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Thread: Gt40P Heads Spark plug Gap.

  1. #1
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    Gt40P Heads Spark plug Gap.

    I did a complete tune up on the 1990 mustang and its developed a miss, breaking up when going about 2000 rpm. I double and triple checked my firing order and timing and both are good. My question is has anyone ever gapped a spark plug too much and had problems. I've messed with plug gap before in my s10 with a 350 and never had any issues. Now this car has gt40p heads ,engine is a 302 and I'm running autolite 764 plugs in it which old owner had in it. I gapped them at .054like I have on my other mustangs. Did a google search and people are all over the place with the gap with these heads and plugs. Anyone run a setup like this or have any suggestions , Going to pull out whatever hair I have left.

    Did plugs ,wires ,cap and rotor. double checked plugs yesterday and gaps are what I set them at.
    Last edited by jclose11; 09-10-2019 at 09:04 AM.

  2. #2
    Just spank it!!! Viper_ed's Avatar
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    Make sure the wires are fully seated on the plugs and distributor cap.

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  3. #3
    No Traction due to Paxton PaxtonShelby's Avatar
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    Did you use a dab of dialectric grease on the plug tips and cap tips?
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  4. #4
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    Yes I did. I bought new plugs today going to throw another set in even thou I just put new ones in. Co worker said he has had new plugs that were bad new out the box, and I got wire looms coming so the wires are not touching.

  5. #5
    Hi! I'M DAKS #1 BITCH! TooFast98Cobra's Avatar
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    There are a bunch of cracked porcelain ngk plugs out there currently.

  6. #6
    Junior Member TGP500's Avatar
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    Do you still have the original plugs and are they the same thread length? Years ago on my 94 I swapped out the GT40 heads for aluminum heads and used the stock plugs. Turned out the plugs were too short to reach all the way into the combustion port and causing a misfire like you describe.

  7. #7
    Tripedalist yeahloh95's Avatar
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    don't be afraid to gap them down some and see if that helps I run .028 on my boosted set up
    Troy
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