So, I was having problems last year after I bought my car last year. It’s a 40th anniversary, and has almost 200k now. Couldn’t figure out the issue last April, and it ended up being the opti, so I swapped it, and it was all gravy for a long time. Fast forward to last month. Started getting issues with dying after it’s been running for 15-20 minutes but it usually started right back up. It also started dying on me while in the middle of cruising the freeway at 75. I also get a heavy fuel smell quite a bit. After much denial, I believe it to be the optispark again. I took to a well known local corvette guy. I had a ton of oil leaks, and at the end of the day we dwindled it down to the opti. So that was changed along with all my gaskets and seals in the motor, and many various other things like radiator, ball joints, shifter, shifter cable, tune up, etc. Spent a lot for all this. Went to go pick up the car when it was finished and they had the car running when I got there. Didn’t sound all the great if I’m being honest. Still sounded like it was running a little rough. But it was running. They said they had it running for a good 30 minutes. They hopped in to show me, revved it to WOT and it stalled. They said it hadn’t done that. They messed with several things under the hood, wires, etc, and nothing really seemed to help. We started talking about what I replaced recently. I had just done my alternator with 124 amp, but we noticed the terminal post for the battery loop stripped and just free spins. After I mentioned that, we went to go start the car again and it was completely dead. Jumped it with a battery pack and it started right up. Went WOT and it died again. Shut it off, let it sit for a minute, started it again, and let it sit. It died after about 10 minutes. Started it back up again, let it run, and it ran for like 35 minutes. Still didn’t sound 100%, maybe 80%? But it didn’t die.

We started talking about what previous owner did.

From what I was told, the previous owner changed the fuel pump, optispark, coil, wires, plugs, and water pump. Didn’t change the ICM though. I actually have an ICM sitting here that I can go change.

my mechanic said to come home and swap the alternator and the ICM and it should run right. Keep in mind I had been at their shop for a couple hours by now trying to figure this out, and I live about an hour and a half away. I don’t really have too much more to spend to figure this out either. I took the car and headed home. I drove it home normally, didn’t have any issue except for(again) when I got on it at WOT. I got on it to open it up, wasn’t really paying attention to the RPMs but it was probably around 5k-6k, and you could feel it sputter then die, and service ASR came on. Started right back up and drove it home fine the rest of the way with service ASR.

So my spark is good. I have new opti, plugs, and wires. Not going to be an air issue. I don’t have any vacuum leaks, and just had all my gaskets done. Also no current DTC. There were 4 saved codes. 2 were for LCD/LED dimming, another was for passkey, and the other was 41 for loss of ecm serial data.

Does this sound like ICM or alternator? Sounds more like fuel to me. But I feel like if it was an issue with fuel, it would have an issue idling, right? Matter of fact when I put it in neutral it runs nice and smooth. If my IAC or map sensor or something was bad, I’d also get a code, correct? I know a bad opti can present without a code.

I have a snap on mt2500, but I’m still trying to figure that out. Also going to test fuel pressure and injectors on Wednesday, my only off day.

 

A stumbling problem is almost always fuel or air... so I think your assessment is correct that it's not timing since it would probably give you issues at more than only at WOT... though it is possible that it COULD be the ignition coil. The odd thing that I'll never understand is why GM went with the ignition coil they did on the LT1. You have the exact same ignition coil as what's on my V6 Fiero from the mid 80s. At 5,500 RPMs... My V6 Fiero would "run out of breath" because it's unable to produce the amount of spark needed at that high of an RPM. Replacing it with a higher output ignition coil usually makes a significant difference in the higher rpms (though has literally no change in the low to mid rpm). I'm usually a HUGE fan of OEM GM parts, but this is an area where GM is less than great. Things like MAP sensors, ICMs, etc... original GM is the only way to go... everything else is garbage, but you'll definitely see an improvement with something like an Accel Supercoil replacement (though their reliability is often questionable). Nevertheless... I have seen coils slowly fail like that, but it's really uncommon... they usually just fail outright.

As with the ICM... I definitely don't think it's the Ignition Control Module, because those too usually just fail outright. I do sometimes see them fail where you can start the car when cool... but after the car warms up, it fails... usually because of a lack of thermal paste under the ICM mounting location, or some heat-expansion sensitive failure that's already occurred in the ICM... but never seen the kind of symptoms you have coming from an ICM. ... THIS though... "It died after about 10 minutes. Started it back up again, let it run, and it ran for like 35 minutes." could be ICM heat / cold issue.

I tend to concur with you that it could be a fuel issue... since it works perfectly fine, except at the higher rpms... in which case you're possibly not getting enough fuel. When was the last time you ran something like Seafoam through your tank? I do wonder about the fuel pump though. Is it original? My thoughts are that it's slowly giving up... like, is the car harder to start? If it's all original, the flexible tube or vibration isolator (if original) would be likely failing at this point because of all the ethanol in our fuel... and it may be leaking. I'd concur that you should check the fuel pressure.


On another note though... at 200k miles, the car is probably due for a lot. Something to think about, but at 200k miles, I generally either give a car away, or completely mechanically restore it at that point. Nearly everything in the engine bay is starting to get tired and every single thing in the engine bay is on a failure clock. Usually when you rebuild an engine, and replace every sensor and component with new stuff (including accessories), you more or less "reset the clock" for everything so it's like having a new car again (at least in that regard). Just something to consider on what you want your long-term plans to be with the car...

 

I was told the fuel pump was replaced not too long before I bought it. But there’s no receipts, and the guy did all his own work. So take that for what it’s worth. The guy said my engine was still good. Compression test was good, he took care of my vacuum leaks, put new belts on it. I think I replaced the coil last year, I can’t remember. I know I had a coil in my hand because I ordered it with everything else when I did my optispark. Can’t remember if I swapped it though if I’m being honest. I want to say I did though.

The part about the coil in your Fiero makes sense, but I didn’t have a problem before I took it to the mechanic.

I actually had originally intended to have the guy rebuild it for me, but apparently I can’t afford it, like $10k+. I might as well go get a C5 or something.

Never have run seafoam or anything through it. I need to learn how to use my snap on reader, I’m sure it has some kind of information. Really hoping it’s not an ECM issue.

 

OHM test your fuel injectors individually. They should all be the same within a few tenths of an ohm, 16 is the typical number but due to minor variations in multi-meters, they might read anywhere from 14-17ohms. Our cars have batch fired fuel injectors and one bad one can cause total failure in fuel delivery. And then they will recover like nothing's wrong.