'96 Jeep 4.0 pinging: Seafoam as a remedy?

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Dec 13, 2006

I have a '96 Jeep Grand Cherokee with 148K on the clock. I bought it last year at 133K. It was clean as a whistle and appears to have been really well maintained. Overall, it runs like a top. However, I get spark knock climbing steep grades on the highway in warm weather (70F and above). I usually run 87 octane like it says in the book - except in warmer weather when I know it will ping if I do not use premium. The engine had a recent tune up by me (new plugs, wires, cap and rotor, air filter, cleaned CCV system and throttle body.) This didn't help the pinging.

As far as other parts go: the front oxygen sensor looks like it has been recently changed. All air intake tubing and vacuum lines are in great shape. Timing is not adjustable and this engine does not have an EGR valve and does not have a knock sensor. The cooling system is all new as well. The engine temp never goes above 200F either. No OBD codes show.

Would running a Seafoam treatment be a good idea to remove any carbon from the combustion chambers, or is there something else? I could just run higher octane all the time, but I feel that this engine should be able to run on 87 octane as designed from the factory. For what it is worth, my father-in-law's '96 Jeep 4.0 has the same problem. He drives a lot less than we do so it isn't much of an issue for him.

Thanks for any advice or experiences from Jeep owners out there.

Andrew S.
I'd run the Auto-RX clean up schedule. I had a 95 JGC 4.0 and it had a distributor with a Hall-effect module to control timing. I thought there was an adjustment. Have you check the timing with a light?
Hi Eddie:

I haven't checked the timing with a light; I just checked the factory service manual and unfortunately the distributor cannot be rotated to adjust the timing anyway. It actually has a forked alignment slot that keeps it from being moved once installed. It even says that altering the fork to rotate the distributor will still not affect timing as the PCM controls it.

Regarding Auto RX: How would adding that to the crankcase remove carbon from piston tops and combustion chambers? The engine looks really clean under the valve cover, it doesn't burn any oil and is quiet so I don't see what Auto RX would do in this case. Maybe I am missing something here (?)

Seafoam (or maybe a small stream of water down the intake or through a vacuum line while running) was my thought to possibly clean the combustion chambers followed by an oil change to eliminate the possibility of oil dilution. It is almost due anyhow (5K on MaxLife 10w30.)


Andrew S.
I get a bit of hesitation with my 4.0 when climbing grades or accelerating quickly (but not at WOT). I've been told the crank position sensor can cause this condition, but haven't tried replacing it yet. You might consider this.
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I would go by a can of actual combustion chamber cleaner.
I've never used seafoam but the GM and Mopar cleaners work very well if used properly.
Get the engine nice and hot and spray 3/4 of the can down the throttle body (fire it down the idle port too) while the engine is idling.
Shut off the engine and spray the last 1/4 can down the throttle and bump the starter to help distribute the remaining cleaner to all cylinders.
Now here the important part. Walk away...
let it soak for 6-8 hours or over night to soften and dissolve the carbon.
Then take out an drive it hard! lots of WOT 2nd gear accell and decell. Get the engine nice and hot again.
Be prepared for lots of white smoke.
If it still pings I'd consider a professional injector power flush.
I haven't had very good results with the add to tank injector cleaners.
Rotating the distributer won't effect ignition timing at all. Timing is referenced off the crank sensor
Seafoam = seemed to relieve knock
Amsoil PI - good injector/valve cleaner
Gumout Regane - yellow=clear bottle.
Rabber X2 I followed the instructions on a can of Seafoam carbon cleaner and did a hotsoak. It helped a 275kmile engine pass NOx spec on the original cat.
Maybe the exhaust is getting plugged a bit - a cat can get partially restricted and the cylinder head will be hotter than it should - Welcome to Knock City..
Also, there may be a service bulletin about a reflash of the computer.
Thanks for the advice everyone!

The cat and exhaust was new when I bought the vehicle at 133K so I doubt that is the problem. The spark plugs are the correct heat range as well. I think I may try the combustion chamber cleaner next.

mechtech2: You made a good point about reflashing the computer. I searched the Web and Chrysler did issue a TSB about this where their dealer scan tool can retard the total timing advance for this exact purpose. If cleaning the combustion chambers doesn't help I will look into that.


Andrew S.
Reflash as mechtech2 says and I'd also score a can of Amsoil Power Foam and some PI or regane. Power Foam has done wonders for many vehicles for me and seems to pull more crud out than the seafoam through the break line. Good luck man because 4.0 aren't meant to be fed a diet of anything other than good ol' cheap regular!
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