My ZJ is my baby... never gives me any trouble, but the other day my engine kinda sputtered on startup (warm) but i shut it off and she cranked right back up fine.

NOW (the next morning & noon) when i start her she fires up just fine... but then there is this hollow wooden knocking noise that taps every 10 sec for about a minute.

It SOUNDS as if its coming from the transmission/cat/exaust area???

I don't think that the engine sputter is at all related because after the tap stops everything is back to normal. (and it's not in the engine)

[[[I HAVE BEEN EXPERIMENTING WITH MY EXAUST ALOT LATELY]]]

Right now im running a straight pipe, and it is NOT the source of the noise!

Any ideas???

Thanks guys...

-Nate

(1997 ZJ 4.0 L6)

 

Take the serp belt off and see if the noise goes away. Put the cat converter back on.

 

Engines need back pressure to run, by running straight pipes you have gotten rid of most of it. Try to put the cat back on and drive it for a week and see if you are still having the problem.

 

I didn't remove my cat, its cat/cherry bomb/turndown under the cab.

anything you can think of running that setup now?

AND do you guys have a clue why the motor stutered on that ONE startup?

normal every once in a while?

 

/\ would mean no cat or muffler.

As far as the hollow knocking noise, is it a backfire sound like a gun shot, or more like a rod knocking on the side of the block?

Have you heard it while outside of the vehicle or only while in the driver's seat?

 

its not true, my bad for not specifying.

no not at all its a small tap (very faint)

 

Have you checked the oil level lately?

When is the last time the fuel filter was changed that could be the problem causing the sputtering.

Or could be that you have a lot of build up on your spark plugs that arent letting it spark correctly.

Not enough info to thoroughly answer your question.

 

It could be something as simple as the pipes expanding as they warm up.

 

Engines do make some noise when they're running.