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  #1  
Old July 31st, 2003, 07:44
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paul_s paul_s is offline
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front of engine knocking

89XJ, 4.0, auto. There's a slight knock coming from the front of the engine, but its exact location i'm not sure of. It's not very loud but it sounds like metal on metal. I can only hear it at idle and when I raise the RPMs it doesn't go away, but it doesn't seem to get any worse. Anyone ever hear this kind of noise? Any clues as to what it might be? Thanks!
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Old July 31st, 2003, 09:30
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AZ Jeff AZ Jeff is offline
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The 4.0 in line six is known for having "piston slap", where the piston knocks against the cylinder bore slightly. It sounds sort of like a lifter, but less metallic, and more of a dull knock. Is this what you are hearing?

If so, then don't worry about it. Piston slap is NOT fatal to the 4.0, as the engine can go 100K+ miles sounding like this.

For those of us raised on Chevy and Ford 6 cylinder engines, it's very disconcerning at first, but it grows on you..........
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Old July 31st, 2003, 09:46
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I also have an '89 4.0 and have similar knocking at times. I first noticed it 3 or 4 years ago, and it comes and goes. It's always at idle and can sound like a diesel at times! It also only occurs at idle. I think I've noticed a relationship to which oil and filter I'm using, but could be way off there. The good news is that after all this time nothing has blown apart!
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Old July 31st, 2003, 10:55
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satan satan is offline
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Here's a thought...
... paul_s, have you inspected your harmonic ballancer (main pulley) lately? The 4.0 loves to eat the dampening material and the pulley walks off of the hub (sometimes toward the front cover with a knocking noise)
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Old July 31st, 2003, 11:11
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I was hoping it's not that, but I'm not ruling it out. I'll take a look at that this weekend when we replace the serpentine belt. Thanks!
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Old July 31st, 2003, 11:50
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Piston slap is more common on early 90s 4.0L engines. If the noise comes and goes away randomly, it might be just a noisy lifter (more frequent on AMC engines).
It can be caused by an oil starving lifter (sludge in oil passages) or by a failed lifter (replace).
I have an 88 that has occasional lifter tick for almost 5 years now. I am not in a hurry to replace it.
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Old July 31st, 2003, 12:45
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I have occasional lifter ticking too. My ticking is definately a function of the condition of my oil and brand of oil filter. The front engine knock is a much deeper sound and comes from lower on the block. It is especially loud when listening from the drivers side front wheel well. I feel so special to have both...
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Old July 31st, 2003, 15:06
XJEEPER04 XJEEPER04 is offline
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Did, it just start doing it all of a sudden?? because if the engine got a little warm one day driving then it could be a lifter...My 89 4.0 does this. I also have another xj that has some piston slap and the engine only has 30,000 on it.
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  #9  
Old July 31st, 2003, 20:14
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Matthew Currie Matthew Currie is offline
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Another knocking that falls just about in the same frequency range as piston slap is a bad water pump. My 95 has piston slap, and the water pump practically went to pieces before I realized that that was what was making it "seem a little louder than usual."

Piston slap by itself should lessen a little when you speed up, and often gets better when the engine is hotter and the pistons have expanded.
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