4.0 Engine Noise

[CloudmanXJ99]

1999 XJ stock with 161K miles. Owned since it was new.

Just had the exhaust manifold replaced so we can rule that one out but here's what's happening...

...when it's cold, under load (any acceleration) it has a 'clacking' sound. Like a diesel. After it warms up it goes away. However, once it's warmed up, it still has a very minor rapid clacking noise you can hear when you drive next to something solid like a cement barrier on the highway, but only on acceleration.

You cannot hear it during deceleration or at an idle (although tech who worked on it last said he noticed a very slight lifter noise).

From everything I've read it could be piston slap (though some have said that can't happen in a Jeep), injector noise, and of course lifter noise (but I don't think lifters make a 'clacking' noise do they?...it's more of a ticking sound right?).

Ultimately it has to go in to the garage to know for sure but thought I would get some input from you knowledgeable types. Kind of like to know what I'm talking about...so when the dealer tells me its a muffler bearing I can, with confidence, tell him he's nuts. 8)

TIA to anyone out there for your input.

 

[TerryMason]

Did you figure out what the problem was? I did some research from these and it ranged from lifters to exhaust to a transfer case chain.

 

[greg92jeepxj]

By the way you describe the clacking and diesel sound , it sounds like either spark knock or connecting rod bearing clearance issues . Piston slap is a real possibility since the Pistons need to expand to the cylinder bore when the engine is fully warm. Sometimes a cracked flex plate is mistaken for these faults.

 

[Bounty__Hunter]

Could be a busted piston skirt as well. Lots of possibilities. I wouldn't rule out exhaust leak just because it's been recently replaced.

 

[JPNinPA]

Sounds like exhaust leak from the heating up and nearly completely gone. With the engine off and cool pipe the exhaust of your shop vac up the vehicle exhaust and feel for leaks up by the engine.

Things happen like exhaust and intakes don't seat properly. The gasket move while being installed. Exhausts plates are warped. Bolts stretch or loosen.