1992 4.0

[Bob]

My 1992 4.0 sounds like a diesel when ideling. I have taken it to 3 differant mechanics and none could give come up with the cause. I have tried all the snake oil additaves and oil weights, has no effect. Any idea what is causing the above. Thx Bob

[Blupupher]

How does it run otherwise and how many miles. Any oil useage/ burning?

[Bob]

How does it run otherwise and how many miles. Any oil useage/ burning? It rums great, no oil burn. Just at idle, when warm ,sounds like a diesel. At first listen you might think lifters but I been told it not the lifters. About all I can do to elimanite it is turn up the radio.
130K miles.....

[Blupupher]

Well, I can't think of anything off hand. Maybe pull the valve cover off and see what that looks like.

[mlyle88yj]

Sounds to me like your rod bearings are going out. what is your oil pressure at idle? When Running down the road?
Or you could have a cracked exhaust manifold? Depending on where the noise is coming from. Let me know

[Bob]

Sounds to me like your rod bearings are going out. what is your oil pressure at idle? When Running down the road?
Or you could have a cracked exhaust manifold? Depending on where the noise is coming from. Let me know
With 10/30 oil the pressure backs off a little at idle but is fine when running down the road. with 20/50 the pressure is good all the time. I have tried the miracle cures, stp & lucas additavies does not have any effect. also it does not do it for the first minute when started cold. Unable to pin-point exactly where the noise is comming from even with a listing tool.

[mlyle88yj]

Well that rules out the cracked manifold. All I can figure is your rod bearings are going bad. The only thing you can do is change them or wait for them to go out completely which could lead to other problems down the road.

[jeff mclain]

I ve personally had 2 4.0 jeeps and once the miles add up they sound like a diesel at any thing below 1000rpm definately a upper end noise I feel that its probally rocker arms/lifter noise ive had one 4.0 with 250,000miles and always noisy at idle. Ive even put rod bearings and timingchain in one with 100,000miles and no change in noise. If your noise were rod brg it would get worse fairly fast and would probally change with different weight oils and additives. personally I wouldnt worry much about it Ive seen 4.0s go many miles rattling and never give problems just turn up the cd player

[zazlo]

The noise you are hearing is a slight piston slap ,it doesnt seem to effect the life of the engine.Ive done a few while they were still under waranty.Dont worry about it & keep your oil clean,Its the best thing you can do for the life of your engine.