CommanderXJ

Ever since I've had the jeep. I've had this ongoing pinging under acceleration. It occurs only when under load and its most prominent at about 3000 rpm. The weird thing is. Is that there is no pinging if I run 91 octane. But with gas prices being the way they are nowadays I switched back to 87 octane and the noise is back.

I have tuned this car up within the last 2 yrs. This includes spark plugs and wires, fuel filter, distributor cap and rotor. I even dumped seafoam into the intake manifold thinking it might have been carbon build up but it barely pooted out any smoke.

Does anyone have any ideas as to what is causing this?

Cherokee 4.0

djb383

May need to pull the head and clean piston tops and combustion chambers.

tjwalker

I agree with djb383; this is likely a carbon problem. Using Seafoam is no guarantee of resolving a carbon issue.

The first thing I do when I suspect carbon is to switch to a tank of higher octane to see if that resolves it or at least makes it better. And you have already confirmed that it does for your XJ.

You could try another product like GM or Chrysler or Ford top end cleaner and see if you have any better results. If not, pulling the head is not a bad idea

CommanderXJ

Is it at all possible that it could be a cracked exhaust manifold? Engine only has 138k miles.

tjwalker

Not likely. Increasing octane and having the pinging stops points directly to carbon.

If this were mine, I would stop by the Jeep dealer and pick up a bottle of Chrysler Top End Cleaner. That's not the real name, but they'll know what you mean. Probably about $10. Follow the directions and see if it helps. I have had some pretty good luck with that stuff before for moderate carbon. If it is severe carbon buildup, this will not help.

944.0

Looks like it is called mopar combustion chamber cleaner.

tjwalker

Yup, that's the stuff......thanks.

Personally I think that MCCC is hands down the best choice for aggressive carbon cleaning. It is introduced in a "foam", which also expands when inside of your engine. So the way the chemical is introduced and distributed is more effective than Seafoam.

I believe that Chrysler, GM and Ford all have the same chemical formulation in their top end cleaner products, so I wouldn't hesitate to buy it from any of these dealerships so if your Jeep dealer is out of it, stop by the GM or Ford parts department; my experience is that some parts departments can be out of it at times.

I have had darn good luck with it, and highly recommend it as symptoms demand. Be sure to FOLLOW THE DIRECTIONS ON THE CAN!

cruiser54

Yep. Either that or a can of BG44K in the gas tank.

CommanderXJ

Hm....phooey lol. I should have mentioned previously that I started noticing this problem back when I changed my valve cover gasket when I first got the car. At first I think I might have screwed something up (I was new to fixing cars at the time) or perhaps one of the lifters was getting stuck.

Just never made much sense to me when people kept telling me it should run just fine on 87 octane. I don't notice a hit in performance or mpg regardless of which octane I go with. I usually average about 16-18 mpg in the city.

I'll give the combustion cleaners one last shot and do it a bit more aggressively this time and see if that helps with anything.

CommanderXJ

Looks like that was the problem. I poured a can of seafoam into the throttle body and let it sit for about 7 minutes before I fired it up again, and it put on quite a smoke show.

Drove the crap out of it around the back roads and still heard the pinging. After about 10 minutes I really drove it hard and eventually the engine no longer pinged and the smoke cleared out.

I think it just needed to breathe a little.

rrich

Make sure your plugs are the ones called out on the underhood label, make, number, gap etc Often parts houses give or suggest the wrong ones.

Bosch in particular is a killer! Hilter's Revenge!