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

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  1. #1 *HELP*car stutters and feels like misfiring above 50% throttle 
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    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.
    old setup-Z7 Turbo Kit w/T66, A2A I/C, stock cam & valvetrain/LS1 MAF/Ported 99TB/PowrTuner/AFC/Devils Own/LS1M Scanner/PRJ FP/42# Injs=12.3@118mph street tires -
    (Sold)BACK TO M90 Vs cam w/3.5" pulley/meth/25* timing+bolt-ons
    01 Z28 A4 HP-self-tuned, LTs, FTRA, 3600stall 12.3@112mph
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  2. #2 Re: *HELP*car stutters and feels like misfiring above 50% throttle 
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    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 :-(
    old setup-Z7 Turbo Kit w/T66, A2A I/C, stock cam & valvetrain/LS1 MAF/Ported 99TB/PowrTuner/AFC/Devils Own/LS1M Scanner/PRJ FP/42# Injs=12.3@118mph street tires -
    (Sold)BACK TO M90 Vs cam w/3.5" pulley/meth/25* timing+bolt-ons
    01 Z28 A4 HP-self-tuned, LTs, FTRA, 3600stall 12.3@112mph
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  3. #3 Re: *HELP*car stutters and feels like misfiring above 50% throttle 
    TDCRacing
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    I don't even have to read you're post to tell you


    1 that this is most probably not tune related
    2 that you're coil packs are probably bad. Or at least one.
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  4. #4 Re: *HELP*car stutters and feels like misfiring above 50% throttle 
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    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.
    old setup-Z7 Turbo Kit w/T66, A2A I/C, stock cam & valvetrain/LS1 MAF/Ported 99TB/PowrTuner/AFC/Devils Own/LS1M Scanner/PRJ FP/42# Injs=12.3@118mph street tires -
    (Sold)BACK TO M90 Vs cam w/3.5" pulley/meth/25* timing+bolt-ons
    01 Z28 A4 HP-self-tuned, LTs, FTRA, 3600stall 12.3@112mph
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  5. #5 Re: *HELP*car stutters and feels like misfiring above 50% throttle 
    TDCRacing
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    I'm not sure there is a way to test them. I'm sure there is suppose to be a ertain amount of resistance between coils but i'm really not sure.


    One other thing. If you can look at you're maf flow table as a graph veiw to make sure it does not look like a mountian...Largs peaks and valleys will also cause a car to jeark real bad if the peaks or valleys are high or low enough.
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  6. #6 Re: *HELP*car stutters and feels like misfiring above 50% throttle 
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    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.
    old setup-Z7 Turbo Kit w/T66, A2A I/C, stock cam & valvetrain/LS1 MAF/Ported 99TB/PowrTuner/AFC/Devils Own/LS1M Scanner/PRJ FP/42# Injs=12.3@118mph street tires -
    (Sold)BACK TO M90 Vs cam w/3.5" pulley/meth/25* timing+bolt-ons
    01 Z28 A4 HP-self-tuned, LTs, FTRA, 3600stall 12.3@112mph
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  7. #7 Re: *HELP*car stutters and feels like misfiring above 50% throttle 
    youtu.be/xhrBDcQq2DM FoSHO99's Avatar
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    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.
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  8. #8 Re: *HELP*car stutters and feels like misfiring above 50% throttle 
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    Quote Originally Posted by FoSHO99 View Post
    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
    old setup-Z7 Turbo Kit w/T66, A2A I/C, stock cam & valvetrain/LS1 MAF/Ported 99TB/PowrTuner/AFC/Devils Own/LS1M Scanner/PRJ FP/42# Injs=12.3@118mph street tires -
    (Sold)BACK TO M90 Vs cam w/3.5" pulley/meth/25* timing+bolt-ons
    01 Z28 A4 HP-self-tuned, LTs, FTRA, 3600stall 12.3@112mph
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  9. #9 Re: *HELP*car stutters and feels like misfiring above 50% throttle 
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    I have the same issue in my 2003 Monte, still working on a fix... no idea what else to try, swapped all TB sensors, did relearns... The car will drive perfectly when cold, or when the PCM is reset, but then quickly deteriorates... I'm going to try another tune file, and reflash, but any other ideas?
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  10. #10 Re: *HELP*car stutters and feels like misfiring above 50% throttle 
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    want to test the coils....got an easy way. shut car off and take one wire off one coil. start car. repeat process for other two coils. u should hear a constant, non stuttering spark and that spark should jump right to the bold holding the pack. thats for a parcially bad to very bad coil. if still nothing stands out test ohms between electrodes and again in the slots under the coil pack. all readings should be close to the same for each pack. congrats uve just tested ur coils the hilbilly way and the right way.
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  11. #11 Re: *HELP*car stutters and feels like misfiring above 50% throttle 
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    just beacuse the plugs look good doenst mean they r. spend 12 buck, get a cheap set of autolites and install and try again. ive seen plugs that look and test great still be bad. ill send u one to prove it if u want. test ur wires too. if u r now taking off like all holly hell thanks to a tune u may have had one sit one something hot or rub against something sharp. good luck
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  12. #12 Re: *HELP*car stutters and feels like misfiring above 50% throttle 
    The Blue One blueguy's Avatar
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    Could be the ICM too if you've never replaced that...just something that hasn't been mentioned
    Sold WBody's: '03 Blue GTP/'98 Green GTP/'98 Silver GT/'05 GXP
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