Another LT1 No Start!
Thread Starter
Teching In
Joined: Jun 2015
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Another LT1 No Start! Ok guys kind of a long story here. So I know there is a ton of information on LT1 no start issues but my issue seems to be different in nature. The car is a 93 Trans Am I went to change the famous oil leaking intake gasket today and the job went smoothly. Got everything all hooked up and sure enough it won't start. The car ran perfect before I took the intake off. I started looking into it and theres no spark. I of course assumed the opti spark but I checked for injector pulse with a noid light and I do in fact have injector pulse. It will pulse each side of the engine 3 times then stop. I assume they stop pulsing because the computer knows the engine didn't start and is preventing it from getting flooded. If what I have read is correct if the injectors pulse I have a low res. signal from the opt to the ecu. That basically eliminates the opti but I went through the motions and check from ground both 5v reference and the 12volt power. everything checked out. I then checked for power and ground at the icm that all checks out. I checked for ecu signal at the icm using the multi-meter looking for 1-4 ac volts. During crank I got 1.3 volts at the icm. that means the ecu is sending a pulse to fire the coil. I then checked for the same 1-4 volts ac at the coil and there is no voltage there. I figured well it must be the ICM turns out they are $130 and so I took it and had it tested at the parts store. They tested it 3 times and it checked out good each time. I guess which brings me to the question of do I just get a new icm and not believe the bench test and take the chance of it not solving the problem or could there be another issue to look into first. The crazy thing is how can something I never touched go bad sitting there. Any ideas/ suggestions? Thanks
TECH Enthusiast
Joined: Jan 2013
Posts: 686
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From: Thibodaux LA
id check your fuses. a wire may have shorted out or grounding out some where. i happened to me when i did a trans swap. long story short it was the ignition fuse. have fuel. wasnt getting spark. get a new icm, if it still doesnt work you can return it
I don't know if you fixed it or not but I would check fuses and then if they check out OK I would then take the plug wire off the coil and put a screw driver up to it and see if that has spark if it don't then it's either coil or icm but if it does have spark then it could be cap and rotor on the opti. Also to save you money I would go to the junk yard and grab a couple icm and try them any lt1 car or Chevy blazer will work they use the same ones
Thread Starter
Teching In
Joined: Jun 2015
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got it going! Sorry guys a little late here but I hate leaving threads without a solution. Turns out the pigtail on the ICM was bad. I back probed all of the wires coming out of the ICM but I still didn't get a output signal for the coil so naturally I assumed it was the module. anyhow its up and running! Thanks guys!
