jon1998

I know I should, but honestly don’t remember what I got, but it was factory spec. I’ll throw some champions in if it continues to make noise, plugs are easy enough to change. I took it out this morning and did some hard acceleration and it didn’t make the noise, I’m thinking maybe it just needed a session or two of hard driving, usually I baby this thing. I’ll still keep an ear out for it, especially during the next hot day. Thanks everyone for all the suggestions and help, I really appreciate it.

I checked out some of the videos and posts on dieseling, my noise is a lot more sporadic than what I saw. Its also only got 45k miles so I can’t imagine the pushrods are worn like that. I’ve got the day off so might just drop it off at the mechanic today and see what they say, I don’t want to risk causing any permanent damage. Funny enough my 89 comanche made that exact same pushrod noise, it drove me nuts, I never knew what it was until now

I put some seafoam in it and zero smoke, it still seems to make the noise. Its a light tapping knocking, kind of like if you were to lug it near stalling. I’ll look around for some heat sheilds like Hornbrod said, it definitely seems to do it worse in hot conditions but perhaps this is some other noise like accessories or who knows. The gas I run in it should be good, its chevron, but I’ll try a different gas station just to rule out bad fuel. It accelerates smooth and drives great other than that noise

Thanks for the replies, I’m already running a fourth can of seafoam through the tank but I think another can this time through the intake is worth a shot, I’ll also look around for that heat shield too.

My 99 Cherokee 4.0 5spd makes a noise that makes me think of predetonation, when driving in a hot environment I hear the marbles in a coffee can knocking when I accelerate aggressively. It revs smooth and builds power, but the pinging spontaneously appears. It used to be way worse when I got it, but three cans of seafoam in the tank and some premium gas really helped it. I have also replaced the plugs (gapped correctly) and wires, and it runs at 210 degrees. I checked fuel pressure and vacuum and both checked out fine. Any ideas on what it could be? Are these jeeps sensitive to 87 octane or something? I’m really starting to run out of patience for these 4.0s By the way, love the forum, it has by far the most helpful jeep knowledge

I sold my Comanche, but picked up a 40k mile 1999 XJ in its place. It has the ax15 and I changed the trans fluid when I first got it since I was worried about factory GL5 fluid eating up the brass synchros. I put 10w30 synthetic in it, since that seemed to be the best choice at the time, but now I'm starting to worry I made the wrong choice, I called a local Jeep specialist and they said they wouldn't recommend it. Its also getting a little hot outside, I live in FL, and I'm worried about the oil getting too thin. What do you guys use in your XJs/MJs with the ax15?

I'll check the flexplate again this weekend, sounds like thats what it has to be. Thanks again for the help everyone!

It is an automatic, but I did check the flex plate bolts for tightness already and they all seemed fine. I didn't see any cracks either, but are these cracks small enough to be easily missed? How likely is this horrible noise rod knock? Thanks so much for the replies

My 4.0 has developed a knocking sound emanating from the oil pan area, it is very faint at start up and much louder when the jeep is warmed up. It seems to only be present at idle, but when I put it in drive I can hear the knocks slow as the rpm drops. Despite the knock, the jeep has really good oil pressure and runs really good. I pulled the spark plug wires from each cylinder to see if taking the load off would reveal the one with the bad connecting rod bearing, but the noise never went away, suggesting the problem may not be in the connecting rods. I also pulled out all of the pushrods and inspected them for bends; they all looked straight. None of the rocker arms had play in them so I guess the lifters were good. I have also checked the flex plate for cracks and loose bolts and didn't find anything. What could his knock be? Do these engines just make this noise naturally, I have been told rod knock is common to 4.0s, though I haven't personally heard one make a noise like this.

The clicking sounds speradic, but also too rythmic to be shrinking metal. It also clicks regardless of whether the engine was shut off warm or cold. Thanks for the idea about pulling the spark plug, I will try that. The exhaust manifold will click and shrink no matter how long the engine runs. It heats up within only a few seconds and can sound somewhat rhythmic when shrinking. The fuel injectors will for sure be a rhythm though. I'm with Cruiser that it's probably just the exhaust manifold making the noise but it's worth a look into the injectors just in case. I have had issues similar to yours with my 98 XJ not starting after it had run. It was so inconsistent when it happened though so idk what finally fixed it. I know that some sensors like the cps can be affected by heat. It's possible that heat soak is causing a sensor to act up after you run it. The heat soak issue is pretty frustrating since it runs great otherwise . I'll go to the store and 20 min later it will have trouble starting, misfire, shake, and idle real low until it starts driving again. I haven't checked the CPS yet, I'll try that too.

The clicking sounds speradic, but also too rythmic to be shrinking metal. It also clicks regardless of whether the engine was shut off warm or cold. Thanks for the idea about pulling the spark plug, I will try that.

After the vehicle is completely turned off, I can hear clicking eminating from the engine. I put a screw driver to the individual injectors and my ear to the screwdriver, using it like a stethoscope, and I could hear the injectors make a clicking sound. This is with the vehicle completely off. Do you guys have any ideas as to what may be causing this to happen? The Jeep is also hard to start after being warmed up. I'm wondering if the injectors are flooding it.

Are these diodes vehicle specific? Also, where on the back of the compressor does the ground wire go?

Hey everyone, I have another question about the wiring to the ac compressor on my 89 Eliminator. The ground wire on the compressor is cut and I am not sure whwre to ground it. I have heard it is grounded on the back of the compressor itself, but I do not know what exactly to attach it to. I have also looked at a wiring diagram and noticed that this wire is supposed to go to a diode. Do I need a diode? Thanks everybody for being so helpful, this club has been great for learning how to work on my jeep.

Thanks for clarifying that for me, a picture would be really helpful