sv41878

OK so my 96 Cherokee with a 4.0 makes a spitting noise when under load. I thought it was the exhaust cuz that's what it sound like and where it sounds like its coming from. But it's not, at least that I can find, I don't feel a leak from the header to exhaust connection like I thought I would. It does not burn or leak oil, doesn't go through coolant, doesn't go through tranny fluid, and doesn't lack power. Anyone have suggestions as to where and what to look at next?

jusolbob

I don't hear so well anymore, but the sound you describe sounds to me like a timing issue. Possibly one or more cylinders firing just a tad too early, and spitting back through a still partially open intake valve.
I assume you have checked for any loose plugs, right? Or maybe I didn't hear the same "spitting sound" you did. Past experience tells me that if I hear "spitting" I have an ignition problem, or more specifically the timing of that ignition. That's a tough one. If it was easy there would be a dozen answers already. Let us know what you find. Good luck.
Bob

sv41878

Only problem with that theory, which was also a guess of mine, is that the timing in a 96 with a 4.0 is not adjustable. Everything runs through the Crank position sensor and the ECU. I would think that it would throw a code if this were the issue. As for plugs and all, I thought that might be the issue, checked them all for any irregularities (i.e. funny burning, over ignition, etc) and found nothing, plugs look good. Any other ideas?

jusolbob

"Any other ideas?" Yeah, well, maybe.
I had an old Ford P/U that had the same symptom you describe. Bottom line was that the ECU was on it's way to the trash. It was erratic in when it fired the plugs. But again, it's tough when you're the only one that can hear what you describe. Is there a specific temperature or condition when this spitting occurs, or is it just random?

sv41878

It's pretty well constant, began only when it was cold, would warm up and go away. The plugs were out 3 days ago and didn't show any misfire, oil, burns, etc. Looked pretty clean for 6000 or so miles on them. Everything I found points to exhaust but I've been through it a few times. Only place I haven't thoroughly checked is exhaust manifold which is what I'm looking at next.

jusolbob

"began only when it was cold, would warm up and go away"

That sounds like the beginning of an exhaust leak, but as you already know they get progressively worse. I just went through that with my CJ. Tiny little pin hole in one flange of the manifold gasket. What a PITA they are! I'd be interested to learn what you find.

sv41878

Thats what I'm hoping, haven't been through the exhaust gasket since when I first heard it. Hoping that is all it is and since I'm in NY, I'm saying that lightly cuz here EVERYTHING rusts, gonna be a PITA to get those bolts loose.

wwxjwheeler

The idea that the timing is not adjustable on a 4.0 is a misnomer. It may be necessary to "reset" the timing once in a while to compensate for an aging engine. There is actually an old jeep tech way to do it that involves TDC and and cutting up an old distro cap. This was of course not necessary on 4.0 with distributor-less ignition systems.

With that out of the way it sounds to me like an intake manifold leak. When cold there is a gap between the metals (steel block and aluminum intake). Once warm the metal expands to fill the gap. On some vehicles this is accompanied by a high RPM whistle.

Hope this helps

Willys55

Add that to my list of "now I heard it all"

wwxjwheeler

Although I have never done it to my XJ I was told as such by an Chrysler/Jeep/Eagle service tech. This probably has to do with the timing chain stretching over time and hence being a few degrees off. I adjust the ("non adjustable") timing on my 88 5.0 mustang as I see fit with no issue. You just have to remember that there is an ignition advance curve programmed into your EEC. The mustang has a shunt that can be removed so you can set the "static timing" without interference from the EEC

I dont see why the jeep would be any different.

captainwoot

You can file the "ears" of a dist and adjust it to a point, the timing is controlled by the pcm, but with a chrysler scan tool there is a section that says "set sync signal" with a range of -8 to + 8 degrees , the idea is to set it to zero.
I think by what you are describing, it sounds like the beginings of a cracked exhaust manifold, assuming that it goes away when hot. Or the beginings of a cyl misfire that the pcm hasn't "seen" yet to thow a code.
good luck!