Pinging while coasting is not combustion related. You have mechanical metallic thingys touching each other. I knew a guy once that thought he had "pinging" while decelerating which is IMPOSSIBLE BTW.....Turned out to be the flex fan just nicking the fan shroud.
As mentioned--cranking compression would tell me all I need to know. I hate threads like this that suck me in and leave me hanging. Lol. J.Rob
