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View Full Version : 4.0 Detonating



Hurricane 4x4
08-12-2004, 10:25 PM
I have a 1996 zj 4.0 with about 156K miles. The engine has had the pinging problem for a long time now... probably 30,000 miles. For example, when i am going up a hill at about 60mph or so, and the jeep shifts down into 3rd to keep the speed up, and the rpm's go somewhere in the range of 3000, I will hear bad pinging sounds (they make me cringe) coming from the engine. I am sure it is pinging, because it goes away when i use premium gas. I have new plugs, wires, cap, rotor, replaced the fuel filter about 5,000 miles ago, good airfilter, cleaned throttle body recently. And today I tried using a can of mopar combustion chamber cleaner to no avail.

After I replaced all these parts the 4.0 runs great... smooth idle and good response. however the sucker will still ping unless I use premium gas. The price difference between premium and regular is 20 cents, and I hate band-aid fixes anyway.

Any ideas?

(btw, nice site!)

Jeeps And More
08-17-2004, 01:25 AM
use a fuel system cleaner such as amsoil PI or BG 44K (the amsoil is avalable on my website)

over time engines build cokeing on the back of the valves as fuel runs past these deposits they rob it of octane. also if the deposits are in the combustion chamber they may form "hot spots" which may lead to detonation (pinging) try one tank of premium gas with the treatment in it chemicals take time then after you have burned the whole tank try mid grade or regular to see if the problem is solved.