Author Topic: GM TBI  (Read 1507 times)

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GM TBI
« on: October 29, 2014, 10:48:45 AM »
I figured I could put all my TBI info in one place.

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Re: GM TBI
« Reply #1 on: October 29, 2014, 10:49:42 AM »
MODES OF OPERATION:

The ECM uses voltage inputs from several sensors to determine how much fuel to give the engine. The fuel is delivered under several conditions, called "Modes." All modes are controlled by the ECM, and are described below.

Starting Mode:

When the ignition is first turned ON, the Electronic Control Module (ECM) turns ON the fuel pump relay for two seconds, allowing the fuel pump to build up system pressure. On Heavy Duty models, a fuel module will override the ECM two second timer and the fuel pump will run for twenty seconds and then shut OFF if the vehicle is not started. This circuit corrects a hot restart (vapor lock) during high ambient temperature conditions. If the engine is immediately started, the fuel pump will continue to operate. If the key is left in the ON position, but the engine is not started, the ECM will turn the pump OFF. The fuel pump will remain OFF until the ECM detects the crank signal, or in the case of a faulty fuel pump relay, the oil pressure switch detects approximately 4 psi of oil pressure which will then bypass the fuel pump relay.

Fuel delivery from the injectors (which deliver fuel in all operating modes) is controlled by changing the amount of time the injectors are turned on or "pulsed" by the ECM. The ECM checks the Coolant Temperature Sensor (CTS), Throttle Position Sensor (TPS), and the crank signal, and determines the proper air/fuel ratio for starting. This ranges from 1.5:1 at -36°C (-33°F) to 14.7:1 at 94°C (201°F).

Clear Flood Mode:

If the engine floods, it may be cleared by pushing the accelerator pedal down all the way. The ECM then pulses the injector at a 20:1 air fuel ratio. The ECM holds this injector rate as long as the throttle stays wide open, and the engine speed is below approximately 600 rpm. If the throttle position becomes less than approximately 80%, the ECM returns to the starting mode.

Run Mode:

The run mode has two conditions, called OPEN LOOP and CLOSED LOOP.

Open Loop:

When the engine is first started, and engine speed is above 400 rpm, the system goes into OPEN LOOP operation. In OPEN LOOP, the ECM ignores the signal from the Oxygen sensor, and calculates the air/fuel ratio based on inputs from the coolant temperature and Manifold Absolute Pressure (MAP) sensors.

The system will stay in OPEN LOOP until the following conditions are met:
1.   The oxygen sensor has a varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature)
2.   The coolant temperature is above a specified temperature.
3.   A specified amount of time has elapsed after starting the engine.
Closed Loop:

The specified operating conditions vary with different engines, and are stored in the programmable read only memory (PROM). When these conditions are met, the system goes into CLOSED LOOP operation. In CLOSED LOOP, the ECM calculates the air/fuel ratio (injector on-time) based on the signal from the oxygen sensor. This allows the air/fuel ratio to stay very close to 14.7:1.

Acceleration Mode:

The ECM responds to rapid changes in throttle position and manifold pressure or air flow, and provides extra fuel.

Deceleration Mode:

The ECM responds to changes in throttle position and manifold pressure and reduces the amount of fuel. When deceleration is very fast, the ECM can cut off fuel completely for short periods.

Battery Correction Mode:

When battery voltage is low, the ECM can compensate for the weak spark by:
1.   Increasing the amount of fuel delivered.
2.   Increasing the idle speed.
3.   Increasing the ignition dwell time.
Fuel Cut-off Mode:

No fuel is delivered by the injector when the ignition is OFF. This prevents dieseling. Also, fuel is not delivered if no reference pulses are seen from the distributor, which means the engine is not running. This prevents flooding. Fuel cut-off also occurs at high engine rpm, to protect internal engine components from damage
Testing and Inspection   


NOTE: A fuel system pressure test is part of several of the Diagnostic Charts and Symptom Checks. To perform this test, follow this procedure:

