I had a 5.3 crate motor in my 01 sub installed last year. When it is hot outside and the engine is hot it knocks (pre iginition) under light throttle but not at WOT. I have had the Tech2 update done which helped but the mechanic says nothing wrong with motor.


Any ideas?

 

Its a shot in the dark but have you tried using a higher octane fuel to see if that does anything... there is probably more going on but its an easy enough thing to try to see if it changes..