In early March '11, I purchased an '89 Corvette. It ran fine until Easter Sunday and that’s the last day I’ve been able to drive it. I’ve had it in the shop two times in the last month because it will stall without any warning. The first attempt to fix it, the shop did a “major” tune-up, replacing the spark plugs & wires, the ignition coil, the cap & rotor, and the in-line fuel filter. This didn’t cure the problem, so about 2 weeks ago, I put it in the shop again. This time, they made sure that all the previous work was done correctly. It was, but the car still had the same issue. So, they attempted to diagnose the problem by swapping out the ignition module, spark control module, and even the ECM. This didn’t work either. After having the car more than a week, they finally ended up replacing the whole distributor assembly and declared the problem solved. It wasn’t. On the way home from the shop, it stalled again. I had to have it towed home and it’s been sitting in the driveway ever since. While they had it, they did discover that the #6 injector wasn’t working. So, last weekend, I replaced that myself. That didn’t cure the problem either. In fact, after doing the repair, it idles rougher now than it did before, and it still “died” about 10 minutes after getting it running. I’ve even checked all the ground-wire junction blocks under the hood, thinking it might be a loose connection. Through all of this, it has never set any fault codes in the computer’s memory.
Anybody have any other ideas? It doesn’t seem to matter whether it’s sitting in the driveway at idle, or out on the street. It can run 5 minutes before stalling, or several hours. There’s no rhyme or reason to when it does it and I’ve got 44 lbs. of fuel pressure at the rail when it does this. Normal pressure is supposed to be between 40 and 45 lbs.
Well, the stalling problem seems pretty predictable. I would carry a can of starting fluid and an extra spark plug in the vehicle. The next time the engine stalls take the starting fluid and spray it into the intake system and if the engine runs and stalls it’s a fuel issue. If that don’t work, pull a plug wire off a plug and insert the exta plug into the wire and lay it on the engine. Now look for a bright blue spark while cranking the engine. If the spark is more of a yellow color or nonexistant it’s an ignition problem.
I can’t remember for sure, but I believe this is of the vintage of the crappy mass airflow sensors. One thing to try if this car has a MAF would be to unplug it when the car is acting up. Or while it’s running you could use a screwdriver handle and tap on the MAF to see if you can make it stall.
Someone has been guessing on your car at your expense for sure. Plugs, wires, cap, rotor, and a fuel filter are not going to cause a random stalling and they have resorted to changing out not only all of the electronic ignition parts but also the ECM.
Questions.
Did they have any basis at all for changing those ignition parts or was it a WAG? (wild axx guess)
You state that you have 44 PSI of fuel pressure. Does this mean 44 PSI at the exact second in time when the engine will not start?
(Point being that a fuel pump can be a hit and miss thing and considering the age of the car an erratic pump is a good potential cause of this problem.)
When I first started having this issue, I took it to the shop the first time. When I arrived and went inside to tell the service writer what the symptoms were, he sent out a tech to take a look. The tech couldn’t get it to start, so he did some initial testing in the parking lot and discovered that there was no spark. He had to have 3 or 4 other techs help him push it into a service bay. That is why they did the tune-up.
They didn’t replace the ECM. They swapped it out for one that they knew worked correctly, in an attempt to cure the problem, but it didn’t make a difference, so they put the original one back in. They didn’t charge me for a new ECM.
After the second trip to the shop, when they replaced the distibutor, I don’t have a problem with being able to get it started. I have a problem with keeping it running. As for the fuel pressure, it is 44 lbs at initial pressurization and remains steady with the engine running. Since none of the fuel injectors appear to be leaking, the pressure remains at 44 lbs even after the engine stalls. It takes several hours for the pressure to start dropping. After it stalls, it always starts right back up, although it usually doesn’t stay running for a long period of time.
Since I’m also a member of the Forums at Corvette Action Center, the MAF test was already suggested and attempted. Although, I didn’t try tapping on it with a screwdriver.
Aside from the stalling issue, the car has a very rough idle as well. Once it gets warmed up enough to go into closed-loop, the engine is running so rough that it shakes the car and the idle is only 600rpms. At higher rpms, I feel like there is a misfire, but I can't tell which cylinder it's coming from. When I first bought the car, none of these things were an issue.
With a no spark situation and seeing as how they’ve changed the entire ignition system maybe the problem is related to a failing ignition switch . (electrical part)
I’ll rummage in some of my manuals for a schematic just to make sure there’s nothing unusual in the way the wiring is laid out and post back tomorrow.
Like OK4450 stated I suspect the trouble is due an interruption of power to the ignition system. It is the first thing that should be checked when having an ignition problem. You may want to rig a small test light at the power connection to the ignition so you can monitor it while you are driving.
Sounds eerily familiar to me. I had a '91 that had similar symptoms to your final paragraph. Those symptoms can be caused by many different kinds of problems. I ruled out compression, fuel and finally ignition problems before having to set it aside for some time. Later, the car was mostly stripped to be restored and the true problem discovered. With the dash out you could hear the vacuum leak at the brake booster.
We currently have a '91 Vette in our shop that’s had us tearing our hair out. Wound up finding a shorted injector that was drawing down the others. Went through a lot of hassle to change it, & less than a week later, another injector’s doing the same thing. Game plan is now to replace the remaining 7 injectors.
CBM,
Have you made sure the voltage getting to the injectors is okay and not too high? There may be a issue with current limiting resistors in the injector circuit. I sounds to me the coils are being damaged because the drive current in the coils is too high for some reason. If that is the case the new injectors will become damaged also.
@OK4450
Were you able to find the schematics for the ignition switch? I’m beginning to think the stalling issue is with the VATS system since it doesn’t die out like it’s starved for fuel, it shuts off like someone turning off a light switch. It’s immediate. There’s no spitting, sputtering, back-firing. It just stops.
Sorry for just clean forgetting about this one. Keeping in mind that I’m by no means an expert on these cars and never, ever really trusting a wiring schematic, here’s my opinion. I do agree with you that it’s likely electric in nature and not fuel related.
The schematics showed the VATS system only controls the starter enable relay; meaning it will affect the engine starting but no effect once it is running. The diagrams showed that tying the ECU, ignition module, etc into the VATS did not occcur until a few years later so if the schematic is right I would rule a VATS problem out.
I’m thinking of a problem in a common power source and this means between the battery positive terminal and on through to the ECU, ign. module, etc. This could be a faulty ignition switch problem or a distribution terminal problem. Follow a heavy wire from the battery positive terminal and it should route to a common distribution terminal under a plastic cover. This is also called a junction terminal. Sometimes these look clean but once the nut is removed and the cable ends are visible there may be a scale or corrosion on them which can lead to a poor or erratic power connection. It’s not a bad idea actually to go in every few years and clean these just for the heck of it.
About 15 years ago while on vacation in Colorado I registered at a hotel one evening, came back out to the parking lot, and found my SAAB would not start; no warning lights, radio, starter motor operation, nothing. Inspection of the junction terminal showed a grayish looking scale over the cable ends but it didn’t look bad enough to be a problem. However, it was a problem in spite of the somewhat clean appearance.
Popped the cable ends loose, scraped them lightly with a pocketknife, and voila.
Up to that incident and after it this kind of problem had never surfaced and the point here is that something as small and seemingly insignificant as this can be a puzzling headache at times. Always check the simple stuff first. Hope that helps anyway.