Hello all,

Truck info: 2009 Ford F150 XLT 2WD 5.4L 75K Miles

I am new to the site and just needing some help if possible. I have been having this issue for the past few days now. When I first start my truck it will idle very rough and will get misfire codes for cylinder 7 and 8 (sometimes 8 not always). I have been researching this issue for the past few days and have come up with nothing. I changed all spark plugs, I swapped the coils to opposite side of engine, swapped the fuel injectors to different cylinders and still see the same issue. the kicker that I am mainly having a problem figuring out is the fact that after the truck warms up for about 10-15 mins the truck will run just fine the rest of the time until you shut the truck off and let the engine cool off. After the engine is cooled off and you start the tuck back up the issue does return once it warms up though it does go away again. after swapping everything around the issue did not move so for the most part I'm pretty sure that everything is still good the only things that i really haven't checked would be an electrical issue but with the issue only happening durring the time that the engine is still pretty cold that leans me away from that. any help would be greatly appreciated.

Thank you.

 

This sounds 100% like an electrical signal issue, either from the ECM or the wiring to those cylinders COP's or injectors. The fact it comes and go somewhat predictably with engine temp is one clue. Another is even when parts are swapped the issue stays with the same cylinders.

I would follow the wiring harness from the COP's/injectors to the single larger plug that connects to the chassis wiring harness that eventually leads back to the ECM. Separate that plug, carefully checking the individual terminals, cleaning as needed.

Check the ECM itself for damaged or corroded terminals, carefully clean those if needed.

BTW I believe its a best practice to disconnect the battery negative terminal first, leaving the vehicle sitting for at least 15 minutes before working on those connectors etc. Others here will correct me if this is wrong.

HTH

 

I have a 2003 4.6L F150. Every time I go to the car wash and water gets on top of my engine it always make the cylinder 3 misfire. Clears up after a few miles. I also had a problem with the PCV tube that made it idle rough. if it's not an electrical problem try running some sea foam or B-12 through it.

 

You may have an intake manifold leak. Especially since it happens cold and after it sits for awhile. What happens is unmetered air enters through the manifold gaskets while the engine is cold causing a vacuum leak around the ports for cylinders 7 or 8. As the engine warms the seal improves. A scan tool with fuel trim data could confirm this.