JerseyRodder

I recently got a free 1997 Grand Cherokee. Its only problem is a loud knocking that sounds like it's coming from the #5 cylinder. It quiets down at about 1700 rpm. It was parked as soon as it started to make noise. It is a 4x4 automatic with a 4.0 210,000 on the motor. Trans and transfer case were fairly recently rebuilt (about 20,000 miles ago). I thought it would be a rod bearing but oil pressure is perfect. It seems to drive and idle decent. I only drove it around the block though. I pulled the plug wires one by one while it was running and the knocking wasn’t affected. Don’t you usually see a drop in oil pressure with a worn bearing? Doesn’t stopping the cylinder from firing usually quiet a rod knock? I did a forum search and saw a lot of people had issues with the flex plate either being cracked or loose. I haven’t checked it yet. Could it be a lifter, valve spring? Something else? I’m going to do a compression test this weekend. What else should I check? Thanks for your input. ---Rich

the stig

i have a 2000 grand 4.0 with just over 120k on it and i to had a loud knock in my engine...and alot of what you are saying sounds like mine, it would quiet down around 1500-2000rpms, the oil pressure was perfect and it drove perfect. my problem (and what sounds like yours too) was a rod knock. i replaced the engine about 3 weeks ago. if yours is as loud as mine and it sounds like it is then i would do the same. the price isnt too bad to do this plus you get a 150,000mi parts and labor warr. if you get it from where i got mine. if you need to or choose to replace it and have ? let me know and i will try and help either way good luck

stinkypete85

If it sounds like a rod knock it most likely IS a rod knock. Pulling a plug wire will not necessarily make it stop. The crank is still spinning inside of that worn bearing and whos to say its not 2-6 bad bearings? Also oil pressure will not always drop depending on the cause of the bad bearing. If you only drove it around the block the oil pressure wouldn't even have time to drop in some cases. You may be able to get away with new bearing and a pump if your lucky. The only way to tell is to pull the engine and inspect. Been there done that.