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  1. #1
    Petty Officer 3rd Class
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    Jul 2005
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    Default Thunderbolt IV cap and rotor

    When it's dark and damp I can see arching across my distributor cap and any substantial amount of water dripping through the engine hatch will cause my engine to miss. I'm assuming that it's probably time to replace my cap and rotor right? I think it's been a good 18 years. It's a thunderbolt IV ignition on a 5.7 L 1988 merc.I purchased a cap and rotor kit and it all seems fairly simple looking at the parts included, but I've never worked on this system before. Can anyone fill me in on the steps involved?Thank you,nat

  2. #2
    Supreme Mariner Haut Medoc's Avatar
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    Jun 2004
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    seattle, wa
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    Default Re: Thunderbolt IV cap and rotor

    Pull off the old rotor & install new one...Install new dist cap.....Replace the ignition wires most likely....Check timing.....It is that simple....I'd be surprised if the timing changes at all...Should be 8* btdc @ idle....Make sure #1 wire goes on #1 plug...Firing order is 1-8-4-3-6-5-7-2 clockwise.....JK
    Disclaimer!: In my inexpert opinion......

  3. #3
    Petty Officer 2nd Class
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    Default Re: Thunderbolt IV cap and rotor

    I assume you have some experience with engine tune ups but if not a good process to follow is to pull one wire at time off the distributor cap and plug it into the corresponding location on the new cap. That way there is no risk that you will plug one into the wrong spot on the cap. same is true if you are replacing the wires (and from your message it souunds like you better replace them)

  4. #4
    Supreme Mariner
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    Sep 2003
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    Default Re: Thunderbolt IV cap and rotor

    get the service manual. its actually a bit more involved than posted above. the thunderbolts use loctite to retain the rotor. if you follow all the steps you will most likly be directed to remove the distributer. if you dont just be very careful the loctite does not drip into areas its not supposed to be. a heat gun or small propane torch will aid in rotor removal.unless the last guy in the cap did not loctite it.
    no tech questions by PM, they wont get answered.
    you have to be trusted by the people that you lie to .

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