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'00 XJ slight engine knock

gw204

NAXJA Forum User
Location
St. Leonard, MD
Guys, I've asked this of my dealer every time my Jeep has been in for service, but it never occurred to me to ask here. I've always been given the A-OK. The Jeep goes in for an alignment on Wed. so I'm going to ask again. But now that the warranty has expired, it wouldn't surprise me to get a very different answer....

Now for the details....

My Jeep is an '00 and was bought new in 8/00. It is equipped w/ the 4.0 and AW4. I currently have just over 57k on the odometer. Since it was new, I have noticed that, occasionally, the 4.0 I have produces a what sounds like a slight knock at idle. Oil changes have always been performed within the recommended interval using 10-W30 dino oil and no fancy snake oils or additives have ever been used. Oil pressure holds between 40 and 45 on the highway and just over 20 at idle when warm. She has held these pressures since new. I am planning on changing the oil pressure sender soon anyway. Never overheated, run w/out oil or anything out of the ordinary. She still runs extremely well but sounds almost as bad (occasionally) as my '88 w/ 213K. I do tow approx. 3500 lbs. pretty frequently though, but I wouldn't think that would cause this.

I was just wondering if anyone else has experience similar noises. The 4.0 in my mother's '96 Grand Cherokee is much, much quieter than the one in my XJ. Are there any differences between the two motors that would cause the '96 4.0 to be quieter.

Are the later 4.0 motors subject to piston slap or do you guys think I may be experiencing bearing failure very prematurely??? Again, it doesn't sound bad all the time, just occasionally.

This is really driving me crazy.

Thanks for any info you can provide.

Brian
 
It may not be an engine knock at all. There is a purge valve for some part of the emissions system that's mounted to the firewall, and at idle this valve makes a sort of muted "chuff-chuffa-chuffa" sound that can be quite worrisome. However, it's normal and doesn't hurt anything. My 2000 Classic has it, but I've driven other 2000s in which it isn't noticeable. Mine is an early 2000, so they may have relocated it or used softer mounts on later examples.
 
My 99 Sport does the exact same thing at idle only. Has since the day i got it. I knew it wasn't a real knock but i couldn't nail down where the noise was coming from. Good to know.
 
In my 97 it's a crack at the "Y" in the exhaust manifold. Makes a clicking knock type noise.
 
Both the 90XJ and the wifes 02WJ 4.0's rattle a little at idle. Kinda a lite tap-tap-tap, goes away with a little throttle. This is the second engine on the XJ, first one lasted 160K with the same noise from day 1.

MATY - Turn up the radio.

Rev
 
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