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Discussion Starter #1
Hi all,
I could use some serious help as I am about to give up and I am out of money. I have a 1996 Trans Am with an LT1. I was driving home on new years eve and my car died. I got it home and started to check for the three basics. I just bought this car and had the plugs and the wires ready in the garage to replace them so I did it while it was down. The plugs where so bad that i decided after changing them I would try to start the car. I fired up the car that night and she ran much better on start up but i noticed lots of white smoke coming from my exhaust that smelled rich. The morning of new years day I took the car up to the gas station 5 miles from my house and she was running great. After I got gas she stalled out as i was pulling out into the street. I pushed her back into the parking lot let her sit over night and she fired back up so i drove her to the house and into the garage again to start diags. I hooked a fuel pressure gauge up to the rail to test fuel first. I was dropping pressure as soon as the key was turned to start the engine or as soon as it was turned off. From simple checks I figured out the check valve for the return side was at fault and replaced my fuel pump. After fuel pump replacement she does not drop pressure at all and stays around 38. I took the car around the neighborhood and she drove beautifully with no more rich smelling exhaust to speak of. Then stalled at right about 5 miles or 10 minutes of driving half a mile from the house. this time she was kicking and sputtering like she didn't want to give in to shutting down. Once again got her home waited 24 hours and she fired right up and I pulled her into the garage. This time I did not have to wait 24 hours she will fire right up but die 1 minute later but as like she does not want to give in. She restarts only after a few minutes of relief. Once again I hooked the fuel gauge up and pressure stays around 38. I did the wait test and after 5 minutes it drops to 25 and ten minutes it drops to zero but does not lose pressure with the key on and engine running. I am at a loss here and cant figure this out. Please someone give me thoughts on what is going on or a direction to take or something I am forgetting. Thanks

Parts Changed/ tested-
Optispark- October 20
Ignition coil- October 20
ICM- October 20
MAF- Test good January 21
Plugs wires- January 21
Fuel pump- January 21

Global Moderator
13,339 Posts
Welcome to the forum.

Did you put heat sink compound on back of icm and on it's heat sink? This is the same stuff that's used on computer processor chips. Without the heat sink compound, the icm will either burn out or develop running problems when it gets hot.

Take the icm to an auto parts store. Have them run many test cycles to get it good & hot. That's when icm likes to fail.

Have you hooked an obd 2 scanner to car & checked for codes. There are several opti & icm codes that don't light the ses. If you bought any opti besides GM, Delco, or Delphi, it could be already failing. Only 100% way of testing opti low & high resolution signals is with an oscilloscope.

You can buy a PC based scope on Ebay, Amazon, etc for around $70 Use it to check opti low & high res signals. They should be a well defined square wave. See if wave changes shape or disappears when car starts acting up. You might also want to tape the gauge of your fuel pressure tester, to your windshield. See if pressure falls down when engine starts to die.

Herr's a link to the 96 factory service manual. It has code explanations, testing, & complete wiring diagrams.

An opti wiring pigtail could be causing your problem. On a 25 year old car, it has a good chance of being bad. It won't break the bank to buy a new one.
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