PJ_Hunter

I have a 99 Cherokee with the 4.0 motor. I have noticed that in the last week or so I have a "knocking" sound at the rear of the motor, but only when the vehicle has been driven and the motor is hot. It doesn't knock when cold or restarting.

Example: yesterday it was knocking after arriving home after work (30 miles drive) and I turned it off and went inside to grab some water, drop off the mail and bla bla bla. 5 minutes, if that went by and then I headed to the DR. It didn't knock when I restarted it.

Can I please get some opinions on this please?

Thank you.

TechMike

Is it a knock that increases / decreases with engine RPM's or is it intermittent? Is the knock metallic in sound or more hollow? Auto or 5-speed trans?

PJ_Hunter

Kinda a dull metallic hollow knock, it does increase with RPMs. I have an auto tranny.

I hope to heck it isn't what I think. I can't afford to pull and rebuild the motor.

Cherockee

Cracked flexplate?

razor02097

how is the oil pressure?

jimmy21669

A hairline crack in the exhaust exhaust manifold will provide the same symptom....especially once the Jeep is warmed up. When it cools down, the metal contracts, closing the crack, heats up and opens.

I have had this, and it is a common XJ problem.

mcguyver_xj

sounds like the xh. mani. or flexplate

PJ_Hunter

OK. How does one check this and if there is a crack, how do I fix it?

PJ_Hunter

Seems ok. I need a new oil pressure sensor but just haven't done it yet.

jimmy21669

You have to REALLY look for it....one way is to put a colored "smoke" through the intake and plug the exhaust for a second to check for leaks....

Another is feel....use your hand (Carefully)

Another is with a mechanic's stethoscope.....

PJ_Hunter

If there is a crack, how is it repaired?

PJ_Hunter

What is a flexplate and where is it?

jimmy21669

Either weld it, or buy a new one. If you go the new one route, don't go OEM, just get an APN Header...just a few extra dollars.

PJ_Hunter

I am assuming that it is cast? Can I just hit it with a MIG welder, and run a bead along the crack.

I'll have to check when I get home. As for the colored smoke thing, any suggestions? I live in an area where you just can't go out and buy something easily.

excess650

The exhaust manifold on my '96 isn't cast. It looks like a steel tube header. If yours is the same, it should be weldable.

As for sourcing things, the 'net is your friend. Order it online and have it delivered.