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1996 Corvette changed coil and controller. now won't start

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Old 05-13-2018, 11:15 PM   #1  
Southern Boy
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Default 1996 Corvette changed coil and controller. now won't start

My 1996 was idling rough, but at least it was running. I changed the coil and ignition controller and now it turns over well, but will not start. I put the old coil back in and still will not start. Any ideas would be greatly appreciated.
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Old 05-14-2018, 08:03 AM   #2  
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Codes? Do you have service manuals? Spark, injector pulse, fuel pressure?
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Old 05-14-2018, 08:50 AM   #3  
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You mention coil and 'controller' - I'll assume 'controller' is module. Correct?

When it didn't run you mention only replacing the coil. You left the new 'controller/module' in place?

Brand and part #'s of what you bought? Where did you buy? If 'controller' is actually the module and you've not busted any electrical connections maybe you exchange the module.

Coil wire connection?

You replaced 1st 1 & 5 but 2nd time only put old #5 back to the car?

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Old 05-14-2018, 09:40 AM   #4  
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In addition to the advice above, it's worth noting that new replacement ICMs aren't always good. I replaced mine once with a brand new one that was DOA.
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Old 05-14-2018, 03:52 PM   #5  
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Do you have fuel pressure? Test and report back.
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Old 05-14-2018, 06:06 PM   #6  
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..... Also check the electrical connectors for damaged or displaced pins ... the plastic is old and subject to engine heat and will get brittle .....
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Old 05-14-2018, 11:15 PM   #7  
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..... Also check the electrical connectors for damaged or displaced pins ... the plastic is old and subject to engine heat and will get brittle .....
Thank you all for your replies. Just to clarify, I replaced both the coil and the module at the same time. The 1996 C4 (LT1 engine) had been starting reliably but idled rough and was a little ornery restarting once it was warmed up - but it did start after a little cranking. At highway speed it ran well. Once I replaced the coil and the module it refused to start. I replaced the new coil with the original coil and it still refused to start. It seems to be getting fuel as it smells of gasoline after trying to start it. It's a little hard to test the spark as I am a farmer and the nearest neighbor is a few miles away and most are busy like me with spring planting. The pins in the electrical connectors all seem good, but I did notice that the coil electrical connector only seems to have two wires going to it and yet it has three pins. I do have both a Chilton and a Haynes manual for the car, but I find them about as useful on this problem as teats on a bull. Logic says the next step is to put the original module back in the car and see if it starts unless you all have a better idea. Again, I really appreciate your suggestions and follow-up with my questions.
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Old 05-14-2018, 11:59 PM   #8  
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Thank you all for your replies. Just to clarify, I replaced both the coil and the module at the same time. The 1996 C4 (LT1 engine) had been starting reliably but idled rough and was a little ornery restarting once it was warmed up - but it did start after a little cranking. At highway speed it ran well. Once I replaced the coil and the module it refused to start. I replaced the new coil with the original coil and it still refused to start. It seems to be getting fuel as it smells of gasoline after trying to start it. It's a little hard to test the spark as I am a farmer and the nearest neighbor is a few miles away and most are busy like me with spring planting. The pins in the electrical connectors all seem good, but I did notice that the coil electrical connector only seems to have two wires going to it and yet it has three pins. I do have both a Chilton and a Haynes manual for the car, but I find them about as useful on this problem as teats on a bull. Logic says the next step is to put the original module back in the car and see if it starts unless you all have a better idea. Again, I really appreciate your suggestions and follow-up with my questions.
Another question if I could. Being a farmer and usually working on farm equipment where more grease is better, I slathered on the dielectric grease quite thick - on both sides of all the plates behind the module and even in the coil to opti plug. Could this be causing a problem? Maybe I should have stuck to tractors - you can work on them standing up and not have most of your skin on your hands peeled off.
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Old 05-15-2018, 07:36 AM   #9  
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Farmer = DIYer on everything. EBay will have factory service manuals. You need a basic obd2 scanner, spark tester, noid light, and fuel pressure gauge. The spark tester and a good old plug wire will ease atleast checking spark from coil.
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Old 05-15-2018, 09:33 AM   #10  
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Quote:
Originally Posted by Southern Boy View Post
Thank you all for your replies. Just to clarify, I replaced both the coil and the module at the same time. The 1996 C4 (LT1 engine) had been starting reliably but idled rough and was a little ornery restarting once it was warmed up - but it did start after a little cranking. At highway speed it ran well. Once I replaced the coil and the module it refused to start. I replaced the new coil with the original coil and it still refused to start. It seems to be getting fuel as it smells of gasoline after trying to start it. It's a little hard to test the spark as I am a farmer and the nearest neighbor is a few miles away and most are busy like me with spring planting. The pins in the electrical connectors all seem good, but I did notice that the coil electrical connector only seems to have two wires going to it and yet it has three pins. I do have both a Chilton and a Haynes manual for the car, but I find them about as useful on this problem as teats on a bull. Logic says the next step is to put the original module back in the car and see if it starts unless you all have a better idea. Again, I really appreciate your suggestions and follow-up with my questions.
Testing spark is easy, pull #4 or #6 plug (these seem the easiest to get at for me anyway). Reattach spark plug wire and run a jumper wire from the plug to an engine ground. Set the plug on top of the intake so you can see it from the front seat with the hood open. Turn the lights down low and crank it over. If it's got spark you'll see it.
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Old 05-15-2018, 09:58 AM   #11  
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I do have a obd2 scanner and it is not indicating any codes. The idea of how to test spark from pocoW is great and much appreciated. I will give that a shot this evening. I also may have created a problem by slathering dielectric grease all over the 3 plates that are behind the module. I even put some in the plug wire for the coil (to the opti). Is a bunch of dielectric grease too much? With farm equipment grease is your friend, maybe not so much for corvettes. I don't know if clear contact between the module plates and the block is needed for a ground.
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Old 05-15-2018, 11:55 AM   #12  
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You don't want dielectric grease there, you want thermal paste which conducts heat from the ICM.
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Old 05-15-2018, 12:06 PM   #13  
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Quote:
Originally Posted by Southern Boy View Post
I did notice that the coil electrical connector only seems to have two wires going to it and yet it has three pins.
This (I'm quite sure) is of no concern to you. The coil is used on all of the Vortec OBD2 variety also and the 3d terminal is TACH out, on your Corvette tach is actually a PCM function.

