Jeep 4.0 i6 engine noise

[Robbie]

Hey everybody! I’ve been lurking a while, but this is my first post.

I’ve got a engine noise on my 2002 Grand Cherokee straight six 4.0. Vehicle has around 130,000 miles on it. Here’s the noise:

*EDIT
Since I can’t get the insert video thing to work and the youtube URL won’t show up… here’s the end of the youtube URL: /watch?v=IvG2Yze0JvQ

I have yet to figure it out. Was hoping somebody might have some insight. Here’s what I’ve tried so far (obviously with no success):

• Round of Seafoam
• Oil change (10w30)
• Checked the torque on the rockers
• Visual inspection of rockers, pushrods, and valve springs

I also ran it with one cylinder disabled at a time. The noise never changed or went away. I did this by unplugging each cylinder’s fuel injector electrical connection. I would’ve just unplugged each spark plug one at a time, but this thing doesn’t have a distributor… it has one of those plug rails. No way to unplug one at a time.

The noise first manifested about two months ago, immediately after an oil change. I bought the Jeep from my father-in-law and he told me he always put 10w30 synthetic blend in it. So, that’s what I put in it. Oil change + 4 hour road trip = engine noise. Perhaps the oil change was just a coincidence.

After the Seafoam and then subsequent oil change I did not find any metal pieces in the old oil. All the pushrods appear to be straight, and they all push up and rotate. All the rocker bolts were to spec torque (21 ft lb). Doesn’t appear to be any warping or cracking on any of the rockers. I can’t see any cracks in the top of the cylinder head. The noise definitely seems to be coming from something up top… in the valve train. At first I thought it was a bad/sticky/collapsed lifter, now I’m not so sure. After I got the valve cover off I figured that I would be able to find the bad lifter by pushing down on the pushrods. Whichever pushrod was “squishy” would be where the bad lifter was. All of the pushrods are solid. Any other tests I can do for the lifters without pulling the head?

I did replace the oil sender. The oil pressure gauge was maxing out and staying maxed whenever the vehicle was running. Never fluctuated. Replacing the oil sender fixed the pressure gauge weirdness. Something odd happened then. The first time I cranked it after replacing the oil sender the noise got MUCH quieter after about 30 seconds. It did that for a few days, now it’s just as loud as it ever was.

Currently the Jeep has four quarts of 10w30 synthetic blend with a quart of Marvel Mystery Oil.

Stuff I plan on checking out:

• Compression check on all the cylinders
• Pull the oil pan and check for a broken piston skirt
• See if I can feel around the bottom end while the oil pan is off.

Thoughts?

Topic

[Robbie]

New pistons, main rod bearings, wrist pins, and a valve job. Runs great now. No more little hammers in my motor.

Glad I replaced all six pistons, #1 and #6 were showing signs of beginning to come apart. Hairline cracks and such.

[college man]

Glad it worked out.Thanks for the update.

[Author]

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