Ford F-150 Lariat, P0300, P0304, P0305, P0308

Basic diagnostic procedured for Trouble code P0300, P0304, P0305, P0308

VEHICLE: 2005 Ford F-150 Lariat 5.4L, V8, MFI, SOHC, VIN 5, Eng Desg -, Eng Version Triton
MILEAGE: 101000

Concern: After the engine reaches operating temperature it loses power and misfires and backfires through the intake on hard acceleration.
The Powertrain Control Module (PCM) set Keep Alive Memory (KAM) codes P0300, P0304, P0305, P0308, and P0420.
Fuel pressure is staying between 35-55 psi all the time.

Tests:
1. Remove and inspect the condition of several spark plugs. If the spark plugs are worn from excessive usage, replace the entire set of spark plugs and plug boots. Use the guidance of TSB 08-07-06 to remove the spark plugs with the greatest success of plug removal without breakage.
2. Check the output of the Coil-On-Plug (COP) units on the cylinders denoted by misfire codes by installing a spark tester between the COP unit and ground with a 3/4-1" air gap to verify that the COPs will produce a strong and consistent spark with a bright bluish color. Replace any suspect COP unit.
3. If replacement of the spark plugs and any suspect COP unit results in the continued recurrence of engine misfire and backfire, check the exhaust backpressure for an indication of a restricted catalytic converter. Replace the converter(s) as needed.

Potential Causes:
Worn Spark Plug(s)
Spark Plug Boot(s)
Defective Coil On Plug(s) (COP)
Restricted Catalytic Converter

Confirmed Fix:
Replaced Spark Plug(s)
Replaced Coil On Plug(s) (COP): A couple of COP units were failing.
Replaced Catalytic Converter(s): The driver's side converter was restricting flow.

Ford F-150 Lariat, P0300, P0304, P0305, P0308