4.0 Knocking - JeepForum.com
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post #1 of 3 Old 05-16-2011, 07:50 AM Thread Starter
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2000 WJ 
Join Date: Mar 2011
Location: Alexandria
Posts: 10
Wj 4.0 Knocking

I've looked at several dozen threads about knocking, but none seem to address my issue, so here goes:

Specs: 2000 WJ Laredo, 4.0, 93K, selec-trak trans, oil changed about 2K ago.

Basic problem: Engine has begun knocking during low rev acceleration, both from standing and when shifting into second gear. Only happens when the engine is under load--not when at standstill. Does not appear to happen when shifting into higher gears or at highway speeds.

Interesting tidbit: Doesn't happen when gas tank is full, just when it gets below about a 3/4.

Sounds and feels a lot like dieseling, but doesn't continue to happen after engine is turned off.

This does NOT sound like the loud clacking in some of the videos posted, which some have suggested is piston slap, bad rod, etc. (Then again, I'm listening from inside the vehicle while moving.) More of a standard pinging/knocking you get in some cars with crap gas. (I usually use Shell or Exxon, so assume it's not a crap gas issue--though I did use No Name brand once in a pinch a few weeks ago.)

I can feel a slight drag on acceleration while this is happening, but that goes away once the revs increase and the knocking goes away.

Tried some fuel additive (injector and fuel system cleaner), but no help. Have not tried oil additive, as I have always felt that those are more likely to mask a problem than cure it.

Is this more likely (a) a GET THEE TO A MECHANIC NOW situation, or (b) more of an annoyance that is not urgent? Or????

Any thoughts welcome.


AnotherOne is offline  
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post #2 of 3 Old 05-16-2011, 10:38 AM
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1999 WJ 
Join Date: Oct 2004
Location: Russellville, ar
Posts: 1,323
can you post a video of the sound you are hearing? I am thinking it may not be valve train related like in my videos, but either drive train or engine "carbon" buildup.

Try pouring about a half can of seafoam through the intake and put the other half can in the tank. Make sure it is not the evap purge valve you hear on the driverside fender.

Does it do it when you put it in drive, hold brake and give it gas?
jclaudii is offline  
post #3 of 3 Old 05-18-2011, 11:16 PM
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2004 WJ 
Join Date: May 2011
Location: Columbia
Posts: 1
Unfortunately, I do not know the answer to your issue, but my 2004 Jeep Grand Cherokee appears to occasionally experience a problem that is similar to what you are describing. My Jeep occasionally knocks when the engine is under low acceleration and when it is first started. The issue only appears to occur after the Jeep has been towing a heavy load. The problem immediately stops after the engine accelerates to a higher RPM. Any thoughts?
Garland207 is offline  

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