I have a 94 Z28. Starts easy, runs great for about 15 minutes or so. Then I feel a jerk in the steering, it runs rough for half a minute or so and then kills. Doesnt' matter if I'm driving fast or slow or even stopped. I pull over and it won't start for at least a half hour or sometimes longer. Then, it repeats the process. My handheld OBD2 scanner only works on 96 plus cars so I can't check it that way. Wondering if any of you guys have a clue as to what might cause this, never had this problem with any other car. HELP!

 

That's strange. Does the engine turn but not start, or does it just not turn at all? One guess would be something is heating up then starting to seize up. And if that's true it might be something on the accessory belt. You could try driving it until it cuts out, then pull the belt off and try turning everything on there by hand, water pump, alternator, power steering pump, ac compressor. If something feels really tight it might be the problem.

 

Here's your checklist,

Codes - Check for them first.

Fuel pressure - Should be 41 when priming the pump, about 38 at idle and around 43 give or take at full throttle. If its not within that, check out your fuel system.

ICM - Get a multi meter, pull off the connector to the ICM. Connect multimeter on DC setting to A and C as ground with key on. Should read 10+ volts. Repeat with D and C. Then switch to AC setting and connected B to C as ground and have a friend crank the motor. Should swing between 2 and 4 volts while cranking. Try when its cold and warm that will let you know if the ICM is getting signal. If it is getting signal your problem can be the ICM or the Coil. Try spacing the ICM away from the head as a cheap remedy.

Coil - Use the multimeter to check resistance of the coil. Stock coil should read around 8000 ohms resistance. Anything else replace the coil.

Opti - When you did the multimeter test on the ICM if it wasn't getting signal during the B terminal test then the ICM is not getting the signal to fire the coil. Check the wiring going from the Opti to the pcm and back to the ICM. If it checks out then the issue is more than likely the opti itself.

 

I'll check the belts when it does it again bluemaggot. If that's not it I'll run thru the diagnotstics justnasty. Wish my code reader would work on a 94! Thanks.

 

You need an OBD-I scanner for a 94. There are low $$$ used AutoXrays available on eBay, for example. You can get free scanning software if you have a laptop.... just need to make or buy a cable. What make/model is your OBD-II scanner? Some models are also OBD-I compatible, with add-on cables.

 

I have a UIFTECH U381 scanner. Pretty happy with it, bought it off ebay for like $80 if I remember right. Already paid for itself nailing a cyl 1 miss that just needed a new cable on another car I have.. I'm going to go to their website to see if they have an adapter for OBDI. I think I'm going to need to scan this first before I can figure this out. Thanks for you help.
Now I wish I would have bought a 96!

 

I bought an OBDI scanner, but no codes came up. No binding noted at belts. Fuel pressure good. ICM seems to read the reverse of what was recommended, 5 with key on, and 10 while cranking. What does that mean? Anyway, for some reason my z28 starts great when cold, sounds great. Gets warm, cooling fans come on, then a few minutes later, it kills and won't restart. I can't even trust it to leave the driveway anymore! I cannot figure it out, any help would be most appreciated. Thanks.

 

common bad opti symptom.had the same problem.

 

well I encountered the identical problem you have and I think I have fixed it (fingers crossed) with replacing the ICM and coil. I tested the coil with a multimeter and then tested the new one when I got it and they were identical. So pretty much all I have done is replace the ICM. So far I've driven it twice for over a hour and I can't make it duplicate the problem. I also did not have any codes and replaced the o2's some time ago and those are reading fine.

Hope this helps and good luck

-Brian

 

You didnt say if it turns over or not after it dies. If it does it could be any of the things that were quoted also could be ecm. The jerk in the steering is kind of odd. Did you try the scanner after the car dies, you may get a code while cranking. But like stated earlier start with the ICM then opti plus related wiring. Also may not be a bad idea to pull Alt. and have it tested.

 

When it dies, you have to check to see if you a losing fuel pressure, spark or just what. That is the only way you are going to narrow it down.

 

And how would he check the water pump? Its cam driven!

But i had a similar problem too...was the new MSD opti, sensor was heating up and breaking down but it could be other things too. Just throwing out a suggestion!

 

First of all, thanks for all the input and help I received so far. Well, I bought a new ICM, replaced it, fired right up and .......you guessed it........died after about 15-20 minutes of idling in my driveway. Hmmm.....must be a bad coil then? Replaced that, same result! So I guess it's not the coil nor ICM. It appears I'm getting no spark after it kills. The guy I bought it from said he just replaced the opti-spark system, so can that fail again after only a few thousand miles? I'm really at a loss here.

 

OH, by the way, it does turn over just won't pop.

 

Possible to go out if not installed right but still sounds iffy. Could be the crank sensor? This fixed the same issue I had with the 15 min stalling and no start but cranking before this recent issue with the ICM. I replaced the crank sensor again before the ICM this time and it didn't fix the problem. Be more than happy to send you the old sensor (probably still just fine since it didn't fix my problem) to throw it in your car and see if it fixes it. Hate seeing people throw money at a car like I did but got lucky.

-Brian