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Old 05-15-2018, 12:32 PM   #14  
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You don't want dielectric grease there, you want thermal paste which conducts heat from the ICM.
That's correct. However, I doubt that would cause it to fail to even try to start. I could see it causing the ICM to overheat and shut down the car after a minute or so, but when everything is cold it should at least start and run for a bit.
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Old 05-15-2018, 03:53 PM   #15  
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That's correct. However, I doubt that would cause it to fail to even try to start. I could see it causing the ICM to overheat and shut down the car after a minute or so, but when everything is cold it should at least start and run for a bit.
Thank you MatthewMiller. I was afraid my heavy use of dielectric grease could have shorted something out - particularly the coil to optic plug
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Old 05-15-2018, 10:26 PM   #16  
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Quote:
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Thank you MatthewMiller. I was afraid my heavy use of dielectric grease could have shorted something out - particularly the coil to optic plug
I doubt it, but it would be worth cleaning the metal terminal on that plug just to make sure. I think the grease there should be on the boot but not the actual electrical contacts.
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Old 05-15-2018, 10:44 PM   #17  
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There are also 2 pin outs of ICM. The switch was around 94ish, and they will not worth with each other. You may have an early pin out ICM.
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Old 05-16-2018, 03:48 PM   #18  
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There are also 2 pin outs of ICM. The switch was around 94ish, and they will not worth with each other. You may have an early pin out ICM.
I put the old ICM back in with the old coil and still no joy. Really confused now as it ran prior to changing out ICM and coil so I would think having have the old coil and ICM back would result in it starting. Getting close to digging a hole and burying it in the back pasture.
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Old 05-16-2018, 07:01 PM   #19  
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Thanks to an idea here, I was able to put a spark tester on where I could see it while cranking over the engine. No spark! what could I have done by changing the coil and ICM? The original ICM and coil are back on the car so it isn't a matter of defective new parts.
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Old 05-16-2018, 09:23 PM   #20  
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You need to follow shbox lt1 no start guide.

From memory, to get spark the icm needs a signal from the ecm to send the trigger to the coil. Then the coil woll fore, and send spark thru the opti. So I would check if you'e getting signal to the icm, and then from the icm to the coil.

It's an old car, you may have broken a wore during the install.
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