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

[Jonathan Stiver]

Weird. I’ve had several of these 4.0’s, never heard anything like that. My initial instinct was top-end too but after reading over everything you’ve done… I’m not so sure anymore. Your next steps would be mine too. I wish I had better insight but good luck and keep us posted!

[Jonathan Stiver]

For what it’s worth I run 10W-40 in these motors but the weather is very warm here, most summer afternoons are 90-105*F.

[Robbie]

I’m planning on using some 40 weight diesel engine oil next oil change… if it makes it to the next oil change. I’ve read these engine love 40 weight, and I’d like to have the extra goodies floating around. The only reason I’m waiting till the next oil change is to let the MMO have a real chance to clear something out.

One possibility with the oil sender weirdness. It was rather warm those two or three days that the noise was quieter. Down in South Carolina… averaging 30F – 40F these days. Friday, Saturday, and Sunday were nice and warm, around 70F.

I’m pretty much a noob at this. So far I’ve been going off of the Haynes manual and what I’ve seen on various forums and youtube videos. I just don’t have the $$$ to take it somewhere.

[Jonathan Stiver]

Hah, who am I to tell you about the heat, I’m north of the border in Raleigh but my Grand Cherokee occasionally sees sub-zero temperatures in the mountains. I change the oil every spring & fall (was about to this weekend) to use a different weight for summer/winter. Some thicker weight oil can only help but there still is something going on there.

[Robbie]

I’ve got so many possibilities floating around in my head from lurking on repair forums.

Piston skirt, flexplate, lifters, power steering pump, wristpin, rod bearing, blah blah blah

At this point I’m trying to find the most likely troubleshooting path. On top of $$$ being limited, my time is as well. I only have a few hours each weekend, and then whatever time off from work I’m willing to sacrifice.

[Jonathan Stiver]

There may not be much you can do until it finally “breaks” if it’s going to. It’s interesting that it seems to be oil related though. Btw I noticed you mentioned 4 qts + 1 qt. My manual says 6.0 qts for the 4.0L with the standard filter.

[Robbie]

Six quarts makes the dipstick read high.

[Jonathan Stiver]

I know, it often times does on these, sometimes it takes a while for the filter to completely fill. Just something to keep in mind. I end up doing about 5.5 qts and adding .5-1.0 qt in between changes. Even if it was a tad low that alone wouldn’t cause that noise anyways, just thought I’d mention that…

[Robbie]

You know… I just realized something. I’ve been driving it to work, very short trips. Maybe three miles one way. It’s shifting pretty rough. I wonder if it’s the flexplate. Hopefully the Haynes manual will tell me where the flip it is.

[Robbie]

Pulled the transmission fluid dipstick last night… it’s brown. I wonder how possible it is that I’m an idiot and this is a transmission issue and not an engine issue.

[Robbie]

God! Now I’m reading stuff about the camshaft position sensor. That should be easy enough to check though. Just put a stethoscope or screwdriver on it.

I’ll do that and a compression check over the weekend.

[Robbie]

Finally found some time for a compression test. All the numbers look good.

Cylinder #, Dry #, Wet #

1, 172, 179
2, 173, 181
3, 171, 176
4, 170, 176
5, 173, 178
6, 173, 178

Here is the video: /watch?v=2hI588Scr60

Another video of the noise: /watch?v=VIfaJOzVjV8

Next step is to pull the oil pan.

[Robbie]

So, wow. With my limited time and tools it took me weeks to get the dang exhaust pipe off and out of the way so I could get to the oil pan.

Got the oil pan off today and found three pieces of piston skirt. After a visual inspection of the bottom end… looks like piston number four is the culprit.

I’m gonna see if I can get away with just replacing the piston. With the age and mileage of the motor, it’s either replace the piston or replace the motor. I’d rather see if I can get a few thousand more miles out of this thing than replace it right now.

[college man]

keep us posted on your progress. 😉

[Darren]

I’ve had 4 of these engines in the last few years come to me with a very similar noise, 3 times it was a cracked piston skirt. I tried to attach a picture, but it won’t work for some reason :huh:

[Author]

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