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Sigh...need new insight

T

Tampa_XJ

NAXJA Forum User
Location
Detroit, MI
Ok been trying to solve this clacking/rattling noise I'm getting on the XJ and I'm failing miserably thus far.

Info: 93 XJ 4.0/auto/231 with around 250K Miles on it 3" lift, 60psi oil pressure on start, runs between 25-40 once warmed up. Temps run fine, no other running issues.

Symptom: Produces a rattle/clacking noise when idling and is worse with the a/c on. Noise goes away as soon as you touch the gas. Sounds a lot like a rod knock.

Stuff done thus far: Dumped the oil and checked for metal particles and other tell tale signs of metal wear ( oil was clean). Pulled valve cover and checked lifters and rods for defects and such(all were fine and tight). Dropped oil pan to check for rod bearings even though my oil pressure was fine(all were tight and good considering mileage). Removed inspection plate and checked converter bolts(3 were tight 1 required a half turn). Checked for loose accessories, dented/bent exhaust and skidplates, etc.

My opinion: At first I assumed it was a bad rod bearing, but with my oil pressure there is no way it could be that. The fact that the noise only occurs at idle and goes away when on the gas also kinda makes me skeptical of anything internally. Usually the noise would increase at the same speed as the engine if it were a rod knock/piston slap/ or lifter tap. The noise does seem to come from the oilpan/tranny area.

Any opinions or directions to go would be greatly appreciated. To be honest the thing runs fine, I just can't deal with having a random noise that isn't supposed to be there.
 
What rpm is it idling at ? with ac off and with ac on ?
There is a knock sensor on the side of the block under the header, at least I think there is for your year. Also the older 4.0's tend to knock at low rpm.
 
what about your motor mounts? tranny mount even? if one of those is bad, could cause some odd rattling....
 
can't recall the exact idle rpms, but it was damn near the other 2 xjs I have. Mounts are all good, hehe thats one of the first things I checked..
 
I have the same sort of problem with my 1994, and still haven't been able to pinpoint it. The only difference so far is that yours gets worse when you put the AC on...

I'm thinking mine might have something to do with a cracked exhaust manifold, is yours cracked too?

Have you checked it with a mechanic's stethoscope?

:)
 
I had the same noise on my 86 2.5L. It turned out to be the timing chain. I replaced the chain, gears and the dampener (it was a kit) and the noise went away.
 
Tampa_XJ said:
Ok been trying to solve this clacking/rattling noise I'm getting on the XJ and I'm failing miserably thus far.

Info: 93 XJ 4.0/auto/231 with around 250K Miles on it 3" lift, 60psi oil pressure on start, runs between 25-40 once warmed up. Temps run fine, no other running issues.

Symptom: Produces a rattle/clacking noise when idling and is worse with the a/c on. Noise goes away as soon as you touch the gas. Sounds a lot like a rod knock.

Stuff done thus far: Dumped the oil and checked for metal particles and other tell tale signs of metal wear ( oil was clean). Pulled valve cover and checked lifters and rods for defects and such(all were fine and tight). Dropped oil pan to check for rod bearings even though my oil pressure was fine(all were tight and good considering mileage). Removed inspection plate and checked converter bolts(3 were tight 1 required a half turn). Checked for loose accessories, dented/bent exhaust and skidplates, etc.

My opinion: At first I assumed it was a bad rod bearing, but with my oil pressure there is no way it could be that. The fact that the noise only occurs at idle and goes away when on the gas also kinda makes me skeptical of anything internally. Usually the noise would increase at the same speed as the engine if it were a rod knock/piston slap/ or lifter tap. The noise does seem to come from the oilpan/tranny area.

Any opinions or directions to go would be greatly appreciated. To be honest the thing runs fine, I just can't deal with having a random noise that isn't supposed to be there.
Click to expand...

Sounds like the A/C compressor clutch bearing is going bad.
 
yea I was thinking about the a/c clutch or the timing chain...it just throws me off that the noise seems to come from the bottom end towards the back of the motor more so then the front... I'm going to get out the stethescope this weekend and see what I can't pinpoint...
 
Remove the serpentine belt. Its best to do this with the engine cold of course, and run it for a couple of minutes. I had the same knocking noise, and I immediately thought the motor, turned out to be bad bearings in the ac compressor.
 
"sounds alot like a rod knock" "The noise does seem to come from the oilpan/tranny area."

Even though the A/C effects it, this could just be affecting the load on the engine, and the amount of vibration from a cracked flex plate, (mine was just replaced for the same sound) This is very to hard to diagnose. When mine was on the ground, it so sounded like something would come through the block.I tried to listen closer crawling under, but too much sound bouncing all around to pinpoint it. I even tried a long nut-driver jammed in to my ear (redneck stethoscope) applied directly to the access plate, and heard nothing. But I had the privelege of a friend with a lift. Standing directly under, while idling on the lift, the sound resonated from the flex plate access cover. It was obvious enough to schedule the job. We looked inside the access area first, and two Torque Convertor bolts were loose, but the plate was cracked. The area it cracks at is so far towards center, it's about impossible to see any evidence from the access area.
What about with A/C on, and slightly accelerating? It seemed any load on the engine that way would affect the noise and mostly quiet it down.
After about 500 miles, mine got worse and went away less and less. You can see why here:
http://farm1.static.flickr.com/238/524066199_24f10bc31f_b.jpg
Almost a complete circle.
I'll buy you a beer if I'm wrong on this guess.
 
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I had a timing chain making the same noise at an idle but as soon as you gave it gas, the noise would go away.
 
I've had much the same dilemma as you. Check that the exhaust crossover is not rattling against the bottom of the bellhousing, the rod that is connected to the pushbutton on your gearshift goes up the steering column to allow the key to be turned. It can rattle against the steering column and make sounds that are extremely hard to figure out. I've also had catalytic convertors that the brick came loose and rattled around sounding just like a rod knock.
 
I've always entertained the idea of a cracked flexplate...I just was hoping it was something else...hehe... I hate taking the tranny out. I wish the damn noise would just fail already so I knew what it was. Diagnosing a noise that isn't causing any other problems is a pain in the ass...

which if I can't pinpoint it this weekend is going to be the course of action I take... I just moved into the new house so I have to wait atleast 2wks before I put a damn car up on blocks... Good thing the neighbors how camaros...I'm guaranteed that they'll have their cars up on blocks more than I will!!!
 
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If I listened close, I remember even going over a set of railroad tracks at low rpm would very slightly alter the noise. This also is what leaned me away from possible internal engine noises. I dunno, with 176k, something in that area of my drivetrain has enough slop to tug slightly on the plate when bouncing maybe. Or maybe with no crack, the plate is supposed to absorb that small motion??
Why the hell do they call it a "flex" plate anyway?
Never asked that question or thought too hard about it.
 
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