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PROM questions

C4ROADMAN

Member
Joined
Feb 11, 2009
Messages
9
Location
Florida
Corvette
1990 White
PROM questions and now EGR question '90 C4

I put an ad in the parts section, but maybe I should just ask.

I recently bought a 1990 corvette with 26k on the clock. I noticed when I bought it, that it idled a bit rough in gear (automatic tranny), but if I put it in neutral it was much smoother at a stop. Driving was fine...just the idle problem in gear.

I called the dealership where I bought it from and told them about it. They said bring it back for the mechanic to look at it. The first repair shop took a look and said one of the plug wires was bad, so it was swapped out. Since the wire was no good, the cylinder had not been firing properly and the plug was fouled up. So the mechanic cleaned up the plug and sent me on the way. During my drive back to the house, the car sputtered and died.

I got the car towed to another repair facility that the dealership wanted. The new mechanic eventually changes all the plug, the computer, and fuel pump with a bill of around $600. So I go pick it up and after about 25 miles, the car sputters. I hit the gas...no throttle response, and it stalls. I could start the car up, it would idle but if I revved it, the RPMS would go up and back down leading to a stall out. I tried this a couple times and then the car would not run at all. So another tow back to the mechanic.

Well I called today to check the most recent attempt at fixing it. The mechanic now says that the PROM is bad and he is attempting to find one off a 1990 Automatic somewhere.

The question is, do I need to find a 1990 Corvette used PROM (which seems hard to do) or is their an alternative? Is there a place that sells blank PROMS and can program for a 1990 Corvette? I haven't seen any sites selling used PROMS, only piggybacks that I need to plug the stock PROM into.

I am lost at this point. Can someone help?
 
It came on one time for a few seconds. But that was on one of the drives where the car ddin't break down!
 
Try TPI Parts , I know he has new GM memcals for '90 Camaro's

TPI PARTS
 
The check engine light has only been on one time and that was when the car was running right but the tech says the PROM is bad.

Hmmm.

Well...good luck.

I'd be interested to hear what the bottom line is on this case. Can you post again once the car is running better?
 
Low milage so it should not be but have your optispark checked. Sounds a bit like a ignition problem.

Steve
 
Might be a long shot but you could have a bad catalytic converter might be broken inside or mostly plugged. If the main cat breaks inside and the inside turn sideways it could plug it.
Find a place to attach a vacuum gauge to manifold vacuum.
watch to see if vacuum drops especially at steady 1500 RPM.
Plugged catalytic converter will also make them run warm.
Usually the warmer a plugged converter gets the more it effects the engine.

Glenn
:w
 
PROM Questions

I know I'm late to this thread, but I agree with the gentleman who thought this to be an ignition problem. however it seems to me that the second shop you took the car to, never tried to diagnose the problem, they just started replaceing parts. I am not a professional mechanic, but through experience I've learned to start with the most simple thing it could be first. So I would start with all electical connections having to do with the ignition system first. then move on to the fuel system if need be! It could be something as simple as a loose connection. I hope I have been some help;shrug
 
i am just going to toss out what happened on my 68 mustang resto mod.i dont know if it effects gm ttrannies ,like it does my c-4 .first the car started idling like crap ,cked everything then a bud said ck the tranny fluid ,it was 3 qts low . filled it up and poof she was back to her old self . just thought to share
 
With engine idling tap the MAF with a screwdriver handle if it stumbles or dies its the MAF.
 
Newest update:
ECM replace with a reman. and a new PROM. Vehicle throws a 32 code occasionally after a decent drive (actually it popped up right in the location I broke down last time).

Now it seems to have a "miss" while idling in Park, about every few seconds it seems to lose a small amount of power and then it catches up again. While attempting to increase throttle during Idle (PARK), there is a hesitation and then it revs up.

I know CODE 32 is the EGR and thanks to the purchase of a Factory Repair Manual (best $50 spent on Amazon!) I seem to be getting somewhere in terms of learning about this car (and diagnosis).

Anyone else have EGR problems like this with their cars? I know the manual states that the EGR should not be a major factor at PARK and NEUTRAL, but the replacement seems to be a bit of a job (removing the PLENUM).

Anybody else run into this situation? Thanks!
 
have someone ck you cat converter. i am thinking there is loose ceramic in it causing a cork in your system
 
Newest update:
ECM replace with a reman. and a new PROM. Vehicle throws a 32 code occasionally after a decent drive (actually it popped up right in the location I broke down last time).

Now it seems to have a "miss" while idling in Park, about every few seconds it seems to lose a small amount of power and then it catches up again. While attempting to increase throttle during Idle (PARK), there is a hesitation and then it revs up.

I know CODE 32 is the EGR and thanks to the purchase of a Factory Repair Manual (best $50 spent on Amazon!) I seem to be getting somewhere in terms of learning about this car (and diagnosis).

Anyone else have EGR problems like this with their cars? I know the manual states that the EGR should not be a major factor at PARK and NEUTRAL, but the replacement seems to be a bit of a job (removing the PLENUM).

Anybody else run into this situation? Thanks!

Check out the article in this link for more information on EGR operation, note in particular paragraph #5.
EGR Systems: Operation and Diagnosis
 
C4ROADMAN, Search this site for more info on how a negative pressure EGR operates. I posted info not found in the factory service manual on the L98 EGR. A bad EGR can indeed cause issues in any gear. The ECM should not signal the EGR solenoid in N or P or at idle in D, but that doesn't mean that the valve is working/closing properly. A vacuum pump is a handy tool to have. After checking out the EGR, my suggestions would be to remove and clean the throttle body and IAC, and check the minimum air speed. IAC is used by the ECM to maintain a programmed idle speed. I've found that the IAC can build up carbon, especially if an oil based filter (i.e. K&N) is used.
 
also check rhe vacuum tree (EGR solenoid) attached to the inner bolt on the thermostat housing, it is a plastic line inserted into a rubber housing. After 20 years that plastic gets brittle and will break.
 
Had a chance to look at the car today. All the vacuum tubes look good. Even switched in another ECM and prom.

Old ecm and new ecm, the car won't even idle right. I hold the throttle open a little and after about two seconds, the rpms drop and the engline stumbles, and sometimes it catches back up on RPMS. Other times, it just stalls.

For the first time today, while idling, the car died on its own.

As I was running out of daylight, everytime I even gave it a little gas, the car wanted to die. I tired driving down the block and the car did not want to run when given gas.

Argh!!!

I am working on getting a vacuum tool this weekend.
 
Newest update.

Brought it to a shop with experience in Corvette specific repairs.

Diagnosis: 3 injectors have low ohms. Recommended replacing all 8 since he will have everything off anyway.

Estimate: $350 parts, $500 labor, + spark plugs, etc total just under $1000.

Aargh
 
Why not do it yourself ? There are many threads on here from people who have and it seems to be a straight forward job and will cost you a fraction of that estimate (not quote I see ). Roger.
 

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