P0306 (ok #6 missfire) with P0171 & P0174 --- Do I chase electrical or fuel or both. Affraid to assume anything but probably would normally address the missfire electrical first....Don't want to go down that 'primrose path' if others have been there first!

 

306 is a hard/firm missfire fault because it's passing raw gas through the cats.
Do that one first.
The others are usually indicating an air leak in the intake at some point.
Often roted/split hoses etc.
Good luck.

 

Thank you Bluegrass!! New Platinum Motorcraft plug and new Belden plug wire...No more miss on 2 approx. 10 mile trips. On second trip 'jumped on it' on a gravel road and got a cel with the P0171 & P0174 System lean bank 1 and bank 2. Inspected all hoses/lines (that I could find) with no sign of deterioration/cracking/leaks. Freeze frame for P0171: fuel supply 1= CL/fuel supply 2=CL-Fault/calc load%=78.02/ECT(F) =188/STFTB1%=-(minus)14.06/LTFTB1%==25.00/STFTB2%= -(minus)12.50/LTFTB2%=25.00/engine RPM=2153/speed MPH =31. Next plan is to change the fuel filter[been quite awhile] and see what normal driving will do. Any further suggestions would be welcome for consideration(and your explanations are great!)

 

Check the vac at hot idle. A lower than normal reading, but fairly steady would indicate a leak in a line usually. Follow the hard plastic lines everywhere, especially on the passenger side, around the firewall/battery.

Nothing cracked there, remove the PCV line from the valve cover and the rear of the intake. The actual line is semi rigid plastic, with a foam insulation jacket. If the fitting at the back end isn't leaking, try flexing the line itself. Pretty common for a split or break inside the insulation. Often, it's just the rubber hose connector from the plastic line to the intake.

If the vac checks OK, then the problem is between the throttle body and the air filter. Either a leak in the ducting, or a dirty/faulty MAF sensor.

I did repair one truck that had a fried rubber vac line from the intake to the brake booster. If that was your problem though, you would feel that in the braking.

Dave

 

New fuel filter installed. 2 short trips approx. 18 miles total and normal for now. MAF/TPS/IAT/air filter new recent for different problem(fixed). Now for normal use and see if all is well. Thanks for the tips!