Thread: *HELP*car stutters and feels like misfiring above 50% throttle

Was out tuning getting my fueling and afr dialed. On my last run I drove around letting the car relearn a bit on the shift pressure then made my way onto the freeway. Once I got onto th on ramp and saw no cars coming up nor ahead I gotten on it from a 55mph roll. I got the 4-2 downshift and glanced at my LS1M and saw no knock and my PLX WB was in the 11.0-11.1 whereas my commanded is at 11.4. pleased at my somewhat accomplishment I slowed down and decided to do another run. Once I got the 4-3 downshift the car bogged and felt like it was misfiring. I slowed down and just cruised the speed limit and the car didn’t appear to suffer any other misfire. I gotten on it again and once I went past ~50% throttle the car would shake and feel like it was misfiring. I pulled over and popped the hood and didn’t hear any sort of knocking or metal banging so it sounds like the motor’s fine.

I pulled into a gas station and powered my pathetic laptop and the powertuner to turn back on P0300 for looking at misfires. After doing a partial flash I went back onto the freeway and scanned for any misfires by cylinder and revolutions via LS1M(my laptop is slow and cant process the info transfer). I gotten on it again and I THOUGHT I saw a blip on cylinder #5 but it wasn’t showing a whole lot. I cant remember how many miles I put on my AL103 which are gapped at 0.040 nor the plug wires which is not the original 155K miles but they are OEM. The car drives and shifts fine if im below ~50% throttle. I can hit boost at ~30% without feeling the car hesitate and stutter. I don’t have a garage space to check, but I’ll plan to find a friend nearby who can lend me some warm shelter/garage. I am thinking about picking up a set of new AL103 plus and maybe plug wires. Any suggestions or does anyone has had a similar encounter?

just when the car was getting close to where i want it this **** happens.

just swapped out the plugs and they all look fine. they were actually AL104s gapped at 0.045. took it out again and this time it was stuttering/misfiring anything above ~70% throttle. i did notice the #2 plug wire was slightly meltetd since it was rubbing against the rear header. it wasnt large or bad loking but could it be a bad plug wire causing it?


another update:
another update, i thought i was running the MAF area in PE too lean causing the car to misfire but after i increased the areas slightly a bit and scanned my IPWs are 18mS but i noticed when i scanned misfires per revolution after 60% thorttle it was showing 10 whereas the misfire per cylinder did not show the specific cylinder misfiring, unless the pcm cant scan it at that speed and load. any other ideas at the moment? im thinking of swapping out all the plug wires just in case tomorrow. do u think i have a chipped piston ? other than the plug wires im out of ideas on what it could be.



need some help :-(

you're right on #1, its not tune related as i added more fuel but still had a stutter/misfire
#2, how would i check if the coil pack(s) gone bad? i had them reaplced with another set of used lower mileage 1-2 years back from ed morad.

thanks for the info, i basically increased fro the 7650 up to 11500 by 1.2% plus added an add'l +2 so its linear. i might have my old/oem coil packs somewhere in the garage i could swap in.

Originally Posted by FoSHO99

Try gapping the plugs to .054

You got a powertuner, revert back to stock tune except for your lq4 maf table and injector tables and see what happens.

i never had an issue with the plug gappings in the past and im using 42.5# injectors since late of last year. the only thing i changed was leaned the MAF out more up in the area where im in WOT. the last run i did b4 this issue came up i ran zero knock and my wb was showing a steady 11.0-11.1. im gonna try and swap my coil packs out sometime this weekend. i was planning on going to the MACGP local car group in KOP for a dinner get together but i might skip on that

Could be the ICM too if you've never replaced that...just something that hasn't been mentioned