FUEL PRESSURE TEST
1.   Turn engine OFF to relieve system pressure.
•   
o   Disconnect negative battery terminal to avoid possible fuel discharge if an accidental attempt is made to start the engine.
o   Loosen fuel filler cap to relieve tank vapor pressure.
o   The constant bleed feature relieves fuel pump system pressure when the engine is turned "OFF".
1.   Uncouple fuel supply flexible hose in engine compartment. Install fuel pressure gauge between steel line and flexible hose.
2.   Tighten gauge in line to insure no leaks occur during testing.
3.   Connect negative battery terminal and START engine and observe fuel pressure reading. It should be 62-90 kPa (9-13 psi). If not, refer to DIAGNOSTIC CHARTS/FUEL SYSTEM PRESSURE TEST (CHART A-6).
4.   Turn engine OFF to relieve system pressure.
•   
o   Disconnect negative battery terminal to avoid possible fuel discharge if an accidental attempt is made to start the engine.
o   Loosen fuel filler cap to relieve tank vapor pressure.
o   The constant bleed feature relieves fuel pump system pressure when the engine is turned "OFF".
1.   Remove fuel pressure gauge.
2.   Reinstall fuel line.
3.   Connect negative battery terminal and START engine and check for fuel leaks.
4.   Install air cleaner assembly.
Specifications   


Ignition ON Engine OFF    62-90 kPa (9-13 psi)


