Got question for the mechanics out there. Got a 99 ford expedition 4x4 5.4 liter.
vehicle was running bad so we replaced some vacuum lines, pcv valve and change plugs. first after replacing vacuum lines it ran great for 2 weeks then started running rough again. We change the other items I mentioned it still is running bad. a mechanic I know troubleshooted it down to the pcm. when I change the pcm(after matching XL1F-12A650-FE number up) it won't start. Disconnected battery for 10 mins then tried again still won't start. But it will if the original pcm is in but runs rough. Anyone got any ideas I'm stumped.