1994 Cherokee XJ 4.0L
This one has me stumped. Any input is appreciated.
Been running like a top for a while. The motor at least. Lately, after sitting a week or so it would run rough when started. Then it would clear up after a few seconds. It doesn't get driven much.
I let it warm up the other day and drive it pretty hard. A few wide open throttle runs up to about 40mph. Parked it. Next day went to start it and it ran rough. Shaking violently. No CEL. Cleared up a little and now is rough all the time. Was leaking fuel from the FPR, so, I replaced it. Didn't fix the problem.
So, I warmed the motor up about halfway and pulled the plugs. Hooked up my leakdown tester and checked for losses. Test showed about 6%-11% loss. Pretty good I think for the age. I could hear air coming from the oil filler cap in all cases. Not much in intake or exhaust and nothing in radiator that I could tell. Results posted for this.
So, after I was done I decided to do a compression test to see what was going on as well. 150psi on all cylinders but #2. That cylinder had no pressure. Maybe 20psi. Repeated text and got same results. Repeated leakdown and got similar results. Hard to tell compression stroke this time (wasn't pushing much air out) so I checked TDC of both exhaust and compression stroke. Couldn't tell which was which, but, results were either 6% or 15%. Both leaked into valve cover.
So, how does leakdown pass but compression failed so bad? Any ideas? Problem doesn't appear to be spark, fuel, or vacuum. I'm guessing a problem in the head? Maybe a blown out piston? But, leak down doesn't seem to verify this.
This one has me stumped. Any input is appreciated.
Been running like a top for a while. The motor at least. Lately, after sitting a week or so it would run rough when started. Then it would clear up after a few seconds. It doesn't get driven much.
I let it warm up the other day and drive it pretty hard. A few wide open throttle runs up to about 40mph. Parked it. Next day went to start it and it ran rough. Shaking violently. No CEL. Cleared up a little and now is rough all the time. Was leaking fuel from the FPR, so, I replaced it. Didn't fix the problem.
So, I warmed the motor up about halfway and pulled the plugs. Hooked up my leakdown tester and checked for losses. Test showed about 6%-11% loss. Pretty good I think for the age. I could hear air coming from the oil filler cap in all cases. Not much in intake or exhaust and nothing in radiator that I could tell. Results posted for this.
So, after I was done I decided to do a compression test to see what was going on as well. 150psi on all cylinders but #2. That cylinder had no pressure. Maybe 20psi. Repeated text and got same results. Repeated leakdown and got similar results. Hard to tell compression stroke this time (wasn't pushing much air out) so I checked TDC of both exhaust and compression stroke. Couldn't tell which was which, but, results were either 6% or 15%. Both leaked into valve cover.
So, how does leakdown pass but compression failed so bad? Any ideas? Problem doesn't appear to be spark, fuel, or vacuum. I'm guessing a problem in the head? Maybe a blown out piston? But, leak down doesn't seem to verify this.
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