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Discussion Starter #1
Ok let me start out by saying the car runs perfect until it gets warmed up then it will die and not start up right away, if you let it sit awhile it starts up fine and has no issues until it gets warm again. I replaced the ICM thinking that it was getting warm and then having issues. It has good fuel pressure and good spark when its cold I have yet to test anything wants its hot. Opti was changed about 3-4k ago but im leaning away from it because it runs so dang good until it dies. Could it maybe be the coil causing this issue? any help would be great.
 

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lots of electrical things can fail when they heat up and then work when it cools down. on these cars though, opti and icm are the really common ones..

can a coil fail in a way that would fix itself after it cools off? yep. a crack in a winding can be small enough not to matter, then when the windings expand... lose contact.

can an opti die when it heats up, then work again when it cools off (kind of like an ICM)? yep! in fact it's fairly common, especially with 'off brand' optis.

is it setting any codes? have you scanned it?

past that, you need to figure out when it dies, if you lose spark, fuel, or both.

if you lose spark only, you're looking at the coil, icm, or high voltage side of the opti..

if you lose fuel only, on ALL cylinders, you're talking fuel pump.

if you lose spark AND fuel, it's pretty much just the opti or the wiring for the opti.
 

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ok I replaced the ICM yesterday no effect, today I replaced the Coil again no effect! I also scanned the car it has no codes, will it only pop a code when it has a issue? I had the scanner hooked up and turned the car on and let it run for about 10 minutes while I watched the scanner then turned the car off and tried to refire the car and all it did like always was just crank and crank. I then let the car sit for about 15 minutes and it fired right up. I had to stop for the day to head to work so tomorrow im leaning towards maybe a fuel pump, filter or maybe even a relay issue. So first thing ill check is the fuel pressure and go from there. Im kinda new to the LT1 cars so may take me sometime to learn everything. Thanks for your help so far.
 

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ok I had a chance to work on the car this weekend, here is what I had happen this time. Car was never moved or taken out of park so with that I had a fuel gauge hooked up turned key to on and pressure came up to 40 lbs until I started the car it dropped to around 37 to 38 lbs and would go up alittle as I revved it up, car ran fine with no issues or lights. I ran it up to around 180 degrees the turned it off and tried to restart which it did with NO issues so I keeped it running and would turn it off and on until I hit 220 degrees at this time I noticed the fans where not turning on and I turned it off and restarted about 8 times with 2 of the times the car started but sounded like it was running on 4 cyl was really weird and the fuel pressure didn't move around at all during these 2 times but I never could get the car to not start. So now im really stuck and don't know where to go from here. Anybody have any Ideas? could the starting issue and dyeing when hot have anything to do with me not working the Transmission and causing a load on the ICM and coil?
 

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shoebox kinda typoed there.

you need to check if you're missing spark or fuel, not necessarily spark or fuel *pressure*

you need to make it fail, then check for injector pulse and spark.

its good to confirm fuel pressure, but just because you have fuel pressure doesnt mean the injectors are firing.
 

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shoebox kinda typoed there.

you need to check if you're missing spark or fuel, not necessarily spark or fuel *pressure*

you need to make it fail, then check for injector pulse and spark.

its good to confirm fuel pressure, but just because you have fuel pressure doesnt mean the injectors are firing.
True, but you will go no fuel delivery without pressure and it is easy to check running with a gauge. Most of the time, if there is pressure, there will be fuel delivery. There can be trouble codes for some injector problems, but none if injectors are clogged (but intermittently clogged would not be so likely).
 

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Discussion Starter #9
ok well tomorrow if the rain holds off ill drive it into work and see if I can get it to have issues again! Thanks for the info on the cooling fans that's good to know that they don't come on as early as I figured they would so ill keep everybody posted once I figure it out. Also the temps here in Indy have been low and I did have the hood up while testing so maybe that had alittle to do with things not heating up like before.
 

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Next thing to check, make sure your intermittent problem isn't the electrical part of the ignition switch. It's located under the dash attached to steering column.

Check it for obvious things like burn marks on the connectors, burnt pins, bent pins, pins making poor contact.

Then get a wiring diagram for the ignition switch. What you need to do is test the 12 volt inputs to the switch and the 12 volt outputs from the switch. Use a multimeter set to DC volts. Use the wiring diagram to find all input and output wires.

Do a baseline check when car is running well. Then when problem occurs, check the outputs first to see if any of them have failed. If so, then check inputs to see if any of those have failed.