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Re: GM TBI
« Reply #2 on: October 29, 2014, 06:18:49 PM »
A Basic Overview of the GM Throttle Body Injection (TBI) System
TBI Throttle Body Injection is a very versatile, highly adaptable form of electronic controlled mechanical fuel injection.  TBI provides the optimum mixture ratio of air and fuel at all stages of combustion.  TBI has immediate response characteristics to constantly changing conditions and allows the engine to run with the leanest possible air / fuel mixture ratio, greatly reducing exhaust gas emissions.   Because it's air / fuel mixture is so precise, based upon much more than simple engine vacuum and other mechanical metering means, TBI naturally enjoys an increase in fuel economy over a simple mechanical form of fuel introduction such as a outdated carburetor.
The TBI form of EFI is controlled by the ECM (Electronic Command Module) which controls the TBI based EFI system through all stages of operation according to data received regarding the current state of engine performance, speed, and load.  The main component of this system is the TBI throttle body injector, which is mounted on top of the intake manifold, much like a carburetor.  The throttle body injector is composed of two different parts; the throttle body itself, and the injector assembly.  Hard to understand, isn't it?   The throttle body is in fact, a large throttle valve, with a pair of linked butterfly hinged flapper valves, which are controlled by a simple mechanical linkage to the accelerator pedal.  Depressing the accelerator pedal will force the throttle valve to butterfly open further and further, increasing the flow of air through the throttle valve and instructing the ECM to add more fuel, thus producing more power, faster speed, and acceleration.
Attached to the body of the TBI unit are two sensors; the TPS throttle position sensor, and the IAC idle air control assembly.  The ECM uses the TPS to determine the accurate position of the throttle body valve, it's degree of cycling, and how open it is (0% to 100%).  The ECM takes readings from the IAC in order to maintain a constant idle speed during normal engine operation, during all stages of power, load, and combustion.
The fuel metering assembly contains a fuel pressure regulator which dampens the pulsations and turbulence generated from the very high pressure fuel pump.   Think of the FPR as a conditioner that smoothes out the flow of fuel from the outside to the inside of the fuel metering assembly.  The FPR also maintains a constant, steady pressure at the injector assembly.  Dual fuel injectors are mounted over the throttle valve, synchronized, and raised slightly over a venturi (narrowing radius) throat.  Each injector is controlled by the ECM through an electrically initiated solenoid (switch).  The precise amount of fuel delivered by each injector is varied by the amount of time that the solenoid holds the injector plunger open for operation.
A high pressure, high volume electric fuel pump is used with the TBI system.  This pump is located within the fuel tank itself (which can be a PITA if you have to replace it).  Once the ignition key is inserted into the ignition, and the ignition moved to the RUN or START position, the fuel pump relay instantly initiates the pump, beginning the transfer of fuel (via the pump) from the tank to the injectors.   A safety relay in the system shuts the pump off after two seconds, to keep the fuel from flooding.  Failure of the fuel pump relay will allow the fuel pump to operate only after four pounds of oil pressure have built up.  A high capacity fuel filter, similar to an in-line variety, is located on the left side of the vehicle, at the rear of the engine.
Two common mistakes when working with the EFI system.  The fuel system is pressurized.  If you remove a fuel line, you could/will get a face full of fuel!  The fuel pump used on the EFI system is much more powerful than that found on a carburetor installation.  For this very reason, the second problem is that you cannot use a EFI fuel pump to feed a carburetor, and you cannot use a normal carburetor mechanical style fuel pump (low pressure) to feed a EFI system.  In order to work on any part of the EFI system, you must first depressurize your fuel system!!!!!
The ECM found in General Motors' cars has the capability to 'learn' or modify it's programming with regard to differing fuel requirements over time. Don't get excited. This is not HAL from 2001: A Space Odyssey, and it's certainly not some super advanced neural net processor like the T800 Endoskeleton had in Terminator and T2. It's quite a bit simpler, but its a complex computer nonetheless, and it can adjust to different conditions easily. It learns, just like a human child, and that's the best way to put it.  It doesn't forget when you turn your car off either.  But, if you ever change your battery, or your battery goes dead for any reason, your computer will lose it's stored 'memory' and will have to relearn everything.  It's a quick learner, but it's something you don't really want to go through all the time.
The computer's instructions are contained on a PROM (Programmable Read Only Memory), which means that the computer can change it's operation according to pending needs. It then stores this new information, and how it should act, on the PROM chip. Since the PROM isn't volatile, it doesn't lose it's information when the battery power is cut off or the keys are taken out of the ignition.
But the computer takes a little while to adapt. So if you add a new cold air or ram air induction system and the car doesn't respond instantly, don't get depressed. The computer has just been handed a new parameter, it's working under new data and conditions, and it could take it a little while to figure out that the new cold / ram air isn't just a fluke, and that it should adjust to the new 'constant', but adjust it will. Be patient. The computer can make up for quite a bit of ham fistedness, but only to a limit.
And after that limit is exceeded? Well, you could always learn to program your own chips, and we may get to that later... But I don't think it will come down to getting that serious.
Why?
Well, most swapping and upgrading of the TBI system is pretty straight forward, and a lot of aftermarket companies make chips for these units. If you are going to get this technical into the game (I might, as some of you might as well), then you should think about getting a programmable EFI computer. Haltech makes an excellent model. Just plug it into your laptop and you can tune the engine with the engine still in the car!
Talk about high tech!  Does TBI sound like a bad fuel injection system now?  I didn't think so.  And we've cleared up some misunderstandings on how the whole system works.
____________________________
So, When Do I Need to Reprogram My TBI Computer Chip?
Ok, here I will outline some of the reasons that you will be required to either reprogram your own chip or if you don't want to spend the time and money, pay someone to do it... I will also highlight when you might be able to get away without reprogramming. In most worst case scenarios, you can just pay a hundred or so dollars and buy a aftermarket PROM chip geared toward performance. Companies like Hypertech make these 24 hours a day, so finding one won't be a problem.
Some Situations Where You Might Need To Reprogram Your PROM chip ....
•   Swapping the stock TBI system from or to an engine that differs in size by plus or minus more than 10-15% than the original unit. The TBI seems to not like much over 15% in size alteration for its new home (an amazingly adaptable system), so switching from a 305 to a 350 (or 355) should not be a problem. It really starts to struggle the closer you get to 30% over the original size of the donor motor. Switching the system to a 383 might present a problem, and require that you build up your TBI unit itself for the increased load. More on that later, patience, grasshopper. Learn to walk before you run. You can see that using a 305 TBI on a 350 won't be a problem, but your problems will start to increase the closer you get to 400cubes (about 30% over a 305cid). Putting a 305 TBI unit on a 454cid is going to present a whole range of problems besides the intake manifold (which won't fit) ....
 
