I recently replaced the spark plugs in m 2005 F-.

ANONYMOUS

MEMBER
2005 FORD F-150
107,000 MILES

I recently replaced the spark plugs in m 2005 F-150 5.4 3v due to a sputtering problem on acceleration. The truck was running fine after that. I now have a misfire that came on all of a sudden. I stopped at a ford dealer that I was close to when it started and they diagnosed it as cyl 8 misfire. I replaced the coil pack and the fuel injector on that cyl and the prolem still exists. What else should I check?

1 Reply

CARADIODOC

MECHANIC
33,742 POSTS

Check the compression. Swap the spark plug with one from a different cylinder to see if the misfire moves to that cylinder. Don't replace one injector. They don't fail that often but the screen can become plugged or varnish buildup can affect its flow rate. Now you have one injector flowing a lot more fuel than all the rest. Instead, swap the injector from the misfiring cylinder with one of the other cylinders, but not the same one you moved the spark plug to. If the misfire moves to a different cylinder, you'll know the cause by what you moved to that cylinder, spark plug, injector, or coil if you have coil-on-plug.

Check the EGR system for passages blocked with carbon. As the individual tubes become blocked, those cylinder run fine. The full exhaust gas flow goes to the one last cylinder that is not blocked, so that one misfires from not enough fuel and air.