I'm looking at buying a '97 F-150 4x4, 4.6L, AOD w/ 165K miles on it. It seems to run and drive fine but it has the dreaded spark knock. I'm a little bit familiar with this because my dad-in-law has a '98 that just started doing it. I've read alot of posts and TSB's and evrything says MAF, injectors, carbon, bad gas. All of these sound likely but I was wondering if the cam chains could stretch enough over time causing the timing to be off enough to promote prdetonation. I am not real familiar with the chain setup on the 4.6 so forgive me if this is a dumb thought. Sorry this is so long. Thanks.

 

Hi jimbo8 and welcome to FTE

I really dont think that cam chain stretch would cause pinging. The ignition timing is all computer controlled based on readings from numerous sensors on the engine.
Retarding cam timing like a stretched chain would do usually decreases cylinder pressure at lower rpm where most pinging occurs.
With 165k on it I wonder how much carbon is in the engine? Has he cleaned the MAF? Has he tried different gas?