96 XJ Engine Knock Help
07-06-2017, 04:19 PM
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Year: 1996
Model: Cherokee
Engine: 4.0
96 XJ Engine Knock Help
I am new to the forum and new to Jeeps in general. I have a 1996 XJ with 162k miles on it that has developed an engine knock and could use some help/guidance with trying to figure out the problem. I am fairly mechanically inclined and do all my own work on my vehicles. I have only owned the Jeep for about a month. Here is everything I know. Some of it may or may not be relevant but I figured I would include as much as possible.
Here is a video of the engine running.
I had the jeep loaded with people and camping gear and had been driving on the highway for 80ish miles when it seemed like I was losing some power and having trouble maintaining speed. I only have idiot lights, no temp or oil pressure gauges, but I do have an OBDII scanner so I checked the temp and it was up around 240F but the overheat light did not come on. It was at this point that I noticed a knocking sound and pulled over right away.
I started checking all my fluids and noticed that there were small metal shavings on the engine oil dipstick so decided not to drive at all and had somebody come trailer the Jeep back home. Weekend camping plans were ruined.
I drained the oil and ran a magnet through it and came back with a lot of super fine metal shavings. The oil also had a shiny copper color to it that kinda swirled around when dragging the magnet through it. I filled it up with new oil and ran it a bit in my garage trying to determine the source of the knock. When I drained the new oil it also had that shiny copper color.
I ran it without the serpentine belt to make sure the noise wasn't coming from any of the accessories or water pump.
I checked the flex plate bolts and they were all tight and no visible cracks.
I pulled each spark plug wire individually and there was no noticeable change in the knocking noise.
I pulled all the spark plugs and they all look like they are in good condition.
Using a stethoscope is sounds like the noise is loudest at the rear of the engine and at the bottom but it is really hard to tell.
I removed the valve cover and everything under it looks fine although once I get into engine internals I don't have a lot of experience diagnosing problems.
I dropped the oil pan hoping to find an obvious problem like chunks of piston skirt (not that I wanted broken pistons but I wanted an easy diagnosis) but all I found was some metal shavings a bit bigger than grains of rice but super thin. Some of the shavings are magnetic and some are not. The previous owner had a shop replace the oil pan less than 2,000 miles ago so I am assuming that all metal shavings are pretty new. He told me he had it replaced because the drain plug threads were stripped.
I'm not really sure where to go from here. If anybody has suggestions on what should be checked I would love some help.
I have no maintenance records but I bought the XJ from the second owner who purchased it in 2000 with only 20k miles on it. I got the impression it was very well maintained. It was never taken off road before I bought it.
I believe there is a vacuum leak somewhere based on the fact that when under heavy load the AC switches to only blowing out the windshield defroster vents.
I'm currently super bummed because I have loved driving this thing for the month that I had it and have big plans for it. Other than this knock it is in excellent condition mechanically and cosmetically.
Here is a video of the engine running.
I had the jeep loaded with people and camping gear and had been driving on the highway for 80ish miles when it seemed like I was losing some power and having trouble maintaining speed. I only have idiot lights, no temp or oil pressure gauges, but I do have an OBDII scanner so I checked the temp and it was up around 240F but the overheat light did not come on. It was at this point that I noticed a knocking sound and pulled over right away.
I started checking all my fluids and noticed that there were small metal shavings on the engine oil dipstick so decided not to drive at all and had somebody come trailer the Jeep back home. Weekend camping plans were ruined.
I drained the oil and ran a magnet through it and came back with a lot of super fine metal shavings. The oil also had a shiny copper color to it that kinda swirled around when dragging the magnet through it. I filled it up with new oil and ran it a bit in my garage trying to determine the source of the knock. When I drained the new oil it also had that shiny copper color.
I ran it without the serpentine belt to make sure the noise wasn't coming from any of the accessories or water pump.
I checked the flex plate bolts and they were all tight and no visible cracks.
I pulled each spark plug wire individually and there was no noticeable change in the knocking noise.
I pulled all the spark plugs and they all look like they are in good condition.
Using a stethoscope is sounds like the noise is loudest at the rear of the engine and at the bottom but it is really hard to tell.
I removed the valve cover and everything under it looks fine although once I get into engine internals I don't have a lot of experience diagnosing problems.
I dropped the oil pan hoping to find an obvious problem like chunks of piston skirt (not that I wanted broken pistons but I wanted an easy diagnosis) but all I found was some metal shavings a bit bigger than grains of rice but super thin. Some of the shavings are magnetic and some are not. The previous owner had a shop replace the oil pan less than 2,000 miles ago so I am assuming that all metal shavings are pretty new. He told me he had it replaced because the drain plug threads were stripped.
I'm not really sure where to go from here. If anybody has suggestions on what should be checked I would love some help.
I have no maintenance records but I bought the XJ from the second owner who purchased it in 2000 with only 20k miles on it. I got the impression it was very well maintained. It was never taken off road before I bought it.
I believe there is a vacuum leak somewhere based on the fact that when under heavy load the AC switches to only blowing out the windshield defroster vents.
I'm currently super bummed because I have loved driving this thing for the month that I had it and have big plans for it. Other than this knock it is in excellent condition mechanically and cosmetically.
07-07-2017, 09:58 PM
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Year: 1996
Model: Cherokee
Engine: 4.0
Found the problem. Cylinder #4 rod bearing is shot. Now to figure out if I can just replace the bearings or if I need to pull the crankshaft and have it machined.
07-08-2017, 06:30 AM
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Year: 1996
Model: Cherokee
Engine: I6 Cyl / 4L
Did you do a compression test?
Very rare that those bearings go for no reason. Usually something happens to make them go bad. You have to try to find what went bad.
With the dummy cluster lights, you could have been overheating and not known if the light bulb was bad. Which could crack the head or blow the head gasket.
Might be cheaper and faster to find another engine and swap that in. Fixing and rebuilding these engines is done (there are many threads on it) but it takes time, tools and patience. Sorry.
Very rare that those bearings go for no reason. Usually something happens to make them go bad. You have to try to find what went bad.
With the dummy cluster lights, you could have been overheating and not known if the light bulb was bad. Which could crack the head or blow the head gasket.
Might be cheaper and faster to find another engine and swap that in. Fixing and rebuilding these engines is done (there are many threads on it) but it takes time, tools and patience. Sorry.