers come to me looking for a $45 knock sensor after spending several hundred dollars and an extra month of work rebuilding a blown engine due to detonation.

Throttle Position Sensor (TPS): Responsible for reporting to the ecm the position of the throttle blades. The ecm will receive a signal which can vary from 0.0 to 5.0 volts. At idle, the TPS should be read .54 volts (factory specification) unless it has been set to a different value inside the prom. If it does not read .54 volts and the idle TPS voltage setting has not been modified in the prom, then it should be adjusted. Under full throttle, it should output close to 5.0 volts. Throughout its range of motion, the voltage should climb steadily, without any jumps or falls. If it is not steady or has some fluctuations as it is moved through its range of motion, it should be replaced. This sensor is located on the passenger side of the throttle body.
Coolant Temperature Sensor (CTS): This is basically a thermistor (means that it changes resistance with temperature) that supplies the ecm with the temperature of the engine coolant. This temperature reading is used for several important functions. The most notable is that the ecm adds extra fuel to an engine when its cold, and as the engine warms up, the extra fuel is reduced. This sensor mounts at the front of the intake manifold. The chart below shows the approximate resistance for this sensor in relation to temperature.

Intake Air Temperature Sensor (IAT): This sensor is also a thermistor (means that it changes resistance with temperature) that supplies the ecm with a temperature reading of the air being drawn into the engine. It is the same as the coolant temperature sensor on 86-92 models. The 1985 intake air temperature sensor used a different connector and cannot be used as a coolant temperature sensor because it had an exposed bulb. This sensor mounts underneath the plenum. The chart above shows the approximate resistance for this sensor in relation to temperature.
Idle Air Control (IAC) Valve: Although this is technically not a sensor at all, people often treat it as one. It is responsible for regulating the amount of airflow being admitted into the engine to adjust engine speed, particularly at idle and deceleration. The ecm controls the IAC at its discretion. The IAC works by moving a cone shaped pintle, which can extend and retract as needed to admit or block off incoming air. The valve moves the pintle in "steps". These steps are numbered and range from 0 to 160. A properly adjust throttle body should be idling when warm between 15-25 steps.

The IAC is used under a variety of conditions, not only at idle speed. The valve mounts on the bottom coolant plate of the throttle body.

Vehicle Speed Sensor (VSS): This is responsible for providing the ECM with the vehicle speed. It can be located either at the tailshaft of the transmission, or behind the speedometer on cars with a cable driven speedometer. It sends a 2k ppm (pulse per mile) square wave signal, and is needed for a variety of functions. It is absolutely critical for the ecm's learn mode, timing retard, emissions, torque converter lockup (automatic lockup transmissions only), idle speed control, and to avoid stalling on deceleration. It is possible to run without one. However, your car will NOT be street legal if you are required to retain emissions equipment, the ecm will not control the torque converter lockup, the ecm will not retard timing if you run into detonation, and it is possible to run into stalling /idle speed issues. In addition, the ecm will not adjust the fuel table properly as you drive (known as its "learning ability"). If the ecm does not know the vehicle speed it is assumed to be 0 mph.

If you still insist on not running a vss, I very highly suggest that the minimum vehicle speed for timing retard be brought down to 0 mph in the prom. The factory setting is 2 or 3 mph. If you don't bring this value down, and you do not run a vss, the ecm will NOT retard your timing under detonation.
https://www.zip-corvette.com/85-89-high-performance-adjustable-maf-sensor.html
85-89 High Performance Adjustable MAF Sensor

https://www.hotrodhandbooks.com.au/eBooks/TPI/TPI On Line-03-1.html

Item Number: EH-521

heres a rather useful addition to the older c4 corvette tuning world, its a new (yes expensive)
but adjustable and thus some what tune-able MASS AIR FLOW SENSOR for the TPI corvettes

Grumpy · Mar 8, 2019

https://www.zip-corvette.com/85-89-high-performance-adjustable-maf-sensor.html
85-89 High Performance Adjustable MAF Sensor

Item Number: EH-521

heres a rather useful addition to the older c4 corvette tuning world, its a new (yes expensive)
but adjustable and thus some what tune-able MASS AIR FLOW SENSOR for the TPI corvettes

Grumpy · Aug 21, 2019

http://www.blowerworks.net/

one major restriction to and TPI system running a stock MAF sensor is they are rather airflow restricted
due too both design and internal size, http://www.blowerworks.net/ sells custom 3" 3.5" and even 4" custom built MAF sensor designs,
obviously youll need a set of 30lb-50 lb injectors to keep up with the potential increased air flow and the controller that will also work with the custom parts

upgrading your TPI MAF and CPU links

grumpyvette

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Grumpy

The Grumpy Grease Monkey mechanical engineer.

Grumpy

The Grumpy Grease Monkey mechanical engineer.

Grumpy

The Grumpy Grease Monkey mechanical engineer.

Grumpy

The Grumpy Grease Monkey mechanical engineer.