If only a output has failed, when you have your problem, then it's likely the electrical part of ignition switch is bad.

One more thing to check when car dies. Do you have 12 volts at the coil power wire and icm power wire. If your car is an automatic trans car, the trans gets it's power from the same fuse as coil & icm. If there is a problem in the trans circuit, it can pull power down in the coil & icm part of the circuit.
 

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Discussion Starter #11
Yes the car is a automatic so if im having issue because of that how would I go about fixing that? would it be a fuse issue or maybe something shorting out in the wiring for the transmission? But yes ill check the ignition wires also thanks for your help with this I really would like to get back to not having to wonder if the car is going to make it to point a or b or not.
 

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First thing you will need are wiring diagrams. 4th gen section has 96 factory service manual. Should cover your 97 as well. Look for thread titled "GM service manuals"

When looking at wiring diagrams, you will note that trans gets power from same fuse as coil & icm. Do a visual check of trans connector, basically looking for same conditions as ign sw connector. However, the trans check gets more involved if you don't find a fault with connector or wiring to trans connector.

If all is well there, the easiest way to see if solenoids and switches are working correctly is to hook to an obd2 scanner that does real time sensor scans and check the trans data while driving. If there is anything amiss with the electrics, the scan readings should point them out. You might even throw a trans code or 2. Don't know if they light the ses or not, but service manual would give you that info.
 

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Discussion Starter #13
Just wanted to let everybody know that I am still working on this issue, I drove the car again to work tonight about 20 miles one way and have had no issues with the car and also left to go get dinner about 5 hours into my shift and also had no issues when I restarted the car and returned to work. So as of now its just a sit and wait for the car to either have no issues or for it to not start so I can trouble shoot it. Ill keep progress posted as I go!! Thanks again
 

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Discussion Starter #14
Ok I finally drove the car ALOT today to try my hardest to get it to do something and it finally died on me as I was coming to work, I was testing the coil and ICM and the fuel pressure everything was checking out ok so I tried to start it up and it started so I hurried the rest of the way to work and it finally threw a code PO400 Exhaust Gas Recirculation Flow so would this alone cause the car to die and not wanna restart right away? Ill keep digging to see if I can figure it out but that's what I have so far. Thanks
 

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If your egr valve is stuck open and allowing exhaust gas to recirculate at the wrong time, yes it can cause car to die. I would imagine that starting it back up would be difficult also because of the diluted mixture trying to burn.
 

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NO, don't go spend money. Test first, my theory could be wrong.

Download the 96 service manual in the 4th gen section and do the tests listed under PO400. Then if it's the egr valve, get a new one. Look for thread titled "GM service manuals".
 

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Discussion Starter #18
Will do im at work so ill have time in a few to test it and hopefully its my issue because im about to pull my hair out trying to find my problem.
 

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cocobolo95 I was going to test my EGR but I need some tools that I don't have and it will be money well spent just to buy the EGR and swap it out and if that's not the issue ill atleast have a spare on the shelf. But what I noticed after it cooled down for about 10 minutes when I finally got it to start it was spark knocking for a few seconds or atleast ticking, but after just a couple seconds it went away and ran fine until I got to work. Then I let it sit all night and put the fuel pressure gauge back on it to check to see if that was still getting good pressure which it was but I noticed when I went to leave work that the gauge had fell from 40 Psi to 0 without me relieving the pressure from the gauge. Should the gauge hold the pressure or will it bleed off over a few hours? Just trying to give all the info that im getting so someone might have a idea. Im ruling out a fuel issue because the gauge never dropped below 35 psi even when it died on me. BTW its only died on me twice and both times is when im coming to a stop and after the car has gotten really warmed up atleast 20 miles driving before it dies on me, but let it set a few minutes and it starts back up and runs fine for atleast 8-10 miles before I shut it off.
 

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8 hours at work is long enough for pressure to bleed back down to 0.

Did you run the tests I listed in post #10? When your car dies you need to check for spark with a spark tester that puts a load on ignition system that simulates compression. Sold at most parts stores.

Use a spark tester because many times a spark will jump in free air but fail under the pressure in the cylinder.

Have you looked at the electrical part of the ignition switch, located under the dash attached to steering column. It could have loose or burned pins that lose contact when they get hot.

Since there are several outputs of battery power on ignition switch, you could lose power to ignition and still have power to other things.

So study ignition wiring diagram, and when car dies, check to see that coil and icm are getting power with key in on position.
 
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