Chrysler DRB & Knock?

Hey guys, two things here.. It's an 89 Cherokee Pioneer 4.0 231 Aw4 216k miles

First off, when the engine has fully warmed up (oil pressure around 20, temp gauge roughly 190-210) I get a relatively slow steady knock. It seems to get louder around the oil pan, but it's very difficult to tell. Actually now that I think about it, standing in front of the car it seems to come around the grille area. Anywho, it's only present at idle (650-700RPMs) and goes away whenever it leaves idle. But it's only there hot. Oil was recently changed by myself, and I didn't notice any odd particles.. The jeeps done this since I've had it (a little under a year) and it hasn't gotten any worse or better. Does it no matter the gear. My intial thought was prehaps the harmonic balancer, but the rubber around it looks just fine. Plus, when the balancer went bad on my 3300 GM v6, it didn't sound constant, it sounded like marbles in a coffee can that was being shaken.

Secondly, I've been reading through the Renix manual and I'd kind of like to get my hands on a Chrysler DRB. I looked through ebay and couldn't find one. Are these avaliable anywhere for sale? I know typically factory scan tools are outrageous, but as long as it's like under $200-300 I wouldn't mind since I intend to keep this awhile. I'd like to see if any KAM faults were stored, and see if I an't get real-time data on the sensors.

If you have an auto, check to make sure the flexplate hasn't cracked.

Early 4.0L engines are also known for "piston slap" - but I think that's more when cold than when warm.

Something else to think about - see if you can't drain off a quart from the bottom, then dump in a quart of straight 50 or 60 racing oil. This will keep the mix a little thicker when hot, and should help to rule out bearing noise (if it muffles the noise, it's a bearing.)

Good luck on the DRB-II. Some around here have managed to score some for reasonable prices (usually when I don't have any readies!) but know that the Snap-On MT2500 will also work, and there were more of them made. It will give you decent information as well.

youre also gonna need the jeep adapter to hook up the DRB2 to the Renix

I had really bad piston slap in the 90', it was there from day one when my dad bought it new. The dealer did little to own up to it and dad just drove it. It will run like that for a long time, untill he died in 02' and around 150k. I had the engine rebuilt and it runs smooth now, no knock!

JXPEEJ said:

youre also gonna need the jeep adapter to hook up the DRB2 to the Renix

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Or for the MT2500 - either should be easy enough to come by (especially the JEEP-1 adapter for the Snap-On.)