Basic info: 91 cherokee, 4.0 HO, 4,5" 31s.

So I jump on the highway yesterday and shes running great at 70-75. I get to my destination and all is well. I head home...all is well. Go to the gas station later. all is well. This morning I jump in to go to work and she starts right up. Backs out of the drive way and i put it in drive....not so well. The jeep is knocking something vicious! Only does it in drive.

Any ideas of what it could be? Flexplate maybe? IDK PLEASE HELP!!

 

How's your oil pressure?

Flexplate is a possibility for sure.

 

Honestly I have no idea. I have an oil pressure gauge....just haven't hooked it up yet...SMH

 

If it only does it in drive, I'd pull that bellhousing inspection cover off and check those flexplate bolts. And the goofy stuff like your fan hitting the shroud due to weak motor mounts...

 

Also check to see if your exhaust is anywhere near the crossmember

 

Just curious, what weight oil/additives are you using? I have a '93 with a 4.0, bought from an older man who didn't drive it except to the store and soon afterward it started knocking something fierce; I tried using a combo of 20w-50(2) and 4 10w-30 plus STP thinking it was a knocking rod. This only made it worse. I was desperate so just as an experiment I drained it out and used the factory called for 10w-30 only. Drove the thing on the highway and slowly but surely the knock eventually went away. I believe (my pro mechanic agreed) that my lifters were probably sticking from the sludge and crust on the lifters due to the short drives the previous owner did and was probably causing the valves to hit the piston tops. The problem slowly went away and now it runs like a champ. Hope this helps.

 

so its been awhile since i posted this but the problem has been fixed. turns out my flex plate was fine. the problem was that only the two top bolts on bell housing were tight and the engine and tranny were slapping against each other..tightened the others up and BOOM, problem fixed. i took advantage of the down time and went a little nuts. I went ahead and clocked my t-case, did a one link shifter on it, borla exhaust i scored from the pick-n-pull for $30, welded my 8.25, disk brake swap, relocated my axle side shock mounts on the rear, shaved the bottom lip on the 8.25, new shocks all around, sway bar discos, chevy brake lines up front, relocated gas tank to the inside via hole in floor, removable doors, stripped interior, on-board air using ac and scored a set of tsl/sx and rims for $180. SHES A WHOLE NEW BEAST NOW!! thanks everyone for your inputs!!!