Thread: Misfire only at idle on #2

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  1. #1 Misfire only at idle on #2 
    GT Level Member sugaryuk's Avatar
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    After L32 swap into my GT, I'm getting a crap load of misfires only on #2 and only at idle. I get up to 200 misfires (using aeroforce gauge) while idling and once under load while driving misfires go to 0 and misfires return when back to idle. When motor is warm--it still happens, but amount of misfires appear to go down. Swapped out plug (looked fine-not wet), wire, coil and injector-- no help. Vacuum is steady at 19-20, motor has about 50 k on it and didn't do this before swap--but motor sat for about 4 months (may-sept) in donor car. Took it out on hwy for over an hour-running the piss out of it hoping to get it hot enough to cure it--no luck. So question is...why only at idle? Would a valve issue not misfire all the time? Could a pitted cam lobe cause this? Head gasket? Any ideas out there?
    02 GT- L32/Gen V, 3.3 mps, zz 1.9's, N*, slp front to back, OverKilled, 180 tstat, 104's, K&N cai, lowered with GMMP susp, 12" PBR brakes
    75 Pro-Street Vega-- Blown 383 stroker with Nos fogger system
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  2. #2 Re: Misfire only at idle on #2 
    Perma-Banned! JK LOL Explicit_Spade's Avatar
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    Start with the basics:
    Possible causes

    - Faulty spark plug 2
    - Clogged or faulty fuel injector 2
    - Faulty ignition coil 2
    - Fuel injector 2 harness is open or shorted
    - Fuel injector 2 circuit poor electrical connection
    - Ignition coil 2 harness is open or shorted
    - Ignition coil 2 circuit poor electrical connection
    - Insufficient cylinder 2 compression
    - Incorrect fuel pressure
    - Intake air leak

    and make sure your MAF is good.
    Quote Originally Posted by W-Body Store
    Remember, GM engineers didn't take into account your need for speed.
    Daily Driver: 06 Grand Prix GT / 9.4:1 CR / IS3 Heads / Ported Gen V / ZZP Headers / HPT Pro / Pulleys: 4.25, 3.8, 3.5, 3.4, 3.2, 3.0, 2.9, 2.7
    Projects: 86 Monte Carlo SS / 98 Sonoma / 74 Honda CB750
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  3. #3 Re: Misfire only at idle on #2 
    GT Level Member sugaryuk's Avatar
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    Quote Originally Posted by Explicit_Spade View Post
    Start with the basics:
    Possible causes

    - Faulty spark plug 2
    - Clogged or faulty fuel injector 2
    - Faulty ignition coil 2
    - Fuel injector 2 harness is open or shorted
    - Fuel injector 2 circuit poor electrical connection
    - Ignition coil 2 harness is open or shorted
    - Ignition coil 2 circuit poor electrical connection
    - Insufficient cylinder 2 compression
    - Incorrect fuel pressure
    - Intake air leak

    and make sure your MAF is good.
    Like I said, I've already swapped out all the parts with known good parts and I've checked the connections- they appear to be clean and making good contact. I can't hear or find any leaks. One thing I forgot to mention is that when I started it up for first time since install, after a minute or 2 engine started making somewhat loud ticking noises. (didn't have oil gauge hooked up yet--dumb move) so I shut it off and checked dip stick-- didn't look like oil hadn't moved much so I banged on oil pump housing thinking that spring might of been stuck after sitting for a while. Restarted it and noise went away and now dip stick was wet. Engine appeared to run fine after that-- no noise or smoke. After gauge install, pressure is 60 at load and about 45 idle--seems good. So possible temporary oil starvation causing damage to cam lobe or rings? Haven't done compression test yet, but performance doesn't seem an issue- car is pulling hard with no problems.

    Also...can a faulty MAF cause misfires to only one cylinder?
    02 GT- L32/Gen V, 3.3 mps, zz 1.9's, N*, slp front to back, OverKilled, 180 tstat, 104's, K&N cai, lowered with GMMP susp, 12" PBR brakes
    75 Pro-Street Vega-- Blown 383 stroker with Nos fogger system
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  4. #4 Re: Misfire only at idle on #2 
    Perma-Banned! JK LOL Explicit_Spade's Avatar
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    Quote Originally Posted by sugaryuk View Post
    Also...can a faulty MAF cause misfires to only one cylinder?
    As strange as it sounds, it has happened. There's a several page thread somewhere on here where someone was troubleshooting a cylinder 2 misfire and a new MAF fixed the problem.


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    Quote Originally Posted by W-Body Store
    Remember, GM engineers didn't take into account your need for speed.
    Daily Driver: 06 Grand Prix GT / 9.4:1 CR / IS3 Heads / Ported Gen V / ZZP Headers / HPT Pro / Pulleys: 4.25, 3.8, 3.5, 3.4, 3.2, 3.0, 2.9, 2.7
    Projects: 86 Monte Carlo SS / 98 Sonoma / 74 Honda CB750
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  5. #5 Re: Misfire only at idle on #2 
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    IIRC just unplug the MAF it should go to base tables, that should help diagnose it. You didn't mention if you did a compression test on Cylinder 2. A minor leak or tear could cause idle issues that go away under acceleration. How do you know the coil is good or the ICM is?

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  6. #6 Re: Misfire only at idle on #2 
    GT Level Member sugaryuk's Avatar
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    Quote Originally Posted by nox View Post
    IIRC just unplug the MAF it should go to base tables, that should help diagnose it. You didn't mention if you did a compression test on Cylinder 2. A minor leak or tear could cause idle issues that go away under acceleration. How do you know the coil is good or the ICM is?

    Sent from my ASUS_Z00TD using Tapatalk
    I'll try unplugging the MAF to rule it out. Haven't done a compression test yet--no tester...probably be my next purchase. I swapped 2/5 coil with 3/6 (which wasn't showing any misfires) and the misfires stayed on #2 cylinder. Haven't swapped the ICM out yet but I have a spare GT ICM--know if they are interchangeable? Like you mentioned, starting to think I might have a leak, possibly intake related?
    02 GT- L32/Gen V, 3.3 mps, zz 1.9's, N*, slp front to back, OverKilled, 180 tstat, 104's, K&N cai, lowered with GMMP susp, 12" PBR brakes
    75 Pro-Street Vega-- Blown 383 stroker with Nos fogger system
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  7. #7 Re: Misfire only at idle on #2 
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    LiM are known for going bad on these cars. Headgaskets not as common. ICM should be interchangeable from non-supercharged. Typically a misfire that doesnt move rules out the coil. Pull the plug and confirm the gap/wire, I know some times the angle for getting plugs in can microcrack them.

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