•   So, when might you need to either reprogram your PROM chip or replace it with a high performance aftermarket PROM chip? Scrapping or not retaining *any* of the following systems: VSS, ESC, EGR, or the O2 sensor is a good way to almost instantly have to reprogram / replace your PROM chip.
 
•   If you increase your engine power output tremendously by the installation of superchargers, turbochargers, nitrous, more powerful cams, better heads, increasing the compression, etc. then you had better plan on upgrading your PROM chip. From the factory, it's not set up for race applications (no PROM chip is, so TPI guys can't rub your nose in this). GM never intended any ECM chip to handle race applications, that would get them in trouble with CARB and other Pollution Nazis. Your factory PROM chip is a brainwashed tree hugging hippy. Don't blame the chip. Blame the government. GM had to make your PROM chip with routines that would let your engine operate in conditions that would make the trees smile and the flowers happy. This probably doesn't make you smile or happy.
So, if your new TBI swap out is going to be intended for mild operations, like what you used your 305 for in the first place, fine. Keep the stock PROM. If, however, you are going to want to rip pavement, and you don't care about sad trees, crying hippies, or wilting flowers (none of which will really happen ...), then yank the PROM out and deprogram your ECM.
You'll find a rebel monster inside just waiting to be unchained.
 
Some Situations Where You Might Not Need To Reprogram ....
•   Keeping engine size as close as possible between the original and the new motor.
•   Retaining all of the original engine's sensor and control systems.
•   Taking a more conservative approach to modifications like exhaust and intake upgrades.
 
