This is my first Ford. A 98 f150 v6 4.2L.

The other day I stopped to get some gas, and drove on home and all was well. This was Saturday evening. The truck sat overnight. I went and started it up to go to work Sunday and there was a knock in the engine. I couldn't really tell where it was coming from but it was reasonably loud. I killed the engine and started it back a few minutes later and the knock was a little quieter...I chanced it and went on...after less than a 1/4 mile the knock was gone completely. I spent about 6 hours working and the knock was barely audible when I started up. This morning it did the same thing...and quit after about the same driving distance...

I've had a knocking engine before but it was consistent. What could be causing this to go away like that? It's got me hoping that its not any sort of major damage, or something that can be corrected easily.

I will admit I got some cheap gas from a certain "world's largest retailer" gas station....could that be the cause of engine knock? And will it be alright once I run this tank out and get some good juice to my motor?

 

I am having similar problems with my 2000. The knock happens under load at low RPM while in gear. I admit it's scary hearing the knock. I am trying to narrow it down, but it sounds like a weak lifter, or possibly the timing gear tensioner is not applying enought pressure on startup. If I let the engine warm up for 3 to 4 minutes at idle, it never knocks! I am going to drive it until the weather warms up a little more, that is if it last that long!

 

Do the routine, check all fluids, remove the plugs, looking for deposits that might also be on the top of the pistons. If heavy deposits are found, consider one of the upper cylinder cleaners on the market.

 

Any engine noise can be unnerving. The noise you are hearing would appear to be a piston that has gone undersize from a cracked skirt. The piston would slap quite a bit when cold, then heat up, expand, reduce the clearance and quiet down. The slap would become louder with applied load. A loose piston usually sounds like rapping a muffled bell with a small hammer and the noise occurs on the power stroke.

I suggest you take the truck to a specialist who has the experience to diagnose the noise....no sense in running the engine until the piston breaks.

 

Well, I ran my truck down to a quarter tank, and ran some good quality gas in it along with an injector cleaner. Seems that the knock is long gone, and its not shuddering as bad at idle....

I'm hoping thats the last I hear of that noise...made me get all nauseate...

Thank yall for the responses! I was all geared up for people sayin I was an idiot, as has been an experience at other forums....lol.