2003 ford F-350 with a 5.4L. I changed spark plugs and a couple coils. The misfire we had is gone, but it keeps throwing a P0171 code. I've cleaned the MAP sensor, checked hoses, checked pcv and hoses, I checked the exhaust manifold for leaks or cracks, I checked the intake manifold for leaks, changed the O2 sensor on the passenger side (Bank 1 I hope)..And the fuel filter is only about 6 months old. I'm not sure what else to check. The LT fuel trim is right around 23-24%. Any suggestions please?
Hello and thanks for your question.
Having trims that high there has to be a fairly large vacuum leak. Are you sure you checked the back PCV elbow where it attaches to intake? Did you physically remove it and see if it is collapsed?
Yes, pulled that hose and valve off and checked them, they are ok.
Have you tried monitoring fuel trims live and spraying some carb clean around intake/vacuum lines and see if the trims change? Pretty much every time I see trims that high there is unmetered air entering engine, you could also try smoking the intake.