You actually mixed two terms:
Preignition- Ignition of the mixture due to glowing carbon deposits in the chamber. This occurs independently of the spark, usually prior to the plug firing, as the piston is nearing top dead center. Often accompanied by dieseling (engine continues to run after turning the ignition off)
Detonation- occurs due to fuel with an octane rating too low for the demands of the engine. Occurs after the spark plug fires, but an area ahead of the advancing flame front ignites and the two flame fronts collide.
Both conditions produce a ping, a sound like bb's dropping on sheet metal. The full sound of the explosion is muffled by the surrounding engine parts (Out in the open it sounds like an M80 going off, as was demonstrated to me back in automotive school many years ago.), but either condition is very hazardous to your engine. It can knock a hole right through a piston, I've personally had it happen.
Yours appears to be detonation. It can be due to excessive carbon in the chamber raising the compression beyond what regular fuel can deal with, or a mixture that's too lean. Check thoroughly for vacuum leaks. Timing and fuel air mixture are a bit more complicated to alter on these new vehicles.
Regarding the tranny, a fluid change would be cheap insurance against unnecessary wear. I wouldn't have it flushed, just a fluid and filter change.
1999 Ranger Extended Cab, 4x4, 4.0, automatic.
Last edited by shovelmike; 12-05-2011 at 07:03 PM.