I am stumped here gents and need some help.... I have a 2000 F150 V6 4.2L with 167000+ miles, I have a cold knock my oil pressure is good but when cold it knocks under a load when in park or neutral it doesn't. When truck is warmed up the knock goes away, the truck runs was very good no lose in power or gas mileage just a kicked to my pride with this knock I also noticed a slight knocking (pinging) sound under the engine when a slight acceleration is given if i apply a hard acceleration you will not hear it, I change the fuel grade and did my tune ups and change all filters. PLEASE HELP I'm loosing my mind trying to figure this out.

 

A stab in the dark and its free, if this is an auto trans, remove the cover as if you were going to change the torque converter fluid. Inspect for cracks around the four nuts securing the converter to flywheel. Also try to look more center of these nuts. Cracks also occure at the bolts securing flywheel to crankshaft.

 

Esquibelao, did you ever figure out what was causing the noise? I have the same truck with the same miles and the same symptoms. I haven't looked at the flex plate yet - is that hard to do? I thought that I read that ford redesigned the flex plate in 99 - hmm can't find it now though.

 

Its likely just piston slap. My '97 does the same thing.
The pistons rattle around and make noise when the engine is cold, but once the engine warms up the pistons expand to the point where they no longer rattle enough to make noise.

 

F150chimp, pull off the cover exposing the flex plate and look for cracks around the four nuts securing it to the torque converter. Also need to look at the 6 bolts securing the flex plate to the crankshaft. Have seen both places cracked. Reread the last entry about the piston slap, what was said is true, there can be engine noises due to piston slap. Have a great "drink beer in the garage story", about same subject and a trouble shooting engineer from our beloved FOMOCO. Think I'll forget the story and have another beer.