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Ticking/tapping 4.0L engine

8

89Daytona

NAXJA Forum User
Location
NY
I have a 98 XJ with 148000 miles that makes a ticking noise almost all of the time. It ticks when cold and when warmed up, while driving if I let off of the gas the ticking almost goes away (its almost not noticable). There are also certain rpm points while driving where the ticking seems to disappear. Here is a video of the noise. Could this be a cracked exhaust manifold, or is it likely a valve or bearing problem?

Edit: The ticking just started last week, I changed the oil yesterday and the noise didn't change at all. I also tried disconnecting the sparkplug wires one at a time, and there were no noticable changes when I disconnected each wire then reconnected it.
 
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Almost sounds like your fan is hitting the fan shroud when the engine "torques". This might explain why it goes away when you let off the throttle because the torque goes down. Or some other moving part in the front of the motor is hitting something.

I'd check your motor mounts before doing anything else. If those are fine check the tightness of all your pulley bolts/fan bolts.

Your 4.0 shouldn't be dying yet unless it was abused by a previous owner or something.
 
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Sounded like the bottom end to me, but I can't tell from the video. Didn't sound like a valve tap. I'd check the easy stuff first like the others said, and go from there.
 
One of mine (87 Renix with 279999 almost time for a birthday) Has sounded like that for the last 50 or so thousand miles. I agree with everyone else tho check the easy stuff first. Mine is definitly rod bearings (but it will be a stroker this winter) so I just baby it along untill I get time to do it. Also mine has never gotten any worse. But it does go away a little if I let off the gas. I have heard of 4.0s running a long time with a little piston slap could that be it?
 
Well today on my way back from work finding the problem (or atleast one) got easier, the engine started making really bad knocking sound and running really rough. So I got a tow back to my place and took a look at the oil dipstick and noticed that it was twice as full as it should be and the oil is a milky color... and the coolant was low. So it looks like its time for a headgasket change.
 
So I finally got the engine apart.... It has two bent pushrods on cylinder 5, the intake valve is stuck open, the piston is shattered (I'm guessing the piston hit the valve), there is some deep scoring on the cylinder walls (possibly where the coolant leaked into the cylinder). Its amazing the engine was still able to run with all that destruction. I guess Jasper will be getting some business from me...

pics coming soon
 
the piston probably didn't hit the valve because these motors are not "interference" motors.....likely that the coolant in your cylinder caused it to hydrolock,but it had to be one mother of a leak!!!
 
The engine might have turned into an interference engine if the piston got sloppy on the connecting rod... or maybe broke loose from it.
 
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