Here is some information that came from another web site that has been very informative and helpful, hope it helps.
Problems with Engine Ping
Contributed by drbob
The Symptoms
I have 96K miles. For sometime now the truck will begin pinging very heavily. I changed gas from Mobil to Shell and that helped but at times, for no reason, it just goes crazy.
The pinging may stop on its own as fast as it started. Other times the fact that I shut it off and restarted it later the pinging would be completely gone.
Dealer says carbon build up. I don't buy it, wouldn't the pinging be more consistent?
Info from Ford via Don Krumm
I too had the same problem and Ford Technical Service Hotline helped me solve it through a friend at an area dealership. It involves removing cylinder #5's spark plug and observing it for carbon buildup. This buildup is due to a lower intake leak of engine oil from a faulty gasket. Ford has an updated gasket that is made of sheet steel with rubber vulcanized around the port openings. This is much better than the original cardboard gasket. Hope this answers a lot of questions to this problem.
Dr. Bob's Solutions
Two possible solutions:
First, force a new profile into the engine management system. To do this remove the battery leads for a little bit to erase the old stored profile. Now's a good time to clean those terminals anyway. Now store a new profile by driving the car a bit briskly in situations where the car has been pinging before. It should learn the new profile. Do this with a new tank of the gas you would prefer to run. That would be regular, I'd bet.
Second solution is a bit more drastic and expensive in the long run. Your car has an "octane shorting block" that can be removed to retard the ignition timing by about 3 degrees. Upside is that the pinging will almost assuredly be eliminated. Downside is that performance and economy will suffer if you do this. Since these are marginally acceptable at best, save this as your "last resort" solution.
The octane shorting block is located under the hood, in a harness just to the rear of the fuse box. So if you are standing at the right front corner of the car with the hood open, move to the rear a bit to the fuse box. Now, look at the rear of that fuse box for a big bundle of wires that goes toward the firewall and somewhat down towards the engine. It's about 1 inch or so in diameter, wrapped in plastic tape. About 4 or 5 inches back on this bundle, from the fuse box, locate a pair of wires that come out and are folded back against the bundle. These are maybe 4 inches long, and go to a plastic socket that's maybe 1.25 inches wide, taped back on the bundle (at least on my car.) In that socket is a rectangular plug, maybe 3/8 inch thick. This is the octane shorting block. Remove it and store it in the glove box. Pinging, gas mileage and performance are all gone now.
Try the reprogramming solution first. Do it with a new tank of regular gas, so it learns with the gas you use, in conditions you typically drive in. Maybe a half-hour of driving will do it for you. Use the shorting-block trick only if you can afford the poor mileage.
Also:
Inspect the spark plugs. New plugs are cheap. If you see any oil or coolant deposits on the center electrode and insulator, you may have a cracked head or bad head gasket. '91 and '92 cars have a known problem with both. Oil or coolant in the chamber will cause pinging. Of course, the oil and/or coolant levels would be other clues to this problem.
Contributed by Murray Hartman
I had a pinging problem in my Explorer but fixed it easily. After doing a compression check and finding good compression but crusty deposits on spark plug #5, I did the following and my pinging and oil consumption disappeared. I regapped the spark plugs (they were too narrow) then retorqued the lower intake manifold bolts (a few were a little loose). I have driven 2000 km without any oil consumption (before I would have had to replace one liter of oil in 1500 km). I recommend everyone to retorque their lower intake manifold bolts once a year or when the engine starts to use oil (without visible leaks or blue smoke). Retorquing the manifold is an easy solution before resorting to replacing the manifold gasket!
Contributed by Ray Aakjar
If all else fails, check the Baro reading on the MAF sensor.(key on, engine off). It should be 159hz @ sea level. If it's off, it could cause a lean condition, causing a ping. I've seen about 10 of them do that.
Cleaning the MAF from Brian Johnson
You might also try cleaning the MAF. Here are some nice photos and the procedure for a 1994 Explorer.
Since my Explorer had started pinging very much, and resetting the computer by disconnecting the battery trick did not work, I decided to clean the Mass Air Flow (MAF) Sensor. The sensor is located next to the air filter housing on the left side of the engine compartment.
Removal of the sensor takes a special T-20 screwdriver (Torx-20). These screws have a protrusion in the middle, preventing your screwdriver from inserting fully. I removed one screw with needle-nose pliers, and the other screw I hammered the protrusion down with a nail punch. Not really recommended, but I did not have a torx screwdriver with a hole in the center.
Here is what the mass air flow sensor from a 4.0L engine in a 1994 Ford Explorer looks like.