Situations Where You Don't Have To Do Anything To The TBI Unit Or System
•   Duplicating stock vehicle specs, weight, eng/tranny type, gearing from the donor vehicle to the host vehicle.
As you can see there are not many instances where retrofitting your TBI system from one engine to another will require reprogramming of the onboard ECM chip. The system is very adaptable. But you get further away (in size and in modifications) from the original operational parameters of the stock motor, the more the computer has to adapt. The more it has to adapt, the closer it gets to the point where it simply cannot adapt. If this limit is reached, and the computer cannot adapt any more, the ECM does the equivalent of a confused child in school. It raises it's hand and says "I don't understand what to do!" by turning on that annoying little "CHECK ENGINE" or "SERVICE ENGINE SOON" light.
Most people think that the CE or SES light is a bad thing. This isn't true. While it can indicate a possible malfunction (repair or replacement) of a component within the system, it can also be a way to talk to your computer. A primitive way, but a good way nonetheless. We'll get to that later.
Think of your CHECK ENGINE or SERVICE ENGINE SOON light not as an indicator of failure, no, instead think of it as a pager for your ECM. When someone wants to talk to you, they page you, don't they? Your pager on your belt vibrates or beeps or (if you are a total poser), plays some musical tune (like the first eleven notes of the Star Trek TV Series main theme...) that totally annoys everyone within listening distance. Well, think of the CE and SES light as the same thing as your pager, only no vibration (you hope no vibration!) and no music. The CE and the SES are simply the ECMs way of saying "Hey, got a second?   I need to talk to you!"  It can't play a musical tune, so it does the only thing it can to get your attention; it flashes the CE or SES light and keeps it lit until you answer it's page.
It could be important, it could be minor. But the important thing to understand and to remember is that your ECM is asking you for a few minutes of your time in order to talk over some really important stuff.  If you ever see your CE or SES light come on, I think you need to stop what you're doing and have a chat with your computer.  You do this with a scanner (you DO have a scanner, don't you?  If not, get a GM Code Scanner from any good parts house like Autozone, Pep Boys, etc.), which translates the computer's language into something you can understand.  The computer will talk to you in very short codes, called either error codes or trouble codes.   There is no speech involved, but the computer will 'flash', blink on and off, your CE or SES light.  A long flash is read as the 'tens' place, and a short flash is the 'ones' place.  So, if you are talking to your computer and the computer flashes the CE or SES light two long times followed by three short blinks, then that is Code 23.   Understand?  It's not that hard.  If you have a repair manual for your car (Haynes, Chilton, etc.) then you have a listing of error codes and what they mean.   I won't go into that here, it's just duplication.  Also, you can find the error codes on the Internet pretty easily.
So, the next time that your computer wants to talk to you, listen!   The computer is your friend and you don't ignore friends when they need to talk.  And make sure that your CE or SES light is working properly.  Remember, if the bulb is out, your ECM could be trying to talk to you, but you'll never know it!
___________________________________
Some notes on the GM Dual Injector TBI Unit ...
The system that I have on my L03 5.0 liter V8 was developed by GM for use on its pickups and minivans. Shocking. But that's because pickup trucks and minivans need lots of torque, and don't need highly specialized, narrow focus systems like tuned port fuel injection.  They need a fuel injection system that is easy to work on and adaptable to a wide range of conditions and operating parameters. Why do the most powerful trucks in the world, the Chevy and GM series of full size trucks, with their 270horse Vortec engines use TBI instead of TPI?  Easy. TBI is a lot simpler, it's got a wider range of operating parameters, and it's cheaper. TPI has Mr. Goodwrench cussing like a sailor. TBI has him smiling like a kid on Christmas morning.
It's so easy to work on, and that is what many people feel is the main reason that makes it a bad high performance EFI choice.  I mean, if you want high performance, then by the very nature of the definition of high performance, your EFI system has to be expensive, tricky to work on, hard to modify, and just an all around PITA to work on.  Right?
Wrong.  You can do things the easy way, or the hard way.  I'm not known for doing things the easy way, but choosing TBI isn't an easy choice.  It's the easiest EFI to work on, but it's also the hardest to get performance out of, just because no one else has done it before!  That means that myself and a few other brave souls are blazing new trails into uncharted territory, and we're doing it with nothing but our brains.
If TBI is so great, why didn't GM use it on other vehicles besides trucks and minivans?
They did.  TBI was used on GM's economy cars, the early Vortec series of popular truck engines (and later more powerful editions of the Vortec with TBI would run 250+ horse stock.  A 350 Vortec TBI engine could match a 350 TPI L98 engine easily, and make more torque!) and later on such engines as the L03 305, which found it's way into various 3rdGen F-bodies. People who badmouth TBI are generally owners of TPI. It is these same, sad individuals who forget that the Vortec series of Chevy trucks. TBI should not be seen as a step down from TPI, it should be seen as a step up from a carburetor, and as an alternative choice to TPI for high performance applications.   Don't think of TBI in a TPI or TBI situation.  If you have it, use it, don't lose it.
Think of the ECM as a spider, in a web. At each end point of the web is a sensor or other control device. When something causes a disturbance in the web, the 'vibration' or sensor reading is sent down the 'web' to the 'spider' (ECM) which reads the information and reacts accordingly.  Now, how TBI gets its input, well, that is supplied by various sensors located around the engine, in the engine bay, and around the vehicle itself.  Let's talk about some of those now...
Sensors, Inputs and Outputs Used
TPS - Throttle Position Sensor, the TPS measures the position of the throttle. Really complicated stuff there.  The position reading indication sent by the TPS to the ECM determines the amount of fuel to order the injectors to inject, and modifies the duty cycle of each injector as needed.  The degree of cycling of the throttle body valve is used to compute the duty cycle of each injector during high pressure fuel firing.
CTS - (Hey, a part of the engine with my initials!) Coolant Temperature Sensor, the CTS measures engine coolant temperature.
MAP - Manifold Absolute Pressure, the MAP sensor measures the amount of load that is on the engine by sensing the difference between the pressure in the intake manifold and atmospheric pressure. It compares what's going on inside (kinetic) with what is going on outside (ambient).  The MAP controls fuel mixture and timing.   The MAP measures vacuum in the manifold.
O2 Oxygen Sensor, the O2 sensor is mounted in your exhaust manifold or exhaust pipe. The 02 sensor measures the amount of oxygen in the exhaust stream. Too much oxygen indicates not enough fuel or a lean condition. Too little oxygen indicates too much fuel or a rich condition. The ECM then takes steps to correct this problem by adjusting the air / fuel (mixture) ratio.

