Hello all....I'm new to the forum so handle me easy.
I just purchased a 2000 Cherokee Sport with IL 6 4.0. It has 85000 miles and has some sort of unusual noise in the engine compartment. It sounds as though it's coming from the front of the engine.... most of the time you have to listen close to hear it and at times it's more noticeable, but never really loud. It's hard to describe....doesn't sound like a lifter....the peck is not that keen. It's a little dull peck/knock that goes away when you increase the throttle the slightest bit. I've been a mechanic (Farm Tractors/light construction machines) for 25 yrs. and should be able to handle the solution once I know where to start. It sounds a little like a piston pin, but I'm hoping it turns out to be something else. A friend of mine who swears by Cherokees says his makes the same noise only maybe a little worse than mine.....he said not to worry unless it stopped making the noise....not sure I can live with that. Is this a common occurance with this particular engine? Anyway, if anyone can give me some suggestions, it would surely be appreciated. Thanks in advance.
Love my Jeep! Jwilly2

 

You sure it's not the sound of the injectors firing, it's quite loud on some cars...

 

Having worked on diesel engines most of my life, I really wouldn't know what sound I'm listening for if it was (as you suggest) the injectors firing. Could it just be one by itself or would it be more likely they would all be doing it. If it's the latter, I don't think it would be the injectors firing because it's just a tick....tick....tick, not a tick,tick,tick and again, it's a dull tick not a keen/sharp tick. What do you think? Thanks

 

I'd grab the old long screwdriver, and start giving a listen to things under the hood then. The only other thing I can think of that makes a really audible tick is when my elec. fan kicks on...

 

lol i had this on my xj. one way you cantell is if you slam the throttle wide open, it should make the noise. If it's two knocks it is a rod bearing or wrist pin. One knock and it is loose torque converter bolts. this is sctually fairly common on the straight sixes i was told, just from design. to tighten them all that is needed is to remove the dust cover on your transmission and tighten to torque specs. make sure it is centered

 

Sounds like the traditional 4.0 cam/lifter peck !
I have had two that done it, there is a write up in the florida jeepers forum about it. The cam lobe/lobes will get a flat spot on them and at low idle, low oil pressure the lifter does not take up the slack until you get above an idle an the oil pressure picks up ! and it will get worse as time wears on to where the lifter will no longer take up the slack, and it will start to develop an ever so slight miss.
The write up talks of using a oldsmobile/ pontiac push rod that is a little longer to take up the slop versus doing a cam lifter job/ in other words its a band aid !
The jeep I am selling /trading had the same issue and I chose instead of all the labor and money of cam, lifter, push rods to just go on with a new engine and be done with all the issues of a high mile engine, labor,
money ,
time.
But the longer push rod/rods will do the job for a cheap fix.
Go to http://www.floridajeepers.net/portal.php which is the forum and do a search on the stickeys
hope this helps, trust me you are not the first to have the mystery peck/knock

 

Guys....thanks for all the advise! Guess I will take my friends advise and not worry about it unless it stops making the noise This is my first Jeep and I absolutely love it!