Here we go again. My 1991 L-98 has done it again. I'm driving along an all of a sudden the engine cut out, I get it to start and pull into a parking lot where it continues to cut out. It starts right up but will not stay running. I wait a few minutes, get it to start and make it home crawling. This has been going on for a while. The car runs great for a month or more, and bang it happes again. I have driven the car home, let it sit over night and the next day starts right up and has no problem. It makes the car unrelieble. I have taken it to two different Chevrolet dealers and always get a good bill of health. I have checked or replaced the followng with no luck. New distributor, wires, spark plugs, EGR valve, fuel filter, PCV valve, air filter. Right after it's done it, I have checked the fuel pressure as well as sparks, and everything seems fine. I just ordered new oil pressure sending sensor as well as a idle control sensor. I have read several postings on similar problems and have tried all recommendations. Don't know what else to do and I am now thinking of buying a new ECM. I'm pretty sure it has got to be a sensor going bad, but can't figure it out. I just had the car tuned two days ago at a Chevy dealer and they even told me the car is in perfect condition. No lights on the dash or codes. Any one been able to correct this problem???

 

They don't stop for no reason, the problem is finding the reason. All engines require spark and spark at the right time, fuel, air, and in the correct ratio. Keep some tools with you and when it stops, check for spark with a timing light, check for fuel pressure, pull an injector plug and use a noid light or a low power 12v lamp across the injector plug and determine if the injector is being pulsed when cranked.

 

I assume you are getting no stored trouble codes.

Check all ground connections on the engine.

If you had a logging scan tool you could continuously monitor the ALDL to see if anything shows up when she misbehaves.

Frankly it sounds like an electrical problem. If you don't find a loose ground or bared wire I would start thinking about the ECM. You might open it up and reseat the CalPac and giggle the two connectors to assure they are seated properly.

 

Sounds very similar to what my '90 has been doing... Runs good when its cold, no trouble codes, cuts out and dies for no reason, sometimes it starts up again and sometimes it doesn't until I let it sit and cool for a while. I just ordered a new distributor control module for it because mine is bad. You might look into the control module/pick-up coil to see if thats the problem. Hope this helps.

 

Autozone 25 bucks

 

Does it cut out when your coasting to a light? Mine did this, and only once in a while. It ended up being the idle air control valve. This unit in the throttle body controls the idle speed, and if it goes out, the engine will stall when you let off of the throttle. It won't idle, but will run if you keep your foot on the gas. Cleaning with out with carb cleaner helped a bunch, but I ended up having to replace it later.

Another possible candidate you haven't tried. There is also a weak part in the distributor. One of the connection things, I think it's called the terminal block, goes bad, and it will kill the car all together. Usually this goes all at once, but I've heard of one that went intermittently before going out all together. They thought it was bad gas, but ended up being this.