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Re: GM TBI
« Reply #3 on: October 29, 2014, 06:19:17 PM »
Knock Sensor - the knock sensor senses detonation (which sounds like popcorn popping in a tin-can). Detonation can range from simply annoying to mechanically destructive. It should be avoided at all costs.   The ECM uses information from the knock sensor to adjust the timing in order to stop detonation.
ESC - Electronic Spark Control, the ESC module takes what the knock sensor detects and tells the ECM whether to retard ignition timing or not. Spark is advanced for high load conditions, and retarded (or cut back) for conditions of detonation.
The ECM also make use of other inputs to determine proper fuel requirements.  They are as follows:
•   Absolute Engine RPM is obtained from data received from the ignition module.
•   Battery Voltage is supplied to the ECM.
•   The ECM knows to increase idle RPM when the air conditioning is on through monitoring of the A/C Switch.
•   The ECM knows when the engine is trying to start and adjusts fuel accordingly thanks to communication with the crank switch.
The ECM controls the following items to maintain good power, mileage, idle and favorable emissions.
Fuel Injector - The ECM controls the amount of time that the injector is spraying fuel. This amount of time is called the 'duty cycle' of the injector. Within some parameters, it can be overdriven to increase performance, but too much is not a good thing. The faster an injector is forced to fire, the less efficient it becomes.
IACS- Idle Air Control Sensor, the IACS is an adjustable air leak into the engine.  It is a power valve which moves back and forth, constricting and enlarging, in order to adjust the air mixture. The ECM controls the leak to get a good idle. The readings from the IAC allow the ECM to adjust the motor's operations and idle accordingly.
MATS- Manifold Air Temp Sensor- Also the Manifold Absolute Temperature Sensor, provides input on manifold temperature and allows the ECM to adjust mixture accordingly.
Ignition Timing- the ECM controls the amount of timing advance or retard needed depending on engine RPM, power load and detonation detected. Timing will be advanced as needed to meet performance load parameters. It will be retarded, again as needed, to minimize or eliminate detonation.
Idle- The ECM also has control over the idle RPM, for example when the engine is cold it idles a little higher. Temperature readings to determine if an engine is cold or not are taken from the coolant temp sensor, and from the oxygen sensor. Once temperature reaches operating ranges, the ECM idles the engine back down.
Fuel Pump- The ECM also controls the fuel pump, turning it on before start, and keeping it on during cranking and run. Fuel pump pressure is also controlled by commands sent to the pump by the ECM. More load equals greater fuel pressure.
There are some other things that the ECM can control during normal vehicle operations:
VSS- The Vehicle Speed Sensor, which drives the speedometer readings and indicates true forward motion in speed of the vehicle.
TCC- Torque converter lockup controller. This unit works with VSS and locks up the torque converter once a 'cruise' range is selected. If the engine is in cruise mode, the TCC engages the lockup on the torque converter, and mileage is improved greatly.
EGR - Exhaust Gas Recirculation valve.  The EGR solenoid (if so equipped) controls vacuum to the EGR.
4th gear switch. Works with TCC to inform the ECM when the transmission and the engine have reached a cruise speed that will be maintained for some time.
Emissions Canister purge
Air injectors
Park/Neutral Safety Switch, should be used on all automatic transmission installations. This prevents the transmission from shifting from PARK or NEUTRAL to any reverse or forward range gear unless the brake pedal is depressed and held firmly. Kind of a way to keep idiots from hurting themselves, but it also keeps you from 'speed shifting' your auto from neutral to drive by 'slapping' it down.
 
