My teenage daughter's beat up old '93 Jeep Grand Cherokee (300K) developed a lower engine knock/rattle. We pulled the accessory belt and the noise was still present. We thought is was probably timing chain rattle/slap. Yesterday I replaced the timing chain/gears (while I was there the water pump and radiator hoses were also replaced along with an oil change). Nothing other than black oil was found in the pan.

Upon startup the noise is still there. The noise goes away as engine speed is increased in nuetral. The noise is reduced when the automatic transmission in gear at idle (forward or reverse). The noise is the same regardless of engine temperature.

Does anyone have any ideas?

I am thinking it may possibly be a cracked flexplate. I am going to pull the inspection cover and check for loose bolts ASAP.

Thanks in advance!

Cheers

Eddie

All of my 4.0 Grand Cherokees have rattled my 96, and my 2002. I think its the heat shied or the catalytic converter, I have learned to ignore it even though it is annoying

My Cat did that also on a 1996! I am at 250k and still going!

I have heard that the oil pumps will eventualy fail so keep an eye on your oil pressure!!

Thanks for the replies.

It is defnitely coming from the lower engine/trans area. I think the noise was partially masked by the timing chain rattle (there was lots of play in the old chain and the teeth on the crank sproket were getting "pointed").

Cheers,

Eddie

I worked on a lot of cherokees in Kuait when I was in the air force I I changed quite a few harmonic balancers. The rubber would start to seperate that holds the two sections of metal together and it would start as a rattle. It would then, if not changed, start eating the drive belt.

My 4.0 rattles like a diesel sometimes, always at idle. Thought it was a chain myself, so I ignore it. 247K on mine.

hows the oil pressure?
oil pump starting to fail?
300k is a long time for a pump.

Consider putting in motor medic or 20w50 oil to see if the noise quiets down.

Rich

Oil pressure is 40psi at idle, 60psi at 1200rpm and above.

The harmonic balancer was changed 3K ago.

I will pull the inspection cover ASAP. I might even unbolt the torque converter to get a better look. It would be nice to have a borescope!


It's probably not a good idea to start the engine with the torque converter unbolted???? It would be like a very, very light flywheel.

Thanks

Eddie

Pull one plug at a time and eliminate a rod knock?

I thought a rod knock usually gets louder at higher RPM and loading.

I have blown rod bearings on a couple of engines and that was always the case.

Thanks for the input.

Cheers,

Eddie

My '93 4.0 187K always sounded like a diesel but one annoying rattle I found and replaced was the belt tensioner.

My '02 4.0 181K sounds like a diesel too.