Greetings: 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.