Hi all,
well.... this is a weird one. The 90 c4 will run like a scalded ape one time, the next it runs like it is starving for fuel. I had to have it towed home yesterday; it left me dead in the store parking lot. Today it started right up and runs fine, smooth as silk. Turn it off for 1/2 hour or so and it will start up, but runs like 4 of the plug wires are pulled. You can't touch the gas at all or it will die. It will idle but very badly. Turn it off and wait a day and it runs fine again.

I have replaced the plugs, wires, cap, rotor, fuel filter, oil, oil filter, air cleaner (k&n), idle teensier, serp. Belt, and filled it with 91 gas with a bottle of 7 point oct. booster. Fuel inj. cleaner, short of removing the radiator cap and driving a new Vette under it, I’m at a loss to know what's going on here. Anybody ever have this happen to them before, or is my Vette gone mad?

Could the computer be going **** up? It was scanned and didn't throw any codes. Someone told me the ign. module might be going bad. Would it run one time and not the other with that going out? When it is acting up it will start up and die off. After a while it will start up and idle poorly, but die off if you even think of touching the gas. This car has always ran very good, it is in great shape and well taken care of.

Any help would be great,
Gregg

 

Check to see if the ECM was upgraded via recall. Local dealer should be able to tell from the VIN. My 90 acted similar right after I got it around '93... wouldn't idle, & basically ran like crap. Dealer kept playing around & then after about the 5th time in (no charge each time as I had bought it from them recently) they thought to check & there had been an upgrade. No similar problems since. Though now that I have a factory manual I wouldn't dream of taking in to them for anything. They don't even have a manual for it if you can believe that...

 

I recently had a simular symptom. THe damn thing would run fine and quit if I was running uphill. Let 'er cool for a few minutes and all was well. Ended up the ignition completely failing making it easy to fix. The HEI was the problem. I'll be carrying a spare one from now on.

-JRC-

 

tough to say, sounds electrical. intermittent electrical problems are the toughest... but here is something you might try to rule out the EGR valve:

symptoms sound like the EGR might be sticking open after a drive... If it is open @ idle your car will barely run.
Something to try, remove and plug the vacuum hose to the EGR. When the car heats up to normal you'll get an error code.. (EGR not open) but ignore it for now. If your bad runnib=g symptoms disappear then you've found it.

 

Wait a minute.....I thought this was the description for the fuel pump going bad? My '90 does the same thing, get on it a little, going uphill and it will die and then catch and accellerate. Does yours completely die and stall? Or just stumble?

 

Your problem sounds like you need to put gas in your tank.
I think most of us have your problem when our gauges show 1-3 bars.

 

I would HOPE he's tested beyond this, but...

Intermittant electrical problems can be a bear to track down. I'd get the easy stuff out of the way, first. When you disconnect and plug the vacuum to the EGR, make sure it is at a time the engine is idling properly. You don't want to disable it while it is stuck open.

My favorite is a failing fuel pump. Attach a pressure gauge where you can read it, like taped to the windshield. Keep a close eye on it, especially when you're having problems.

If it isn't the EGR or fuel, you have a difficult elecrical trouble shooting job ahead of you.

RACE ON!!!

 

Mine does it with almost half a tank.

New fuel pump for me.

 

So heres the deal, buy the HEI from Kragen or AutoZone. Less that 30 bucks! What the heck, if it doesn't fix your problem, keep it as a spare part.

BTW, I first measured fuel pressure to ensure the pump was not a problem. Then used a timing light and soldering gun to identify the missing "spark".

-JRC-

 

Had the same deal...would drive up to the store go in and when I came out it would start...idle really rough...no acceleration...would go a block and die...and then wouldn't restart for a couple of hours.

Here is what to do...if you can hook a fuel gage to the test port on the rail and tape it to the windshield so you can see it (yes it will be stylin').

What you should see is when you turn the key, the pump will run for 2 seconds and should pressure the system to say 36-42lbs. If it only makes 20-24lbs....it most likely will start but will run BAD (limp homw mode). When you accelerate the pressure should at least hold if not go up slightly.....if it goes down when you accelerate....that's bad too.

Mine did both of these....put in a new fuel pump and all was right with the world again...

good luck!