The ECM has the following outputs to help us.  This is data that the ECM sends to the driver / operator as part of it's operation:
SES - Service Engine Soon, also known as the check engine light. It warns the operator of malfunctions with the system. When you see this light come on, grab your scanner and check the ALDL. Don't know what the ALDL is, no problem.
ALDL - Assembly Line Diagnostic Link. Where any GM dealer can plug their computer in and tell all kinds of stuff. This is where you will plug in your scanner (you do have a scanner, don't you?) and translate all those error codes into human talk that you can understand.  Depending on the year, make, and model, the ALDL is located in different places.  On the F-body, it is on the driver's side, under the dash.   Get a scanner at your local parts house (Autozone, PepBoys, DAPS, etc.).  It is worth it's weight in gold, and you can pick one up for about $20 or so.
Shift Light - There is also a shift light on the dash of vehicles equipped with a manual transmission. This light is designed to illuminate when set parameters are met for optimum gas mileage. This light is not functional on automatic cars (it has no purpose since the shifting chores are handled automatically).
 


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Re: GM TBI
« Reply #4 on: October 29, 2014, 06:20:49 PM »
1. Timing- There are 2 ways to do this.
a. disconnect the bypass wire and set timing to 0° at idle when warm. procedure- warm up motor then turn off. unplug bypass. Start motor. Set timing to 0°. Turn off motor. Reconnect bypass. Unplug ECM to clear fault code.
b. leave bypass connected and set timing to the value listed for your idle rpm and MAP setting at idle, based on your specific BCC-broadcast code. You can look up most BCC files here. Procedure-start motor and warm up. Set timing to the value listed in the spark table.

2. IAC reset/min idle speed- This sets the throttle plate on the throttle body to a specific rpm. I recommend about 500 rpm for most engines. Procedures- Go to sheet 7 of the pinout diagrams. At the top is the ALDL connector. You need to put a jumper between pins A and B of the connector. These are pins A9(wht/blk) and A12 (blk/wht) on the ECM. This puts the ECM into aldl mode. Turn the key on (not start) and the IAC should drive completely closed. You will normally hear a buzzing from the IAC. If you have the winaldl up and running on your laptop, you should see the IAC went from 145 to 0. Now unplug the IAC connector. turn the key off. Remove jumper. Start motor. If the idle is too low you may have to keep it running. On the front drivers side of the throttle body is the adjustment screw. It may be behind a silver plug. If so just use a nail or punch to poke it and remove it. Then use a #20 torx bit to adjust the idle speed to at least 100 rpm less then your warm idle speed. if 600 then set to 500 rpm. You are looking for the lowest consistant idle your motor will do. When set, turn off motor and reconnect the IAC. I try to keep the IAC count to at least 40 with the motor warm and idling.

3. TPS-throttle position sensor. With the idle set, you need to now set the TPS. This need to be set to about .54V. I normally shoot for about .6V.
The TPS is on the passengers side and will have 2 screws holding it on. The factory TPS will not have much room in the holes for adjustments so I use a drill bit or file to elongate the holes as needed. To adjust, just loosen the screws and trist the TPS. You can monitor the voltage on Pin B of the connector with the key on or at pin C13 of the ECM. You can also see it on the sensors tab of winaldl!! Anything away from .54V will also show as a percent of throttle. Such as .2 percent or 1.7 percent...depending on how far from .54 you are. I try to keep the idle setting to within 1 percent.
This is also a good time to check your TPS. Once it is set, just watch the voltage as you open the throttle. you should see a steady rise in voltage up to about 4.5-5V at WOT-wide open throttle. If it jumps up and down or skips some then you may want to replace it.

4. Fuel pressure- The system calculates the fuel needed based on the initial settings for injector size at a specific pressure. If the pressure changes then the fuel calculations will be off. I recommend checking the feed and return line pressures at the very beginning. This can save a lot of time later. The pressure is less then 15PSI so a simple cheap gauge is all that is needed. I picked up a HF fuel inj tester for $7 on sale. Comes with a T and a short rubber hose to install it.
The feed side pressure should be about 13psi and should not change with rpm or load. The return should be near 0psi.


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Re: GM TBI
« Reply #5 on: October 29, 2014, 07:20:22 PM »
1227747 ECM Wiring


A1- grn/wht- this wire is used to energize the fuel pump relay.
A2- not used
A3- not used
A4- gry- to EGR relay.(optional) This is a ground from the ECM to control the EGR relay.
A5- brn/wht- SES(service eng soon) light. This is a ground to turn on the light.
A6- pnk/blk- switched 12v from the ignition relay.
A7- not used
A8- orn- ALDL Serial data. This is your ALDL pin E data for your lap top.
A9- wht/blk- ALDL pin B diag mode. When jumpered to ground will set the ECM to ALDL diagnostic mode.
A10- brn- VSS speed sensor signal to the ECM (optional)
A11- ppl or blk- MAP sensor ground.
A12- blk/wht- System ground. Can be tied with D1. Goes to engine ground.

