I've just bought a 100% bone stock 91 formula 305 tpi with a 5 speed manual. It seemed to run fine and we took it 200 miles with no issues until I took our friends out for a drive and I ran it a bit harder shifting at about 4,500 rpm 2 or 3 times and slowed down for a turn and pushed in the clutch and got ready to down shift but then it suddenly died. I got it to start again if i gave it some gas and it would then idle at about 600 rpm like some kind of limp mode. I replaced the tps sensor, the iac valve, the distributer rotor and the icm. Gave us a code 42 before we threw those parts at it and didn't fix the issue of it dying after aggressive acceleration. We even adjusted the idle with the screw and it still died the same way. Could it be fuel related? And why would I get a code 42? It runs perfect after sitting for a while and it will rev up to 5k rpm just fine. Only dies after it gets near that rpm range under load then dies shortly after but will start again into some limp mode. Any idea if it's fuel related or something?

Sorry for the long winded explanation, haven't seen any similar problems on the forums and it has to be my daily so I really need it to work. Any help would be greatly appreciated, thank you so much for your time!

Subscribed. I’ve experienced this similar problem with my 91 Formula, also a 5 speed. Only happened a few times but annoying when it does.

Yeah what's weird Is when i drove it 200 miles it got all the way up to hot operating temp and held it no issues at all. And every time without fail, it dies after i push it up to 4500 rpm but only after i slow down and push in the clutch before I get a chance to shift into first it dies.

I had a similar problem with an LT1. Turned out the ignition module finally died off and I replaced it with a good original one, problem went away. No idea if it's the same thing for you but that's my experience.

yeah, that's what's weird I replaced the ignition control module and it still has the same issue

Sounds like high load (high cylinder pressures) are taxing the ignition system and possibly causing a shutdown of the ICM..... Start with plugs and wires. Too much plug gap or poor wires will require more voltage - especially at high cylinder pressures - high voltage heats up the coil and ICM needlessly. Gap all the plugs to 0.035

GD

wow thanks for the great info! The previous owner did plugs and wires but I will definitely check the gap and replace if they're crusty. I'll do the wires too, but could it also be the knock sensor? Because when we started it after it died the first time it ran like it had a big cam because of the retarded timing. But after some sitting it started and ran like normal until it died again after pushing it and it went into that 600 rpm mode.

Unplug the knock sensor. But generally no the knock sensor isn't going to cause a stall. Check and adjust the base timing and make sure the wiring to the ECM including the EST bypass connector is solid.

GD

Great I'll try running without knock sensor and the timing was dead on when it was checked 3 days ago. Also where is the est bypass located? Any pic or link would be greatly appreciated since I've seen some but they aren't consistent in the placement. Thanks for the info, I'm gone for a week so I'll try all of this when I get back and give you an update!

The timing should be checked and set with the EST unplugged so I'm not sure how you could have checked it and know it's dead on.....

The EST is a single wire (brown with black trace) weather-pack connector generally located around the passenger strut tower or inboard of the AC evap box on the harness running around the back of the engine towards the distributor.

GD

yeah I forgot to mention that right before we bought it and a shop looked at it and checked the timing and cleaned the est connector.

Quick update: haven't got back yet but I've read about code 42 being triggered from a no start which is what happened before I tried pumping the gas. And I read that the spark gets advanced by the est circuit at high rpms. Is there a chance that the spark is getting advanced and isn't coming down with the rpm causing a stall when in neutral after high rpms under load? Any troubleshooting flow charts or other answers? Thinking it also could be the pickup coil and related connections.

Maybe a bad or weak fuel pump or clogged fuel filter
that's my guess

Advanced timing wouldn't cause a stall. It would run increase the RPM and make it unable to idle.

And there's really no way that can happen. If it loses the EST signal it will revert to locked base timing (which is 6 degrees stock).

Pumping the gas does nothing on fuel injection. There's no accelerator pump.

GD

every single time it wont start, you could crank it for 15 seconds and it wont start but if you pump the gas while cranking it starts but idk what causes this.

yeah it starts after a stall only if I pump the gas while cranking. Then you have to keep up the throttle to keep it running for a bit then it runs fine. Then it runs really rich for a bit.

Have you checked your fuel injectors? My engine would shut down once it reached operating temp due to one or two fuel injectors overheating (I think it was the coil inside the fuel injector).