2010 F150 5.4 3V Triton engine Misfires when Cold

Asked by GuruW6FF8 May 25, 2018 at 03:22 PM about the 2010 Ford F-150 XLT 4WD

Question type: Maintenance & Repair

Starts fine and regular idle for 20 seconds, then hard misfire on cylinder 4
and 8 until engine warms up, then runs like a champ.

Local Ford Dealer said Piston Rings, I don't buy it. Replaced plugs and coil
packs, injectors and sprayed Carb Cleaner around intake manifold to check
for leaks, no change. My Mechanic said Fuel Pressure was in the 40's range
at startup.
Haven't checked compression on suspect cylinders yet. Is there a sensor
that would change fuel intake from startup to running conditions. It idles very
rough for 9 minutes when it's warm out, about 11 minutes when cold. Once
it's warmed up it runs perfect, no hesitation, no burps or anything. Will
continue to run fine between startups as long as it doesn't cool off to much.

4 Answers

74,180

If it only happens on first start up of the day, when engine is cold, it is going to be difficult to diagnosis. Suggest you park the vehicle at a repair shop overnight and allow the mechanic to hook up the live data recorder in the morning. If it is electronic the recorder will immediately point to the problem. Even a mechanical problem will point to a suspect part because out of range readings will be present. You've probably already spent more than the analysis would cost by replacing unnecessary parts.

Do a leak down test for the best evaluation of the suspect cylinders.

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