ok i have a 1997 f150 4.2l, i posted a few times about the problem that developed right after i changed plugs and wires, it just ran like crap and had no power, well after a while of lookin at what i could do i took it in, now i saw shortly after i changed plugs #5 burnt off part of the plug, and the scanner said 4 and 6 had a miss, plus lean problems, so i took it in mech. figured vacume problems, cleaned inj. and he did some stuff with the egr valves, slapped it all back together to find out now #5 is completely dead no compression!!! so where do i go from here, is it the piston, valves?? any suggestions! it will be spendy i know prolly gonna have to pull the head!

tom

1997 f150
5 spd. manual
flareside

 

Lean combustion frequently results in burnt valves so I suspect you are going to need a valve job. The piston should be fine.

 

Just removed the heads on my 4.2 because of no compression on one cylinder. The exhaust valve had a hole burned in it. You need to replace the head(s), the O2 sensors and the injector on that cylinder.

It's not such a bad thing except for the $$$ because you get new intake gaskets and a more reliable engine afterwards.