hello everyone, im working on my parent's 1999 Expedition, 5.4. Truck currently has 205,000, engine was rebuilt 6 years ago, aprox. 80K ago.

3 months ago, the truck decided to blow out the #6 spark plug. my colleagues and i chased the threads, were able to save the head, we went ahead and replaced all 8 plugs, the coil on that cylinder ( it was damaged in the blowout) and cleared the codes. also had the local repair shop do a fuel injector flush, to keep things tidy.

a month and a half ago, 4000 miles past the first incident, the truck developed a random misfire, and also threw a Cylinder 7 misfire code. the truck would not accelerate over 55 mph. once again, my colleague hooked up his scan tool, and after some testing, decided that the #7 coil was faulty, and a few others were testing weak. replaced the weak coils, truck was driving agin.

150 miles later, the truck was acting up again. i decided to attack it solo, replacing all the non replaced coils, so now all 8 are replaced. still had a random misfire code, and a Cylinder 7 misfire code.

so, now im still stuck with a truck that randomly misfires. it will occasionally work itself out of the misfire, running great for a while, but the misfire returns. the scan tool that has been used is a very nice Snap on unit, it stores all previous codes from the other times this truck was hooked up. today, we were looking through the history, and noticed two codes that we seemed to overlook.

1) EGR codes
2) knock sensor codes

i cannot give you the exact code numbers off the top of my head, and i am by no means a wizard when it comes to engine diagnostics, i am more of a brake and suspension guy myself. one of my friends said that he has seen several times where a dirty and clogged EGR valve has caused a misfire. the other guy said he has heard of a knock sensor causing misfires before.

so, given this information, can anyone point me in the right direction? im just trying to get this truck back on the road, driving safely for my parents, so I can get my old pickup back to drive.

 

Best way to single it out is to unplug the coils one at a time and then back in if it sounds like nothing changed that is the bad one. Also if your not buying ford or something else that builds a reputable COP you can see several of them go out after a short period of time. You also want to use motorcraft only spark plugs the system is very finicky. I have motorcraft with MSD Coils i have not had to replace any of them in the last 3 years knock on wood. I also recommend blowing out the around the coil ensure its dry with no debris. I would install the boots with dielectric grease to ensure you can pull them off with out them ripping. hope that helps.

I was given this advice from a very good ford dealer mechanic and after the truck was having all sorts of issues with it before it helped me iron them all out.

 

i agree with everything you say, the coils are all motorcrafts, ive been through the whole pulling coils, and swapping coils routine. im now trying to figure out if the EGR or knock sensor codes will lead me to a random misfire.