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Discussion Starter #1 (Edited)
I'm lost-is this a lifter noise? piston skirt?

2002 WJ, 4.0, 122,000 mi., last Sunday it went from having the usual amount of lifter noise to having a very loud tapping sound, all the time when the engine is running, with a metallice sound to it under acceleration around 2000RPM. I added a bottle of Marvel Mystery Oil, and a day later added half a bottle of Seafoam to the crankcase and fed the other half down the throttle body. no help. I decided I had a lifter collapse on me. but, it runs as well as it ever has. Yesterday I pulled the V.C. All pushrods tight, all spitting the same amount of oil, all rotating, none seem to be bent. dropped the belt to eliminate the A.C. , power steering pump, water pump. Still there. I used a wrench, screwdriver, and a stick as a poor man's stethoscope, and cannot determine for sure where this sound is coming from. narrowed it down to 2nd cylinder. if you're under the Jeep, is loud there, on top, it is loud there. no exhaust leak. I just changed the oil and checked the torque converter bolts. can anyone suggest what to look at next? It doesn't sound like a rod knock or piston slap. broken skirt, maybe?
 

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Discussion Starter #2
still unknown

OK, I spent half an hour last night with a mechanic's stethoscope listening to the engine. there doesn't seem to be a place anywhere on the engine where the sound is coming from. It pretty much sounds the same everywhere I listened. no particular place where the tapping sounded any louder. A lot of other noises though, the area around the front main makes a heck of a lot of whirring sound. I even went out and tossed that damn cat out from under the hood of the ZJ and listened to the 4.0 in that one. Someone replaced the engine and trans in the ZJ before I bought it in April, so I listened to it to know what a 4.0 is supposed to sound like. the noises in the WJ engine, except for the tapping, all sound the same. in fact, the tapping sounds pretty close to the slight lifter tap in the ZJ, just an incredible amount louder. I guess I will be pulling the head Monday and see what I can find. I am supposed to be driving the WJ 1000 miles in a couple weeks, so it's kind of important to get it fixed. I'm back to guessing it is a lifter, even though no problem showed up under the valve cover.
 

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I have a 95 and 01 with 4.0L the 95 ZJ has 245,000 and the valve train chatters and makes noise like a diesel or a "tappet" sound. If you have a bottom end " Nock" it could be a ristpen or piston skirt. Take it to 6000 rpm's that will let you know! If it is still running I would drive it across country! Its a JEEP .........Good Luck
 

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Discussion Starter #5
I haven't checked the EVAP, but unless one of Santa's elves is in there making horseshoes, I don't think it is the cause. This is one of those noises you can hear across the parking lot. I've had it up to 4000 RPM, and it's still going. If it was my Jeep, I'd leave it alone awhile, keep driving, and see what happens. But this is the one the wife drives and she doesn't like the noise. she's also not happy about those heated seats not keeping her backside warm any more. I'll get to those some year.

I will be opening up the engine Monday, unless Delta drops me somewhere between Ohio and Arkansas this weekend (who gets married the weekend before Christmas?). I'll let everyone know what I find.
 

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Discussion Starter #7
Wouldn't there be some drop in piston slap sound when the fuel injector wire is pulled? I pulled each, one at a time, and heard no change in sound. I also have moved up from 5W30 to 10W40 on the oil, probably not enough viscosity change to notice on the sound level.
 

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Hi, new member here.

I have experienced the same on both my XJ 4,0 and YJ 4.0, the problem was a stuck lifter. On the older 4.0, the head have to be removed in order to replace the lifters, so I replaced all 12 lifters when the head was off.

Here is a pic of the stuck lifter, you can see the lifter is not returning to the top. There will be a gap between the pushrod and the rocker arm causing the loud tapping sound.

 

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Discussion Starter #9
4.0, r.i.p.

well, this morning I was printing off a couple pages out of the manual to help dig into the 4.0, when my wife came down the stairs ready to go to town. I didn't know she had to go somewhere. I should have let her drive my ZJ, but she put over 140 miles on the WJ over the weekend, I didn't figure a few more would hurt too much. wrong. she got about a mile from the house. she said the engine started to rattle, she lost power, and then she lost her steering. I managed to get it started once, it rattled and banged and then jammed up and stopped. It is stuck where the starter won't turn it over now. I rolled it down the hill backwards, around the corner, and about halfway home, then towed it with the ZJ to the bottom of the drive. the inch or so of snow we had last night is trying to melt, and our drive has a steep portion right off the road. it's slippery enough the ZJ wouldn't pull it up. I went and got the Ferguson tractor, it won't hardly climb the slippery drive by itself, much less with the WJ chained to it,so the busted Jeep will stay down on the road awhile. I think that the tapping was a busted piston skirt, and it finally finished grenading. I guess that is one Jeep that won't be headed to Kansas for Christmas.
 

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Discussion Starter #10
shrapnel

finally got a chance to get the pan off. Number 2 piston scattered all over the place in there, with one piece almost the size of an egg wedged against the cam. I can see the rod is bent also, and there is some damage to at least the edges of the cam lobes for #2.

so it's time to pull the engine. I wish that AMC Gremlin was still sitting in my dad's back pasture, I spent 50 bucks for that car to use the engine in the old CJ while I rebuilt that one back several years ago. my dad finally cleaned out his shed and hauled off the engine. too bad, I really could use the crank out of it and build this busted engine into a stroker.

anyway, a summation for possibly someone's benefit: this engine went 400 miles after it started tapping; the tapping didn't go away when warm or when the injector wire was pulled; the tapping sounded more like a lifter than anything else, but I couldn't pinpoint the source; and certainly, the tap goes away once the pieces all let go, leaving you with.....the silence.
 

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Discussion Starter #11
after finally geting the head off this engine, I found a piece of a piston ring about a quarter inch long in cylinder number 1. small aluminum flakes in cylinder 3 and 4. how do pieces of piston number 2 get into 3 other cylinders?
 
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