Hi all,

I’m looking for some help. About a month ago, I took my 1992 Corvette LT1 base model coupe into a touch less laser wash which sprays the entire car (even the under carriage). I have taken the car to the wash many times before and have never had an issue even after I replaced my optispark distributor, ignition coil, and spark plug wires about 2 years ago. Back to the wash, the car was on during the wash. Once I finished, I turned the car off to wipe it down for about a half hour. Upon turning it on again, it started idling a little rough (little misfiring). When I put the car in drive or reverse (putting a load) it starts to idle even rougher with more signs of what seems to be misfiring as the car hiccups. Then, when driving it I had really poor acceleration where I’d have my foot down on the gas and the car sounded rough with even more misfiring. On the way home it was misfiring so bad in drive I felt i had to keep giving it gas as the car continued to hiccup even worse. I jumped the engine codes and saw that there were none on the dash board (via jumping the engine pins A & G). So, having no idea as to what to do I removed the MSD distributor I had installed and sent it back to the company to fix (not knowing if it was broken or not). They rebuilt the distributor (new cap, rotor, bearings, opti sensor etc.). The repair tech told me the distributor should be timed to the stock settings and once it is installed then, the distributor should be keyed to the cam shaft (theoretically eliminating timing issues). However, there is a timing screw as seen in the image attached incase I do want to adjust the timing. Continuing with this mystery, I reinstalled the rebuilt distributor and made sure all the wires were plugged in tight/correct. I turned the car on and found that I still had a rough idle but, the acceleration got better and I felt the car had more power. It still had the same issue idling and the misfiring in drive/reverse where it hiccups but it did improve slightly. So, next I replaced the spark plugs. After replacing the spark plugs, the car was stronger again but still had issues misfiring and is not running right. It happens at a cold start and when warmed up. I am not sure what to do next. I asked my mechanic and he said he would look at it in two weeks but thinks it’s the optispark. Again, I haven’t seen the ignition low pulse codes or any engine codes. I also checked that the plugs worked by pulling each fuel injector sensor one by one and noticing a response from the cylinder.

Please let me know your thoughts, if there’s something else I could test along with how to test it.

Additionally, does anyone in here live in Massachusetts and might be able to help take a look at this?

 

First, MSD optisparks are a crapshoot, so best of luck. Currently the best optispark on the market is one from optisparksolutions on eBay, or Petris Enterprises. "Timing" on an optispark is nonsense; they're designed to be a fixed timing, and are controlled by the ECM. MSD adding a screw to "adjust" the timing is another bit of silly nonsense. Set it to '0' and leave it there. There's a reason why no other optispark on the planet has such an adjustment.

Second, no codes means there's nothing electronically abnormal enough for the car to think there's a problem. That could still be the opti, sure, because something wrong with the rotor won't trigger an engine code. It could also be the ignition control module failing (have you replaced it? if you did, did you put heat sink compound on it?). It could also be a bad coil, though it appears that you've replaced that already.

Best of luck.

 

Little update, I replaced my MSD optispark with a new rebuilt one by the OptiDoctor which has my original Mitsubishi sensor in it. The car is still running poorly and I'm having trouble diagnosing what exactly is wrong with the car. Specifically, when the car is in idle it appears to maintain a steady RPM; however, the exhaust sounds deep and it gives the impression that it may be misfiring. When the car is put in drive and I go for a ride, I am unable to accelerate quickly and it gives me the impression that the car is running in "limp mode"; the exhaust also sounds deep when I drive. When I attempt to give it throttle, I get little to no acceleration even when I attempt to fully open the throttle; I get little to no response and it sounds like it is misfiring. Lastly, this occurs when the car is hot or cold.
I have replaced the spark plugs, spark plug wires, ignition coil, and optispark distributor. So, I don't believe this can be ignition related and I don't get any engine codes when I attempt to read them off the electronic dashboard of the car.

Have you or anyone else experienced an issue like this? I'm open to any ideas or suggestions.

Please let me know what you think I should test and how to test it.

Much appreciated,

Thank you!

 

I would check the fuel pressure. Also check for vacuum leaks, IACs, and TPS. For the latter you may need a data logger.

Good luck

 

Did you replace the Ignition Control Module? That wasn't in your list.

As I said already before, no codes means that there's no sensor feedback problem. As far as the ECM is concerned, all sensors are connected and reporting data, so there's no electronic issues to be had. This means the problem is more mechanical in nature. It's something that the ECM has absolutely no insight into, because it's trusting that the readings from its sensors are all correct. While the issue could still be a sensor that is lying to the ECM, it's probably best to check mechanical possibilities first.

Have you checked fuel pressure at the rail? Might be a good next step. If we assume the electronics are okay, then the engine really needs air, fuel, and spark. Spark you've pretty much got covered (though ICM could still be a possibility), so next would be fuel. After checking pressure, checking the resistance of each injector to make sure they're in spec would be good as well.

If this were a 94-96 I would say to plug a laptop in and log data. On those cars it's pretty easy. On a '92 it's a tad more complicated, but if you are interested in trying it out, I'd be more than happy to walk you through the process. Datalogging can show us things that are otherwise invisible, such as exactly what data the ECM is operating on milliseconds at a time. Occasionally there'll be something in that data that'll give you an "a-ha!" moment. For example, my '94 gained a mysterious surging issue at idle that normally would make you think a vacuum leak or brake booster failure. But after datalogging, it became obvious that the culprit was a bad signal from the opti only at low RPMs that, for only a few milliseconds, made the computer think the car was idling at 4000 RPM instead of 550 RPM. This led the IAC to move wildly, which caused the car to surge. Trying to figure that out without a laptop would've been...pretty troublesome.

As always, best of luck. If you don't already have a factory service manual, acquiring one might be a good idea. They're only like $22 on Rockauto.

 

This is good advice. I will add to this, change the fuel filter. The car is old enough that if the filter has not been changed, it could have blockage.

 

have you checked your fuel? Perhaps water got into the tank from the filler area during wash...


Did you wash the underside of the car? Long shot but what about a collapsed cat?

 

I had a low mile 92 that was missing and had poor acceleration. It didn’t have any codes. The fuel pressure seemed ok. I changed the opti. It ended up being two bad injectors. You can unplug your injectors, one at a time and note any change in the engine idle. Mine ended up being the #2 & #8 injectors were bad.