I recently installed a Dynomax cat back after driving around with a loud rusty muffler for over a year. I hear pinging now (even at light throttle) but I don't know if it started pinging before installing the cat back or after. It has 109K on it and it otherwise runs well. The spark plugs and Taylor spiral core ignition wires are about 5 years old and about 24K on them. Distributor cap and rotor are a few months old. Any ideas why it's pinging? I don't believe it's a bad batch of gas because it's pinging 3 full tanks later. Could the ignition wires outer layer be breaking down? O2 sensor?

I take it is a 5.2 or 5.9 eng ? First if it did not do it before the exh change then you need to make sure the exh did not change the exh back pressure to much. Most of the ECR valves on that year have a solenoid the PCM works but they also need so much exh back pressure to close a valve inside the EGR so it will work and open when it should. EGR is like a poor mans octane booster as it lowers combustion chamber temps. Many cars and trucks as soon as the EGR is unhooked they start pinging from to high combustion chamber temps. When it puts the burnt exh gasses back into the cylinders it wont burn since it is already burnt gasses and it keeps the cylinder from starting more then one flame front and keeps the cyl temps lower.

That said they also have a problem with the gasket on the bottom of the intake leaking and sucking oil into the cylinders and building up carbon hot spots in the cylinder chambers. Sometimes you can tell but looking down in the intake to see if it has a bit of oil laying in it. Just open the throttle body all the way or pull the throttle body off to get a good look. If it is leaking you have to pull the intake and replace the gasket on the bottom of the plenum. Then sometimes you can run combustion chamber cleaner through the eng to try and break up the carbon. If its real bad you may have to pull the heads and clean the carbon.

But I would make sure your EGR valve is working first. The PCM can set a code as it will test the EGR under certain driving conditions as when it opens the EGR valve the 02 sensor will show leaner and the PCM will look for a change in the short term memory right away. But sometimes it takes alot of driving to meet the right terms for the PCM to run the test. If you know anyone at a Mopar dealer they can check it real easy with the scanner. Ron

Thank you for your response. It has the high output 5.9. Original muffler had a hole of a baseball in it so there is probably more back pressure now with the new cat back. Both the EGR and intake gasket are both good points. I do have a good scanner so I'll look for codes. I'll also check the EGR with a vacuum pump to make sure it's not sticking. There is no oil consumption but I'll check inside the throttle body. All good ideas. Thank you.

Just remember if you check the EGR with a vacum pump it has to have exh pressure to it to work. Usually the exh pressure would come up the tube that pulls the valve open and close the exh pressure valve up in the EGR valve so the vacum wont bleed off but will pull the valve open. It also has the EGR solenoid that only lets it get vacum when the PCM works the EGR solenoid. Good luck , Ron