I have a 2004 grand cherokee with the 4.0. 182,xxx miles. I just recently bought it cheap. It has a noise that’s something between a knock and a tap. The oil was super dirty. I changed it and at first test thought the noise was gone but then it came back. I’ve pulled the valve cover and everything is tight. Today I pulled the oil pan and all the rods were tight and no metal in the pan. I’ve noticed that as it warms up the sound quiets some and if I rev it up and release the paddle quickly the sound is more pronounced, almost as if something is loose and spinning out. Any ideas? Timing chain?

 

How is the oil pressure?

Any chance of a video with decent audio?

 

Oil pressure looks good.

Ill try to get a quality recording.

 

Try the Grand Cherokee section. This is the Cherokee section. Two different vehicles.

Also, get a mechanic's stethoscope.

 

 

That's a pretty pronounced noise. It may be a collapsed lifter.

 

Is there a conclusive way to diagnose a collapsed lifter?

 

The good news is, yes, there is.

The bad news is, you have to pull the head!

But before you do that, inspect your flex plate. It's probably the lifter, but it might be the flex plate, and inspecting it is free, and not difficult.

 

If it was coming from the flex plate, would the sound subside significantly when the motor warms up, as is the case with my issue?

 

Cracked flex plate typically only makes noise at idle or under real light load once under a load up high rpms they typically can’t be detected . You have what sounds like a collapsed lifter. Hopefully it hasn’t done more damage to the engine by being ran long without being repaired . I hope you have a back up vehicle .

 

With a collapsed lifter, would a rocker arm be loose?

 

A stuck lifter will easily bend a pushrod causing “loose” rocker arms it can also wipe out the cam causing no more lift of the pushrod and no movement of the rocker . Not all scenarios are the same or similar with valvetrain failure .

 

I only suggest the flex plate because it is POSSIBLE (but not likely) and easy to check. Do the easy & cheap stuff first.





Hmm. Not sure, but it would certainly affect your power. Does the engine feel sluggish?


I think you may be able to pull the valve cover and see a difference in how the rockers behave.

 

IMO this is most likely piston slap. The GC's seem to be more prone my theory is they hit higher rpms with the 42RE. The tell is that it goes away once warmed up completely. Mine has had it 5 years now. Oh I changed the chain, hoping that was it. Then did the lifters and valve job. Nope. Still there. May get around to pulling the pistons sometime. Oh if your lifters aren't broke, dont fix them unless you know how to dial in the preload on the non adjustable valves, you will be in for a wakeup call if you don't.