Just to clear the confusion on which pins are grounds I have taken a C3 ECM apart and labeled the pin locations on the plugs.
If you look you can see that D1 and D2 are solder connected and A11 and A12 are also connected.
So if either one of the two, example: D1 and A11 are grounded the other one will be. D2 and A12.


B1- orn- 12v fused from battery. I use an inline fuse on this. It also ties into C16.
B2- tan/wht- Fuel pump signal from the relay. This one ties into several places, the fuel pump, the relay, and the ecm. When the relay is on it sends 12v thru this wire to turn on the fuel pump, at the same time it tells the ECM the fuel pump is on.
B3- blk/red- EST reference.
B4- not used
B5- ppl/wht- EST high reference
B6- not used
B7- blk- ESC signal This is the knock sensor signal to the ECM. The knock sensor circuit is optional. If not used, tie this wire to C14 the 5v reference.
B8- dk grn- AC signal. This tells the ECM that the AC is turned on. This can be used to set the idle speed higher when you turn the AC on. I use it to increase the idle when using the compressor for on board air. Same thing!! Just tie it to the wire going to the AC clutch.
B9- not used
B10-orn/blk- Park/Neutral sw. This is optional but I have hooked it into the park sw on the tranny. It tells the ECM when you are in Pk or N. It can be used to give a slight adjustment to idle speed when switching from park to drive and back.
B11- not used
B12- not used

C1- not used
C2- not used
C3- IAC- Idle air control
C4- IAC
C5- IAC
C6- IAC -The ECM controls the IAC motor. It adjust the amount of air that is bypassed around the butterflies to adjust the idle speed.
Note: (For the IAC pins C5 and C6 are reversed on the 454 vs the SBC so swap those 2 pins if using a 454 TB with the bolt on IAC.)

C7- not used
C8- not used
C9- ppl/wht- Starter crank signal. Goes to the small terminal of the starter. The stock scout wire is white that goes there. Tells the ECM you are trying to start the engine.
C10- yel- Temp sender signal
C11- lt grn- Map sensor signal
C12- (1228746 only) IAT/MAT sensor
C13- dk blu- TPS sensor signal
C14- gry- 5v reference signal to map and TPS.
C15- grn- inj B ground signal. Most systems do not use this. It was used on some of the bigger engines to share the load of the injector signal.
C16- orn- fused 12v tied to B1

D1- blk/wht- System ground, ties to A12 and engine.
D2- blk- Sensor ground. To eng block or head.
D3- not used
D4- wht- EST control
D5- tan/blk- EST bypass. This is the wire that has a plug near the distr that you disconnect to set your timing.
D6- Tan- O2 ground to engine.
D7- ppl- O2 sensor signal
D8- D13 not used
D14- lt grn- Injector B ground signal
D15- blu- optional injector A ground signal
D16- blu- Injector A ground signal

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Re: GM TBI
« Reply #6 on: October 29, 2014, 07:25:25 PM »
Voltage Checks

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Re: GM TBI
« Reply #7 on: October 29, 2014, 07:30:05 PM »
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Re: GM TBI
« Reply #8 on: October 29, 2014, 07:31:17 PM »
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Re: GM TBI
« Reply #9 on: October 29, 2014, 07:38:42 PM »
1995 PCM Wiring

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Re: GM TBI
« Reply #10 on: October 29, 2014, 07:46:38 PM »
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Re: GM TBI
« Reply #11 on: October 29, 2014, 07:47:15 PM »
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Re: GM TBI
« Reply #12 on: October 29, 2014, 07:52:01 PM »
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Re: GM TBI
« Reply #13 on: October 29, 2014, 07:54:01 PM »
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