This one has me stumped; I have a 2001 F150 with a 4.2 V6 that ran great one day but when I hit the key the next day the engine exploded!!! I don't mean just a backfire, it literally blew the valve covers apart!!! The only thing I could think of was that maybe it jumped time, but when I tore it down to the timing chain it's still in time but motor is locked up. I even put a 6 foot pipe on a pipe wrench & cannot budge it... Anyone have any ideas as to what happened?

 

That's a new one! Possible leaky injectors?

 

leaky injectors or leaking coolant???

 

That's the only thing I could think of too, leaky injectors.

 

Seen it many times. You either have leaking injectors or have one that finally shoved enough gas in the oil to be dangerous. The engine will obviously need replacing now as seals are now crammed into the crank which is why you can't turn the engine....most likely. Normally that's the issue with the engine being locked up but on rare occasions it can turn a piston sideways in the hole. All things considered, if you intend to keep the rig I'd be looking for a complete replacement as the top end accessories are now toast too.