I could really use some help trying to figure this problem out. I have 98 with just over 115k miles. for the last few months ive been noticing a faint knocking sound coming from around the fire wall, usually went at a stop light or parked. this sound starts after its been driven for a few miles. It seems like theres a slight drag on the motor and recently the oil pressure seems to be lower then it usually is, after its warm about 10psi driving is just under 40 when its a cold start it idles at 37 driving is 50, last i checked thats normal? however i just took it a tranny mech and he said hes never heard of a flex plate cracking on Cherokees and that could not be it. Now im stuck trying to figure this thing out before it gets worse. any thoughts or suggestions would be awesome.

 

rocker knock?

 

Your mech is mistaken, the flex plates do crack. The only way to know for cretain is to pull the tranny and torque convertor since the cracks are typically between the bolt holes.


More importantly, the change in oil pressure would cause me to to look at both halves of the rod and main bearings as well as the cam bearings.

 

If you're seeing a drop in oil pressure, it would probably be either a main or rod bearing issue.

What I would try is this: put some Motor Honey in it and see if your oil pressure comes back up and the knocking noise decreases. If so, pull the oil pan and check out the rod caps and main bearing caps in the vicinity of the knock. You'll be able to tell which is the culprit from an abnormal wear pattern on the bearing...

The rest of the repair would depend on how bad the bearing and surfaces are worn.

 

Are you reading the oil pressure off of the dash or with a guage? normal idle oil pressure is about 9-12psi, although i have 2 cherokees that like to idle no less than 30psi... My 2001 cherokee idles at about 10psi.

All of my jeeps have a light knock, as do all jeeps ive ever heard. It is hard to get the noise that you are talking about, but it sounds like what mine do.

newer jeeps no longer have knock sensors and they do lean out alot when idling which can cause a light "knock".

However, It is extremely common on almost any year cherokee for the flex plate bolts to come loose. you can check this by pulling the inspection cover off and checking torque.

Hope that helped, may want to find another jeeper and try to diagnose noise together.

 

thanks guys im hoping its not any thing to do with a rod or the crank.Im in college right now so its rather hard to get down into the gritty work. luckily i found a local mechanic who deals only with jeeps. Ill throw in your guys' suggestions and see what comes up. thanks again

 

im incollege too man i know how yya feel! i only have simple have tools with me like wrenches and ratchets and other little stuff...i usually just work on it in the big parkin lot haha everybody walks by and looks at me but i dont care haha