Ok so I have a 1989 F250 4x4 with a 351W and 24,xxx miles. When I first got the truck I had a knocking issue but I retarded the timing and it disappeared. Now I just replaced the manifolds, valve cover gaskets, and hooked up a catalytic convertor and muffler which it didn't have before. Now we'll the knock has once again come back. If I retard the timing down real low the knock goes away but the engine had absolutely no power. If I move the timing back to where it should be the knock comes back. The knock doesn't sound like it's coming from down low in the engine. Depending on where I set the timing the knock becomes louder or much quieter. So not really sure if the engine is down for the count or is this simply an ignition issue due to bad fuel filter, vacuum leak, or some other cause. Any help is greatly appreciated!

 

My truck was knocking and after all the headache I finally found out a spark plug was loose.

 

Just replaced all of those so not that unfortunately

 

Dang.. Another thing could it be an exhaust leak? Coming from the manifold.

 

Just replaced the manifolds to haha no leaks from there

 

Lol ok. Oil been changed recently and how thick of an oil are you using?

 

Yes changed the oil about two weeks ago and I forget what thickness but it's the recommended thickness from Ford for that truck.

 

Pretty sure it was 5w-30

 

Check for codes. Also, inspect the EGR setup. Could be a stuck or bad lifter as well. However, check for codes first and proceed from there.

 

Is this the oil that has been used in the truck? The reason I say that is because I used valvoline in my truck one time (I usually use havoline) and the truck knocked and acted like it had no oil pressure. Changed the oil back to havoline and it quit.