PONCHO130

I think it be better to do an ls swap! I'd rather go through the trouble dropping it in than to deal with this crazy noise!

AstonishingXJ

Okay so I just checked the harmonic balancer nothing wrong with it, I started up the jeep and the knock is almost completely gone... Now it has a slight diesel sound, but I've heard that's common in these.

DFlintstone

If it sounds like mine post #13, it may last a while. It's made the same sound for something like 150K. 135 till 279....I did just pick up a little, "rat, tat tat" on start-up though.

Vincenza V

Mine sounds EXACTLY like post #13 too. Flex plate and bolts looked good when I checked them a year ago. I think I am going to live with it until it gets worse.

It only happens when cold, and just upon start up. Forgot what oil filter I have. 179K miles

C H E R O K E E 98XJ

Mine also does it until warmed up. What could that mean?

DFlintstone

I guess it means when it all goes "Ka-boom" allot of us want to know exactly what was it, anyway! Please post it up!

I have not ruled out crank end-play. Granted anything like that might maybe should have gotten worse by now. I suppose it could be checked at ether the crank pulley or even at the rear...Somebody can correct me, but I believe the 4.0 has only one main bearing that holds end play.

DFlintstone

Piston slap is one that goes away when it warms up. (the pistons get a little bigger). If mine did that I'd keep it away from women and children. (I mean always be nice to it before it wakes up a bit)

PocketsEmpty

Lol...dude, that is just how 4.0's roll. Seriously. Mine has the same sort of knock although maybe not as pronounced as in your video, but it runs AMAZING otherwise. I'm not even worried about it. I switched to synthetic Rotella T6 5w40 oil and it made a great difference in the smoothness of the engine, and quieted things down. Try it, otherwise, I think you might be chasing nothing. I would say you're wasting your time, but you're gaining valuable troubleshooting skills nonetheless. I think all 4.0's I've heard make this same exact sound to some degree.

cruiser54

Get one of these for about $10.

Blackcherokee290

Holy crap I FINALLY found a video of a knock that sounds like identical to mine!!!!!!!


Post#13 is freaking exactly like my jeeps knock. Tranny shop killed the flexplate idea. I'll check the HB but idk. AstonishingXJ - if you ever find out your problem please post it up dude. If I ever figure mine out I'll post to this thread as well.

CrawdadSlim

I'll let you in on a little secret. Most of the guys giving advice on your xjs noises have a few of their own.

cruiser54

This is way more effective than internet videos:

Blackcherokee290

Lol no kidding. I've got one of them and used it to try to track my noise down. Last time it came in handy was when PS pump started going out, that bearing was LOUD under the stethescope. Anyway I was just stoked I heard a youtube video of the same noise.

Blackcherokee290

Yah I'm getting that CrawdadSlim hahahahaha. I really haven't heard a quiet XJ engine come to think of it. I'll bow out of the thread so I don't hijack it anymore than I have.

DFlintstone

Problem? What problem? It was 32* and I had parked it fully hot shortly before. An Hr? . That and the mike on the camera really brought the sound out. (great for the video) Normally it's very muted, but clearly there. Maybe I should post up a "normal" knock.

I can envision a small bias on the main bearings causing the crank move just enough to make a noise, but hot enough to beat the thrust bearing to shreds. IDK!