98 Mustang GT Pinging 5/15/13

My Mustang GT pings when accelerating up a grade of at least 3 degrees, beyond 40MPH. The pinging is reduced when I burn premium fuel, but it nevertheless still pings. I cannot drive beyond 50MPH over mountainous roads due to loud pinging which I am afraid will damage the engine. I have replaced the O2 sensors which were generating codes. No mechanic whom I have approached can tell me definitively how to eliminate the pinging. Otherwise, the engine, with its 144,00 milers runs perfectly. Help!

I am guessing that the timing on a '98 Mustang is not adjustable, but if it is, there is the possibility that the timing is too far advanced.

A more likely scenario is that the EGR valve needs to be cleaned or replaced.
A frequent cause of pinging in an otherwise-healthy engine is an EGR valve that is gunked-up.

If the EGR proves to be okay, then you might want to have the health of the cooling system (especially the thermostat) evaluated.

Standard or automatic? Can you set timing on this engine? If you can’t, the only answer I can think of is an aftermarket programable ignition ( look in Hot Rod magazine.) Baring that, you will have to keep the rpms up by selecting lower gears.

Check the EGR passages for clogging, not just the valve.
Change the thermostat if it’s over 5 years old.

Has this car been “babied” with lots of low speed stop-and-go driving?
Look in the cylinders with a borescope to check for carbon deposits.

The pinging might be caused from excessive carbon build-up on the pistons which raises the compression ratio of the engine. You might try performing a decorbonization of the pistons.

To do this, purchase a can of Seafoam engine treatment. With the engine hot, remove the brake booster vacuum hose from the brake booster. Adapt hose that will connect to the brake booster hose and will fit inside the can of Seafoam. Take a pair of pliers and pinch off the hose.

Have someone start the engine and bring idle speed to 2,000 RPM’s. Slowly open the pliers so the Seafoam begins to be drawn into the engine. You want to keep the RPM’s at 2,000 while at the same time pinching off and opening the hose to prevent the engine from stalling. Once all the Seafoam has been drawn into the engine shut the engine off. Reinstall the brake booster vacuum hose. Once the engine has sat for a half hour, restart the engine and bring the RPM’s back up to 2,000. Keep the RPM’s at this level until the clouds of smoke that comes out of the exhaust clears.


Does your Mustang have a knock sensor? When they malfunction…one of the symptoms can be engine knock or “pinging.” You might want to look into that. I found one at Autozone for your year Mustang GT.