Missing turned to random cutoffs
Thread Starter
Racer
Joined: Jun 2017
Posts: 343
Likes: 18
From: Newport News VA
Missing turned to random cutoffs
Long time no post! 89 L98 ZF6 with presumed LT4 hot cam and PCM of NC tune.
Car had sat for a little over a year while I finished up my 68 BBC Chevelle and moved to another state, life, etc.. Car sat in my garage, not outside in the elements. I had treated the gas with some ISO Heet before she sat for a while and I fired it up and let it idle every couple weeks until it got to temp. Never any issues at idle. Finally had some time to throw at her and got her registered here in SC and got her out on the road again. It had a misfile that would only present when going above light throttle, otherwise it cruised just fine. I chalked this up to bad gas and ran the tank down to a 1/4 and threw some 93 in there as well as some injector cleaner. Problem persisted. It seemed to get worse the longer I drove, classic ICM style where it got worse as it got warmer. I had a spare new ICM and replaced it. Took it out after the ICM replacement and it popped a couple times but then cleared up and ran awesome. Then...as I was cruising in 6th, engine died but still had full electronics to the car; service engine light flashed a couple times and then went out. I pulled off on the shoulder, cycled the key off and back on, fired right up and got back on the road; no popping and no service engine light. About 8 mins later, turning on the road behind my house, as it idled down in neutral as I approached the turn, it died again. Again, cycled key off and back on, fired up and finished the 300 yards to my garage. Car idled in the driveway just fine. I haven't had a chance yet to strap the ole FP gauge to it and see if I am getting pressure drops. Pretty much every sensor on the engine is newer and the FP relay was replaced about 3 years ago along with the pump itself with a new Delco unit. My primary suspicions are a dying fuel pump or intermittent failing relay. Thought stream is leading me to think the mis/popping was dropping pressure and even though I changed the ICM, I had a flash where the pump was working properly but then started to crap out. Otherwise the car has been dead nuts reliable after I cleaned her up in 2017-2018. I wanted to pick some brains and see if there is anything else I am missing? Failing coil seems like a stretch? As always, appreciate the assist.
Car had sat for a little over a year while I finished up my 68 BBC Chevelle and moved to another state, life, etc.. Car sat in my garage, not outside in the elements. I had treated the gas with some ISO Heet before she sat for a while and I fired it up and let it idle every couple weeks until it got to temp. Never any issues at idle. Finally had some time to throw at her and got her registered here in SC and got her out on the road again. It had a misfile that would only present when going above light throttle, otherwise it cruised just fine. I chalked this up to bad gas and ran the tank down to a 1/4 and threw some 93 in there as well as some injector cleaner. Problem persisted. It seemed to get worse the longer I drove, classic ICM style where it got worse as it got warmer. I had a spare new ICM and replaced it. Took it out after the ICM replacement and it popped a couple times but then cleared up and ran awesome. Then...as I was cruising in 6th, engine died but still had full electronics to the car; service engine light flashed a couple times and then went out. I pulled off on the shoulder, cycled the key off and back on, fired right up and got back on the road; no popping and no service engine light. About 8 mins later, turning on the road behind my house, as it idled down in neutral as I approached the turn, it died again. Again, cycled key off and back on, fired up and finished the 300 yards to my garage. Car idled in the driveway just fine. I haven't had a chance yet to strap the ole FP gauge to it and see if I am getting pressure drops. Pretty much every sensor on the engine is newer and the FP relay was replaced about 3 years ago along with the pump itself with a new Delco unit. My primary suspicions are a dying fuel pump or intermittent failing relay. Thought stream is leading me to think the mis/popping was dropping pressure and even though I changed the ICM, I had a flash where the pump was working properly but then started to crap out. Otherwise the car has been dead nuts reliable after I cleaned her up in 2017-2018. I wanted to pick some brains and see if there is anything else I am missing? Failing coil seems like a stretch? As always, appreciate the assist.
