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Thread: Engine Knock At Low RPM

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    Engine Knock At Low RPM

    I have a 2018 Cummins (144,000 miles) with 68RFE transmission, and everything is stock.

    I recently had an oil leak behind the timing chain, which the dealer fixed. I also had an SCT tuner running the 20hp tow tune.

    When I'm driving about 40 mph and let off the pedal and let the rpm drop down around 800 rpm and then lightly touch the pedal, the motor knocks extremely loud for about a second. It sounds like the fuel is igniting early.

    I took the tuner off, and it still does it. Can this be caused by the dealer removing the timing chain our what could cause this?

    The dealer can't find any problems with it.

    It has been there a week, and they told me to drive it until it gets worse, but I'm afraid it will damage the motor.


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    Re: Engine Knock At Low RPM

    Quote Originally Posted by whiteryker View Post
    I have a 2018 Cummins (144,000 miles) with 68RFE transmission, and everything is stock.

    I recently had an oil leak behind the timing chain, which the dealer fixed. I also had an SCT tuner running the 20hp tow tune.

    When I'm driving about 40 mph and let off the pedal and let the rpm drop down around 800 rpm and then lightly touch the pedal, the motor knocks extremely loud for about a second. It sounds like the fuel is igniting early.

    I took the tuner off, and it still does it. Can this be caused by the dealer removing the timing chain our what could cause this?

    The dealer can't find any problems with it.

    It has been there a week, and they told me to drive it until it gets worse, but I'm afraid it will damage the motor.
    Is it throwing any codes?

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  5. Top Of Page | #3

    Re: Engine Knock At Low RPM

    It has no check engine codes, no rough idle, or anything that would indicate a problem.

    Just the loud knock that is about 4-5 times louder than the engine.

    I had the computer reflashed at the dealer and started running a cetane fuel additive, and I haven’t heard it do it again (yet).

    I’m hoping that fixed it.


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  7. Top Of Page | #4

    Re: Engine Knock At Low RPM

    Still knocks.

    Could it be a knock sensor?


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