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Thread: Shudders and random misses

  1. #1
    Member jrhende6's Avatar
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    Default Shudders and random misses

    My 88 Grand Marquis shudders and misses while in high gear. If I step on it to down shift it gets smooth. At idle the car shook. Annoying.

    So I bought spark plugs - Autolite AP5145. Checked gap for 0.50 and swapped them in. Car is much much better but not perfect. Smooth at idle.

    Swapped cap and rotor.

    I could live with the way it feels right now but it still shudders and misses some while in high gear at low speed. Idles smooth.

    My car is old. Any miles I get out of it are free miles. But hey everybody is so helpful here I thought I'd ask for any tips. I do try to keep my costs down to maintain my "free" miles.

    I could replace spark plug wires but they looked ok.

  2. #2
    Road Warrior Kodachrome Wolf's Avatar
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    There's a symptom that can occur called crossfire. The cylinders 7 and 8 are most prone to do it since they're fired one after another, so 7 could light 8 and you get a stumble/misfire.

    Ford likes them routed like this off the distributor:


    Wire separators help to keep things orderly. Essentially you don't want 7 and 8 wires running side by side any appreciable distance. It might also be worth watching the engine bay when its dark and just making sure you don't have any wires arcing out.

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    You could clean your throttle body, as that sometimes causes symptoms such as those. Get a can of throttle body cleaner, a used tooth brush and some shop rags and spray the butterfly and other area's down to get any varnish and carbon deposits out. I'm sure others here will chime in with tips.

  4. #4
    I'm an air-conditioned gypsy gadget73's Avatar
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    how old are the plug wires? If they're original its time.

    86 Lincoln Town Car (Galactica).
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    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

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  5. #5
    Member jrhende6's Avatar
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    Thank you all for the pointers.

    I've looked around at the other posts and since I had a bottle of Gumout Fuel Injector cleaner laying around I used it. Seems to be helping (ie getting smoother with less bucking and missing).

    I'll clean the throttle body when I get a chance (it is gunked up some) and look at the cross fire issue. My wires are pretty new (3 years old).

    Going to reset codes and look at what gets registered from here forward. Am interested in the TPS calibration and a TVC adjustment too.

  6. #6
    Member jrhende6's Avatar
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    Cleaned the throttle body and did the TPS calibration. Along with the Gumout Fuel Injector cleaner I'm satisfied with the way it is running. A tiny stutter at low speed in high gear.

  7. #7
    Member jrhende6's Avatar
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    Quote Originally Posted by Kodachrome Wolf View Post
    There's a symptom that can occur called crossfire. The cylinders 7 and 8 are most prone to do it since they're fired one after another, so 7 could light 8 and you get a stumble/misfire.

    Ford likes them routed like this off the distributor:


    Wire separators help to keep things orderly. Essentially you don't want 7 and 8 wires running side by side any appreciable distance. It might also be worth watching the engine bay when its dark and just making sure you don't have any wires arcing out.
    Thanks. That was a big help.

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