Hello All! I have a 1990 F-150 4x4 with a 5.0/automatic. I am getting a misfire under load at slower speeds. According to a mechanic, it's a burnt exhaust valve in # 8. Could this be coil related??? What is the test for a burnt exhaust valve? Any guidance greatly appreciated!

 

go out to your truck tonite in the dark and see if your not sparking from wire to wire or something like that. Compresion test should tell you if you have a burnt valve. Could be a coil pack, switch the wire and see if it still does it.

 

Thanks! I'll give it a try this weekend and let you know how I make out.

 

No arcing.....

Compression tested confirmsa bad # 8 valve.

I'm thinking used heads so as not to put a strain on the lower end. Bad idea or good?

 

I don't think using a used head will prevent extra strain on the bottom end. How about just machining the one valve seat and replacing the bad valve. If it ran pretty well before then you should be O.K. Otherwise I would go for a complete long block and have a good reliable motor for a while