Margaret Jr., my 2001 Cherokee 4.0, is making more than the usual noises. It's a pretty loud knocking. (Old Margaret was driven daily with 308K on her when I sold her, and I think I heard all the "normal" noises.) It started a day ago, when I was 350 miles from home, and aside from the noise, I noticed no other issues, and the trip was otherwise uneventful. Oil pressure did not drop, and no loss of power. It's much louder than lifter tapping, but I don't *think* it's a rod going. It doesn't matter if the engine is warm or cold. It gets louder and faster as RPMs increase, but does seem to drop off at very high RPM. When you let off the gas, it even very briefly seems to disappear, but only for a split second. I pulled the inspection cover and looked at the flexplate, and the 4 bolts I could get to are tight, and I didn't see any cracks, though I know looking at it this way only tells half the story. I pulled the plug on each fuel injector one at a time, and it made no difference that I could tell. I pulled the valve cover, and nothing is loose, and it doesn't appear to have any collapsed lifters. I briefly ran it with the cover off, and all rockers, to my untrained eye, looked OK. My questions are these: 1. In searching the forum here, I see a loose timing chain mentioned as possible cause of a knocking noise. Any thoughts on that as that fitting with what I've got here? 2. Regarding a bad rod- is disabling a single cylinder at a time a definitive way of ruling out/confirming rod noise? 3. It is a very regular knock; would a cracked flexplate have a regular knock, or would it be a bit more...'random'?


Thanks for any input, and I'd love to hear any other suggestions appropriate for a driveway mechanic with basic tools.

 

When you change the oil, look for aluminum dust/pieces of piston skirt.

 

Pieces of skirt, that's what you can expect when you call your car a "she"....