94 Corvette Problems
Thread Starter
Heel & Toe
Joined: Apr 2022
Posts: 18
Likes: 24
From: Monticello, Iowa
94 Corvette Problems
Bought my first c4. 94 with 50k. Had it for a month and it has been an absolute nightmare. Runs perfectly until it warms up and then will stall like the key has been shut off. Usually about 3-5 miles of driving or 10 min of idling. I Have been towed home twice now and that was enough. Dealer said “we put in a new fuel pump”, but unsure. I have put in a new ICM and battery so far. I believe it sat quite a bit the last 7 years.
Thread Starter
Heel & Toe
Joined: Apr 2022
Posts: 18
Likes: 24
From: Monticello, Iowa
More info
It will occasionally run for longer but tonight I took my daughter out for a ride and I dropped the hammer from a dead stop and it took off to about 3500rpm and died. Had to pull it home again. I budgeted 5k to fix/restore and just want to be able to go for a reliable drive. I am taking it in to a gm tech next week. I assume either fuel or opti.
Thread Starter
Heel & Toe
Joined: Apr 2022
Posts: 18
Likes: 24
From: Monticello, Iowa
I’m done working on it until I can get it scanned. I am not limber enough to get under to bridge the 4/12 pin to get the codes. it does flash “sys” every 15 sec while running. I am not a mechanic, but I bought the fsm books. Hopefully my mechanic can make short work of it. It runs so good when it does. Very odd to me.
Instructor
Joined: Apr 2022
Posts: 142
Likes: 48
From: Central NY State
Following what you find out.
I have a '93 that I just got and it is doing the same thing. I haven't had time to start diagnosing myself, but plan on starting that soon. After I put a new battery in and see if any codes pull on the jump method, I'm going to try a bag of ice on my ECM and see if it stays running once its up to temp, as the solder joints are known to go bad in them at least on early 90s.
Keep us posted what you find out.
I have a '93 that I just got and it is doing the same thing. I haven't had time to start diagnosing myself, but plan on starting that soon. After I put a new battery in and see if any codes pull on the jump method, I'm going to try a bag of ice on my ECM and see if it stays running once its up to temp, as the solder joints are known to go bad in them at least on early 90s.
Keep us posted what you find out.
Thread Starter
Heel & Toe
Joined: Apr 2022
Posts: 18
Likes: 24
From: Monticello, Iowa
We discovered gas in the oil today so they are going to put in new injectors/fuel pressure regulator. I am unsure of that would cause it to stall but everything else seems good. It only dies when warmed up.
Advanced
Joined: Nov 2008
Posts: 92
Likes: 46
Impossible to diagnose your car over the internet, but my experience tells me you have a weak opti. My dads '94 and my old 95 Z28 did the same thing. See if it misses under load at low rpm under 2k rpm or around 5k+ rpm. If it doesn't pop, miss, buck, or backfire than the opti is probably fine. It's a very hillbilly way of troubleshooting, but is about 95% accurate. With you saying the car sat for about 7 years that's where I put money.
Jeff
Jeff
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Burning Brakes
Joined: May 2002
Posts: 755
Likes: 42
From: Sierra Foothills, State of Jefferson
Looks nice.
May want to measure the fuel pressure at the rail.
You do not need a scanner to pull the codes.You just need a paper clip.
Please look at the FSM book 2,starting at page 6E-6.
Or this source- DTCs with pictures.
May want to measure the fuel pressure at the rail.
You do not need a scanner to pull the codes.You just need a paper clip.
Please look at the FSM book 2,starting at page 6E-6.
Or this source- DTCs with pictures.
Last edited by KurtK; Apr 28, 2022 at 07:44 PM.
Team Owner
Joined: Aug 2008
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From: Rochester NY
St. Jude Donor '09 thru '26
Melting Slicks
Joined: Sep 2003
Posts: 2,270
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From: N. Babylon NY
Good luck!
