Hey, just joined here because all my 5.4 searching leads here, my truck in a 2005 F250, but my understanding is the the 5.4 in it is the same as the F150 or same vintage.

Back story on the truck is at 100k miles, 2013, I had a bad misfire after having the plugs done at the dealership. Coil pack here and there didn't solve it, wound up melting a piston and taking the head with it. So at 100k it got a Ford long block, I believe reman unfortunately.

Truck now has 165k on it, so motor has 65k, I believe I've been feeling a loss of power, but more importantly is the random misfiring.

Truck sat for a couple months, started driving it again and got a bad misfire on the highway, with the flashing CEL and all. Got off the highway and topped the tank off with fresh gas, 93 just because. Got home that night and couldn't pull a code with my SCT x4 (truck is not tuned, SCT is locked to the old motor) so I've left it in the truck. Got it to misfire again the next day, and got a Cyl 8 misfire code. In the last week of occasional driving I randomly get a misfire that doesn't last, usually on acceleration.

I have a couple extra Motorcraft coil packs, I've been thinking I should try replacing the #8 with one. I believe they were they brand new ones off the old motor, the new motor came with coil packs IIRC. Is there a way to test the coil packs?

Also, I've heard of Forscan, but I havent dove down the rabbit hole on it and its capablities. Is there a diagnostic function that would be relevant to the problems I'm having?

Thanks

 

Do the poor man misfire diagnosis. Pull the #8 coil and check for spark tracks or bad spots. If good, swap the coil with any other working cylinder. Start engine checking to see if the misfire moved. If not, pull the #8 plug and review it for needing replacement and also oil covered/rich/lean. If it looks okay then swap with working cylinder and restart engine. If misfire is still on #8, swap fuel injectors with working cylinder.

That's where I would start before going all parts canon on the engine. Also, at 65,000 miles, you are close to the 70,000 mile spark plug change requirement. Also due for boot and spring change on all the coils.

In my opinion, I don't know if Forscan would tell you much more than verify the #8 misfire. With OBDII mode 6, you will see the other cylinders and if they are misfiring.

 

If you had a flashing CEL, you should have had a stored code. But assuming you’ve only had a misfire on cyl 8, id follow advice given in post 2.

and fwiw, I would also cure your misfire before introducing new parts. But once cured, plugs and boots/springs.