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Brad, Jeep Dealership Tech
Category: Jeep
Satisfied Customers: 6712
Experience:  19 Yrs Chrysler/Dodge/Jeep. ASE Master (L-1) Certified
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Cherokee: I have a knock on my 99 4.0 that I can not identify.

Customer Question

I have a knock on my 99 4.0 that I can not identify. It doesn't follow the "guidelines" of any one particular thing, ex: piston slap. flexplate,wrist pin, etc. I have a video of the noise but my I can not identify it,neither could my mechanic. Any help would be appreciated.
Submitted: 5 months ago.
Category: Jeep
Expert:  Brad replied 5 months ago.
Good morning and welcome to JustAnswer!!My name is ***** ***** I have worked for a Chrysler-Dodge-Jeep dealership for 18 years and I will do my best to help. I work part-time here on JustAnswer to help you and other repair their own vehicles, and I get credited by your ratings.. So before leaving the site make sure and leave me a rating. You can still reply to me as many times as needed, even after the rating.. I will need for you to be my hands and eyes since I'm not there, and to be honest with today's electronics a scantool may very well be needed to retrieve the codes or to monitor data to see what's going on... Do you have the video uploaded so I can listen to it? Is it misfiring or running fine? Have you tried disconnecting each cylinder to see if the noise goes away to pinpoint which cylinder it on?
Customer: replied 5 months ago.
first video of the noise.
Customer: replied 5 months ago.
more pronounced
Customer: replied 5 months ago.
This has been driving me nuts for about a year. Hasn't gotten much worse. It's mainly only at the 1500 rpm range with a few very light knocks occasionally at idle. No codes but may have a little sputter at that rpm. I was convinced I narrowed it down to flexplate with a stethoscope however it could just be bouncing noise around. Compression seemed the same in a wet and dry test. No power loss. Only 68k on the motor. Once it gets really hot after about 30 minutes of driving the noise almost completely goes away. It then turns into more like an exhaust noise.It doesn't knock but almost does a little sputter like an exhaust manifold leak.
Customer: replied 5 months ago.
No visible cracks on the flexplate but I know sometimes they crack around the center and you need to drop the tranny to see.Plugs,cap,rotor, wires all changed. Banged on the cat but did not hear a rattle. Disconnected fuel injector one by one. Knock may get quieter when #6 is removed but not positive.
Expert:  Brad replied 5 months ago.
I watched both videos and it doesn't sound good.. Have you drained the oil thru a paint strainer to see if you have any metal in the oil?
Customer: replied 5 months ago.
No.I've done about 3 oil changes. No flakes but I haven't dropped the pan. Piston skirt you think?
Expert:  Brad replied 5 months ago.
I had one years ago that sounded something like this that we couldn't narrow down and we added a qt of Marvel Mystery oil and after a 20 miles test drive the rod come out the block so we got a new engine.. Not to sound negative but it doesn't sound good and I'm surprised it's lasted a year sounding like this.. What is the oil psi staying at? It's not a constant knock so it's difficult to locate but when it's the loudest and you disconnect #6 injector and the noise quietens I would suspect a wrist pin, bearing. Unfortunatly this will require a tear down to carefully inspect the engine to determine the source of the noise.. If it were a valvetrain issue it should have become a misfire if a lifter was to blame so I would drain the oil thru a paint strainer and if you see any metal I would tear it down..
Customer: replied 5 months ago.
I ran marvel through it for about 1500 miles. No affect on it. I've probably only driven it about 3000 miles in the past year.Oil pressure is fine at about 50-55,35-40 hot idle. I guess I was looking for more things to check but it sounds like you won't be able to be of much help unfortunately to get me any further than I was already at.

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