Melting Slicks
Joined: Jul 2005
Posts: 2,649
Likes: 863
If the two gauges read differently it would be a dead giveaway that you had a bad temp sensor - feeding bad data to the EFI system, which could cause the problems that you're describing. But since your Temp sensor is apparently working - that is unlikley to be the issue.
I'd look at fuel pressure first - then think Ignition System .... (and while it MAY be Opti related - if you are going down the Inition system route - I'd give the coil and the coil driver a good look first. Far easier to get to - far cheaper components, and probably More heat sensitive.
I'd look at fuel pressure first - then think Ignition System .... (and while it MAY be Opti related - if you are going down the Inition system route - I'd give the coil and the coil driver a good look first. Far easier to get to - far cheaper components, and probably More heat sensitive.
Instructor
Joined: Apr 2022
Posts: 142
Likes: 48
From: Central NY State
If the two gauges read differently it would be a dead giveaway that you had a bad temp sensor - feeding bad data to the EFI system, which could cause the problems that you're describing. But since your Temp sensor is apparently working - that is unlikley to be the issue.
I'd look at fuel pressure first - then think Ignition System .... (and while it MAY be Opti related - if you are going down the Inition system route - I'd give the coil and the coil driver a good look first. Far easier to get to - far cheaper components, and probably More heat sensitive.
I'd look at fuel pressure first - then think Ignition System .... (and while it MAY be Opti related - if you are going down the Inition system route - I'd give the coil and the coil driver a good look first. Far easier to get to - far cheaper components, and probably More heat sensitive.
Team Owner
Joined: Aug 2008
Posts: 32,964
Likes: 6,462
From: Rochester NY
St. Jude Donor '09 thru '26
Bought my first c4. 94 with 50k. Had it for a month and it has been an absolute nightmare.
Melting Slicks
Joined: Jul 2005
Posts: 2,649
Likes: 863
Not to hijack OP tread, but my '93 is having the same symptoms as his, starts fine cold, once it gets up to temp or 160+ and higher it shut soff like I turned the key off, both at idle or while driving. Before I have had time to diagnose at length one thing I have noticed is my digital temp will get say up to 160 or higher and my analog is still at 100. So that being the case, maybe my temp sensor is bad and the ECM is cutting off the fuel?
When your car dies - how long before you can restart it ??? Are any codes thrown ??? If possible - right after it dies - see if you have spark at a plug and then see if you have spark at the coil output.
Opti's die in different ways. There is a low resolution output and a high res output from the opti. If one of them dies - the PCM will throw a code. If both go away at the same time - no code. If the Ignition coil or the coil driver die - normally no code is thrown....
Le Mans Master
Joined: Feb 2000
Posts: 9,060
Likes: 214
From: Epping NH
As an electronics engineer when and electronic device dies after heating up it's usually related to a specific component. In the past when I needed to troubleshoot this issue I'd wait until the unit failed from heating up then use freeze spray on each component to find the culprit.
My guess is a sensor is providing false readings once it heats up or their is a connector that is losing contact as it heats up. I would have initially said the ICM & soldier joint, but you said you have replaced it, so I would suggest starting with the basics.
Check your grounds, make sure they are good. Then unplug each connector and make sure they look clean and tightly secure when you put them back together.
Gas in the oil is not unusual, just depends on how much is in the oil and I'm not sure that would cause the car to die after warming up. And I'm hoping your mechanic checked for codes, if not you really need to start there first.
Lastly does the car start up again once it dies or do you have to wait until it cools down? The latter really would point to a failing sensor or bad/loose connector.
My guess is a sensor is providing false readings once it heats up or their is a connector that is losing contact as it heats up. I would have initially said the ICM & soldier joint, but you said you have replaced it, so I would suggest starting with the basics.
Check your grounds, make sure they are good. Then unplug each connector and make sure they look clean and tightly secure when you put them back together.
Gas in the oil is not unusual, just depends on how much is in the oil and I'm not sure that would cause the car to die after warming up. And I'm hoping your mechanic checked for codes, if not you really need to start there first.
Lastly does the car start up again once it dies or do you have to wait until it cools down? The latter really would point to a failing sensor or bad/loose connector.