Monday, May 14, 2012

2004 Ford F150: Engine Misfire and Lean Code?

Replace Spark plugs and coil but still Engine misfires and OBD code P0171 is coming up.

First check that do you smell Fuel in the cab or any thing like a fuel leak is noticed.
Also the Check engine light will flash.

The check engine light flashing means the PCM (computer) is still seeing a direct engine misfire and if the spark plugs and coils are all new then its possible you still have a problem with one or more. Start troubleshooting by removing all of them and rechecking to be sure none where cracked during install and when reinstalling them be sure to add a small dab of dielectric grease to each boot to assure there is no spark leakage down the side of any of the spark plugs. The lean code P0171 is in most cases set due to a vacuum leak and on  5.4L engine  its usually one of the ports on the rear bottom side of the intake, there is one on each side of the engine, one is for the break booster and on is for the vapor management valve. Have a look at both for signs of rotting out and leaking.

This details will help.

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