I have a 2005 f150 5.4l 4x4 168,000m

it throws a p301 code and runs really rough between 50-65 mph...check engine light flashes...i just changed the number 1 spark plug and coil pack...now it throws 301,303, 171 codes..

advice?

 

301 and 303 are cylinders 1 and 3 misfiring. That is why check engine light flashes. A code P0171 may mean that one or more of the following has happened: The MAF (Mass Air Flow) Sensor is dirty or faulty Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry. There could be a vacuum leak downstream of the MAF sensor Possible cracked vacuum or PCV line/connection Faulty or stuck open PCV valve Failed or faulty oxygen sensor (bank 1, sensor 1) Sticking/plugged or failed fuel injector Low fuel pressure (possible plugged/dirty fuel filter!) Exhaust leak between engine and first oxygen sensor
Read more at: http://www.obd-codes.com/p0171

 

How many miles on the engine and when was the last tune-up ??

 

i changed the coil packs...problem solved.

 

Glad you got it fixed!