Changed Plugs, Now Running Like Crap

Discussion in 'Fox 5.0 Mustang Tech' started by 93flstang, Jun 30, 2013.


  1. 93flstang

    93flstang New Member

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    yesterday i changed my ngk v -powers and threw in some autolite coppers with the factory gap of .54 into my 5.0. i drove around town testing them out and the car drives like complete crap, has rough acceleration and it even starts up kind of slow and doesn't idle as high with the choke on. yes i have a 670 Holley street avenger with an electric choke on my motor. i am running a stage 2 trick flow cam and trick flow heads, full exhaust and a weinstealth intake etc...

    i checked the sp wires and the boots are in good shape, so are the conductors. i dont know why the hell its acting this way. any ideas? should i just go back to the ngk v powers? i heard that autolites were always awesome though.

    curt
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  2. mikestang63

    mikestang63 Mustang Master

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    Sounds like you either swapped a wire or the wire is not on the plug. Did you tighten up all the plugs? It's easy to forget to tighten up one. Only other thing I can think of is you have a bad plug but that is rare.
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  3. creektrack

    creektrack Member

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    Maybe this can help...

    [​IMG]

    Sent from my SPH-L720 using Tapatalk 2
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  4. clement

    clement Founding Member

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    Did u lay a plug wire on the headers?
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  5. 93flstang

    93flstang New Member

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    no i did not, but i removed each wire and plug one at a time to ensure no confusion with the firing order. i manually screwed them in by hand then tightened them down with the socket/ratchet. i just ordered some accel 8.5mm to replace my 9mm ford racing ones. they looked kinda old, but if that doesnt correct the issue than i am just going to buy ngk v powers again and put them in.
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  6. 93flstang

    93flstang New Member

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    could it be that i have aftermarket heads?
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  7. creektrack

    creektrack Member

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    Do you have access to the old plugs? Check the gap on them, it may have been set different than stock...

    Sent from my SPH-L720 using Tapatalk 2
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  8. clement

    clement Founding Member

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    those ford 9mm wires are garbage. that's probably the problem.
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  9. MFE92

    MFE92 Active Member

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    Yeah, but it sounds like he didn't change the wires, and they were running just fine before the plug change. There's very little likelihood that the plugs themselves are the issue, unless one or more of the plugs is damaged (dropped, perhaps? Cracked the porcelain?). If that's not the case, then the next most likely thing is one or more of the wires is not fully seating on the plugs, or has been damaged by the headers, or the 5/6 wires are touching each other, or one of them is arcing on the dipstick tube.
    #9
  10. clement

    clement Founding Member

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    ive had some of those wires have issues after removing them from plugs.
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  11. 88LX5.Oh

    88LX5.Oh Advanced Member

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    TFS heads need long reach plugs and stock heads use short reach, correct?
    On my Eddy heads I ordered a set of E3 plugs for a stock 88 Mustang and went to put them in and realized they were way too short and had to get long reach ones. Just something to think about :shrug:
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  12. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    The odds are that one or more of the spark plug wires is broken inside. I have had a boot stick to the plug insulator an the resultant twisting and tugging needed to get it off broke the wiring at the boot.

    Get out you ohmmeter/DVM and measure the resistance of the spark plug wires. The wires should have 1000-4000 ohms per foot of length.
    Examples:
    A 1 foot wire should read between 1000-4000 ohms.
    A 3 foot wire should read between 3000-12,000 ohms.

    Look inside the distributor cap for evidence of cracking or traces where the spark jumped to ground.
    Check the rotor for the same sort of cracks or traces where the spark jumped to ground.

    Wait until night or find a dark place. Get a spray bottle of water and set it for a fine mist. Start the engine and spray the mist around the wires and distributor. Watch for sparks and glow around the wires.

    If you had the fuel injection system that the car originally came with I could tell how to find the problem using the computer's built in diagnostic tests. Carbs aren't that smart.
    #12
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