I have a real problem with gas ping on my 2001 Edge. It has the 4.0 ltr engine, automatic, air,4x4,ported injection. I have tried everything to get it to stop. Prem. gas, octane booster, Prem gas and octane booster combined and still get the ping. No check engine light, so the local dealer says the sensor "should" be ok. Any suggestions ??....................Really frustrated about it.