My teenage daughter's '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

 

I think you got it right sounds like the flexplate very common problem.

 

Stang,

Thanks for the reply.

My Grand Cherokee is an early '93 4.0 4x4 Automatic.

How can I tell which transmission it has? AW4 or 42RE?

Thanks

Eddie

 

Shifter bezel will have both 1-2 as lowest position for an AW4. If it looks like this, it's a 42re.

 

x2 on the flexplate. not sure how the zj is set up, but you should be able to remove the inspection plate and check those bolts real easy.

 

Are the flexplates for the AW4 and 42RE interchangable?

 

Moved to GC tech.

OEM is for XJs.

 

It's best to get a flex plate from the same year and tranny as the Grand your taking it off of. The holes that the flex plate has can change from year, make, and equipment. If anything compare the two flex plates to make sure they match.

I had a knock in my cherokee, thought it was the flex plate, then my #3piston came apart (engine still started...lol). If the flex plate looks good and bolts are tight drop the oil pan (to bad you just changed the oil) and take a look up in the engine. A knock can also mean a broke wrist pin. Have you checked compression?