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Thread: misfire and cutout with small gap.

  1. #1
    turbo addict
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    Feb 2010
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    misfire and cutout with small gap.

    Helping a buddy with his shelby z, recently installed +40s, 3 bar, and a cal. We drove it and with the boost turned up to only 15 we started getting some spark blowout. We checked the plugs and found some bosch platinums gapped at .046. I headded home and told him to get some rn9yc's and gap them to .028. Just now he called back saying the car runs like absolute crap now, can't go over 11psi and misfires really bad. I told him to open them up to .030 and try again but he hasnt called back yet. What is going on with that, I've never had problems with rn9yc's at .028?

    His coil is an accel super stock, I ran one for a while with no issues so I don't think that is the problem. Cap and rotor are new and the wires are brand new magacor's.
    Ian Adams Function>Form 1990 shadow scrapped, too rusty:( 1991 Spirit R/T Scrapped, parts sold:( 1989 Turbo Caravan Daily beater with built-[I]ish [/I]​engine slowly evolving into weekend turbo beater.

  2. #2
    Garrett booster
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    Re: misfire and cutout with small gap.

    Try gapping them at a stock .035" and try diagnosing from there. I have not really ever seen a turbo dodge with an inadequate ignition system where spark blowout is an issue. The stock ignition system is more than enough at high performance levels.

    What were the events leading up to these issues? Was the engine ever running good before any modifications?

  3. #3
    boostaholic
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    Dec 2012
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    Houston
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    Re: misfire and cutout with small gap.

    I had an issue where the coil was cracked and it was arcing to the negative pole of the coil and causing a missfire. New coil solved that issue.

  4. #4
    turbo addict
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    Re: misfire and cutout with small gap.

    What were the events leading up to these issues? Was the engine ever running good before any modifications?
    Car was perfectly fine at the stock 11 psi spark plugs were bosch platinum gapped at .046. We added +40s and 3 bar with a tune made by me, again at stock 11 psi it was fine. We upped the boost to 15 psi and I noticed a slight cutout at WOT, I instantly identified it as spark blowout. I then had him install some rn9yc champions and gap them at .028 since he was planning on moving up to 20 psi, those plugs at .028 caused the engine to misfire very badly in boost. He called me back today and he said he bumped the gap up to .040 and the car runs absolutely perfect. Im just wondering why he's needing so much gap? My van runs nearly the same setup besides being 2.5 and I run my plugs at .028 at 20psi with no issues.

    I told him to work on finding the stock E core coil from a newer car and converting it over to use that.
    Ian Adams Function>Form 1990 shadow scrapped, too rusty:( 1991 Spirit R/T Scrapped, parts sold:( 1989 Turbo Caravan Daily beater with built-[I]ish [/I]​engine slowly evolving into weekend turbo beater.

  5. #5
    Hybrid booster
    Join Date
    Nov 2013
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    Nebraska
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    Re: misfire and cutout with small gap.

    Quote Originally Posted by shackwrrr View Post
    Car was perfectly fine at the stock 11 psi spark plugs were bosch platinum gapped at .046. We added +40s and 3 bar with a tune made by me, again at stock 11 psi it was fine. We upped the boost to 15 psi and I noticed a slight cutout at WOT, I instantly identified it as spark blowout. I then had him install some rn9yc champions and gap them at .028 since he was planning on moving up to 20 psi, those plugs at .028 caused the engine to misfire very badly in boost. He called me back today and he said he bumped the gap up to .040 and the car runs absolutely perfect. Im just wondering why he's needing so much gap? My van runs nearly the same setup besides being 2.5 and I run my plugs at .028 at 20psi with no issues.

    I told him to work on finding the stock E core coil from a newer car and converting it over to use that.
    Every vehicle is going to be a little different. Running "nearly" the same set up doesn't mean that what works on your van is going to work on his car. I'm willing to say he may be getting too much fuel and with the smaller gap was having a hard time igniting it. With the larger gap and bigger spark it lit the A/F mixture off better. As mentioned, I'd have him go back to a stock gap with brand new plugs and go from there. Does he have a wideband hooked up to see what the A/F ratio is? Maybe adjust the tune, or FPR to pull back some fuel under boost if it is running rich. And stick with copper core plugs, maybe go to a colder plug if detonation is a concern.

  6. #6
    turbo addict
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    Re: misfire and cutout with small gap.

    Thanks for the input, the wideband is the next addition to his setup. For now its staying at 15psi so he can play a little, the garret is a little smokey so he'll have to play it nice anyway.
    Ian Adams Function>Form 1990 shadow scrapped, too rusty:( 1991 Spirit R/T Scrapped, parts sold:( 1989 Turbo Caravan Daily beater with built-[I]ish [/I]​engine slowly evolving into weekend turbo beater.

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