Hi, I have a 1998 Ford F-150 4x4 4.6 142000 miles. It has started missing and running bad part of the time and running fine at times. It runs bad mostly when you first crank it and while the engine is warming up. Sometimes after the temp gets up it clears up but not always. I got these three codes: PO 401, PO 174, PO 308. I changed the spark plugs and fuel filter today. That didnt help. Any ideas?

Joe

 

Hello

P401

Possible causes:

Fault in vacuum supply to EGR vacuum regulator solenoid.
EGR valve stuck closed or iced.
EGR valve diaphragm leaks.
EGR valve or flow path restricted.
EGR vacuum hose off, plugged or leaks.
VPWR circuit open to EGR vacuum regulator solenoid.
EGRVR circuit to PCM open.
EGRVR circuit to PCM shorted to PWR.
Differential pressure feedback EGR (D.P.F. EGR) sensor pressure hoses both connected improperly.
D.P.F. EGR sensor pressure hoses reversed.
D.P.F. EGR sensor VREF circuit open.
Downstream pressure hose off.
Downstream pressure hose plugged.
Damaged orifice tube assembly.
Damaged EGR vacuum regulator solenoid.
Damaged D.P.F. EGR sensor.
Damaged PCM.

P 174

DTC P0174 bank 2 indicate the fuel/air ratio is too lean. The fuel trim system is at the rich correction limit.

Fuel system

Excessive fuel pressure.
Leaking fuel injector(s).
Leaking fuel pressure regulator.
Low fuel pressure or running out of fuel.
Contaminated fuel injector(s).
Vapor management valve (VMV) leaking.
Induction system

Air leaks after the MAF.
Vacuum leaks (vacuum lines and gaskets).
Restricted air inlet.
PCV system.
Fuel purge system.
Improperly seated engine oil dipstick.
EGR System

leaking gasket.
Stuck open EGR valve.
Leaking diaphragm.
Base engine

Oil overfill.
Cam timing.
Cylinder compression.
Exhaust leaks before or near the HO2S(s).
Check intake air system for leaks, obstructions and damage.
Check air cleaner element, air cleaner housing for blockage.
Verify integrity of the PCV system.
Check for vacuum leaks.

 

P0308 - Cyl No.8, Fuel Inj. Test Pin 98

HD1 CHECK POSSIBLE CAUSES OF MISFIRE
Note: Running out of fuel can turn on the MIL and possibly store a Continuous Misfire DTC.

Misfire Continuous Memory Diagnostic Trouble Codes (DTCs):

Possible causes:

Ignition system.
Fuel injectors.
Fuel pressure.
Evaporative Emission System.
EVAP canister purge valve.
Base engine.
Running out of fuel


There U go !

Look at all these areas and U should find the problem.

 

I would start with fixing the P0308 first as it can cause the P0174.
Get rid of the miss before you worry about anything else.
If the plug didnt fix it I would try a new plug wire.
The P0401 is probably caused by a bad DPFE sensor but could also be a bad EGR valve or plugged EGR ports in the intake.
If you do a search here you'll find lots of info on the P0401 and what others have done to cure it.