My neighbor dropped off his 2005 F-150 5.4L 3V complaining of a shudder in Overdrive and was convinced it was a transmission problem, Since no check engine light had been set for a cylinder mis-fire. The battery had been replaced on this truck so all information in the engine computer had been erased, including the stored trouble codes and engine computer had not had time to perform all its emissions system checks yet.

This truck sat the local Ford dealership for a week and they could not find anything wrong because no check engine light was displayed and no trouble codes were set/stored.

Installed my scan tool and went for a 5 minute test drive. It was confirmed all the emissions monitors had not been completed yet, thus no trouble codes would set. However, #5 cylinder mis-fired 254 times. I ran some Seafoam through the engine and the old plug zipped right out with my cordless impact. I installed a new Motorcraft spark plug and installed a coil on plug boot kit. Truck runs smoothly now.

Moral of the story, just because there is no check engine light on, doesn't mean there isn't a problem.

 

Good info. I'm kind of surprised the dealer did not find the bad plug, must have been a lazy tech. They can also get carbon tracking on the outside of the plug and that requires boot replacement. The carbon tracks in the boot will cause a new plug to misfire. I see you rebuild automatics, have you ever installed a 4r70w gear train into an AOD and if so what modifications are needed to the governor and valvebody? I built one for my 66 Mustang and have yet to run it.

 

Yeah, the entire service department at this dealership is lazy and un-trained. I doubt they even hooked up a scan tool or drove the truck any distance.

I replaced the plug boot because the rubber was was getting brittle and the metal spring that connects the coil to the plug was mildly corroded.

I sent you a PM about the AOD upgrades.