1. #1
    TrailRatedRN's Avatar
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    Question Engine noise after replacing spark plugs.

    After replacing the spark plugs, I was getting a #5 misfire on the check engine reading. Drove back to the store, exchanged plug & placed the new one while in the parking lot. As soon as I started the engine, I began to hear a sound near the rear passenger of the engine. Sounded like a faint marraca shaking, or maybe someone going "shh, shh, shh, shh" really fast. The sound became faster with increased RPM. No check engine light. I decided to drive home, approx 5 miles from the store. When I got maybe 2 miles away, and at 45 mph, I heard a loud pop, like a balloon busting, and now the sound is amplified by 2,000 times. It's horrid. The engine still runs and accelerates. I coasted the rest of the way home, gentle as possible on the accelerator.

    I have 06 LJ, I6, 4.0, automatic. I was just doing my 30,000 maintenance.
    I am new to the engine world and don't know much, so talk in kindergarden terms here.

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    sounds like it could be an exhaust leak but I can't possible imagine why that would be happening after changing spark plugs. also was the pop you heard something like a backfire pop or something breaking pop?

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    Re: Engine noise after replacing spark plugs.

    If I had to choose between breaking and backfire, I would say backfire. It was very much like a balloon popping. Really, I would say, exactly like a balloon popping, only much louder. The current noise, the one that went from "shhh, shhh, shh" and is now amplified by 2,000, is certainly on the passenger side toward the rear, but I am not certain if it is toward the top or the bottom. It's so damn loud.

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    Did u gap the plugs to the required specs?

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    Re: Engine noise after replacing spark plugs.

    I was worried when you first posted that perhaps you had the wrong plugs and they popped the top of the piston or something similarly horrible. But from your description of the sound, it sounds like something blown in the exhaust system. Should be easy to find that. Gasket somewhere, perhaps?
    Just Enjoy Every Possibility!

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    Smile Re: Engine noise after replacing spark plugs.

    Champion came pregaped @ 0.035. I do not have the tool to confirm that they r correct.

    I decided to check the number 5 (start @ the source, when I first heard the noise, right?). The f'n plug was waay loose. IDK what happened in the parking lot. I could swear I got it tight enough. Maybe the rubber inside the socket was slipping. Maybe I'm just a weakling. Who knows. It was not a sparking noise that I heard, so I don't know what the noise was. Can air leak around the plug?

    Anyway, I tightened the sucker down good and... tadaa, no noise, no check engine. Hope it stays that way. Thanks for listening.

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    Glad you got it fixed, yes a very loose plug will allow blow by on the exhaust stroke and will also suck air past on the intake stroke.

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    Re: Engine noise after replacing spark plugs.

    Good to hear you have resolved the problem. A couple of things to remember:

    1. The 4.0L 6-cylinder engine uses a one-piece coil rail containing three independent coils. Although cylinder firing order is the same as 4.0L engines of previous years, spark plug firing is not. The 3 coils dualfire the spark plugs on cylinders 1-6, 2-5 and/or 3-4. When one cylinder is being fired (on compression stroke), the spark to the opposite cylinder is being wasted (on exhaust stroke). Intake and/or exhaust leaks can cause some really strange noises.

    2. When you say, "I tightened the sucker down good," the correct torque value is 22 Ft. Lbs.

    3. I always use a small amount of anti-seize on the plug threads to assist with their removal. Helps to keep from breaking insulators.
    -Phil

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    I used anti seize, but I do not have a torque wrench. I have asked for one for my birthday (this month in case you want to buy me something). I am slowly building my garage. Do you believe that the the exact torque on the plugs is imperative to smooth function?
    I have to use a jack to get to my oil pan D:

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    Re: Engine noise after replacing spark plugs.

    Quote Originally Posted by TrailRatedRN View Post
    I used anti seize, but I do not have a torque wrench. I have asked for one for my birthday (this month in case you want to buy me something). I am slowly building my garage. Do you believe that the the exact torque on the plugs is imperative to smooth function?
    Go for the correct torque - spark plugs are one thing that you don't want to over tighten and strip or break.

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    Re: Engine noise after replacing spark plugs.

    This is from the Factory Service Manual for my '03 and it is good advice...

    "Always use the recommended torque when tightening spark plugs. Incorrect torque can distort the spark plug and change plug gap. It can also pull the plug threads and do possible damage to both the spark plug and the cylinder head."
    -Phil

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