New noise, fishing for ideas

I've got a 96 with the 4.0 and AW4. I've developed a knocking noise while idling and out of gear. When I shift into drive or reverse the noise goes away. My first thoughts are to check the flex plate and exhaust. Y'all have any more thoughts?

RR3

This may sound crazy but if you own an XJ, anything concerning annoying noise location is possible. My exhaust manifold was cracked and the leaking exhaust sound like the motor was knocking at an idle. When I would put it in gear it would stop. A new manifold confirmed the noise was the leak.

Just a thought..........................

That sounds exactly like the flex plate on the Montana-mobile (the XJ I refurbished for the ex-GF in Montana). Incredible knock at idle, and the noise when away when it was put in gear.

The flex plate had an annular (circular) crack right at the perimeter of that steel ring that the crankshafts bolts go through. The crack ran almost 2/3 of the way around, and it's a wonder to me that it didn't fail completely.

You should be able to see it if you remove the inspection cover at the bottom of the bell housing and pry on the flex plate with a long pry bar. Use a bright light, though, because it isn't easy to see.

Looks like it's loose flex plate bolts. Hard to tell if that's all it is right now. I couldn't get the inspection plate off due to the bolt at the corner near the exhaust down pipe being in backwards. I can't remove the bolt without unbolting the exhaust pipe. I've got class tonight, so I'll tackle those rusty bolts tomorrow.

Eagle, can you check for cracks in the fles plate without removing the bolts to the torque converter?

Thanks,
RR3

Whew! It was only loose bolts. I pried on the flexplate from all sides and no cracks visible. Thanks once again to the great information shared on this forum, I got right to the cause of the problem and fixed it with with minimal trouble.

Thanks to all who directly or indirectly helped. :worship:

RR3