I have a 98 expedition with the 5.4 v8. It blew a spark plug out and i had it at a friends shop being repaired. he left town and the vehicle sat with the intake manifold off for over a year. I recentl retrieved the vehicle and put the parts back on. when we cranked it it ran fine the first time. second time we cranked it, (2 days later) it had a bad miss. carried it to shop and mech said low compression in one cylinder. there is no blow by and no noise from throttle body, so I think a exhaust valve is stuck open. should I try some kind of kleaner through throttle body first or do you think it could be a rocker arm slid off or something like that. Haven't removed valve cover yet. I was told by a tech at a machine shop that 5.4's were bad about doing that after sitting for a long time. anyone had that experience? an advise would be appreciated. I'm a amateur here. thanks

 

What did the shop do to repair the blown out plug? Have a leak down test done on that cylinder. Didn't happen to be the same cylinder the plug blew out?

 

Edit: Okay, never mind then lol.

 

Yes, same cylinder. He fixed the plug with a kit if some kind