Chevrolet Repair: pinging noise, lucas oil additives, air fuel mixture

Question
i have a 1999 new body syle chevy with a 5.3 liter motor.  its 4wd. when its cold out side and the trucks been sitting for a long time it starts up and then it will quite. when i take off it starts up again and dont stop until i reach high speeds. when going i reverse it doesnt have the noise, but if you hit the brake in reverse stopping on flat ground or going down a hill. it started about a week after i changed the oil. I then changed it again, flushed the motor anded some lucas oil additives and castrol synthetic. changed the belts and also plug and wires.

Answer
Hey Lucas,

 Are you sure it is a mechanical sound and not a combustion or timing sound? Maybe have a technical check the knock sensor and fuel trim.  If the knock sensor is not retarding the ignition timing with the computer that could cause a pinging noise.  A lean air fuel mixture could also do this.


Wayne