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SuperBob, Ford Senior Master, Mazda Senior
Category: Ford
Satisfied Customers: 2609
Experience:  18 years Ford, Lincoln, Mercury, Mazda Dealer ASE master, diesel certified. Specialize electrical
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2005 f250: 5.4l..p0171 and p0174 codes, it..vacuum leak..fuel filter

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I have a 2005 f250 5.4l and it has p0171 and p0174 codes, it has the upgraded vacuum tubes on it already. One tech said it was a vacuum leak under the plastic air intake?
The truck runs fine, with a slight sluggishness on take off. Could it be a fuel filter?
HelloCustomer yes it could be a dirty restricted fuel filter, or even a weak fuel pump, a dirty mass air flow sensor could also be suspect, un-measured air entering the engine in any way, or low fuel pressure can cause these lean codes. I would start with the fuel filter, clear the codes and drive it to see if they return, if so we will need to get a fuel pressure test done to see what the fuel pump is doing.
Customer: replied 7 years ago.
How do you check fuel pressure?

This model truck will require a special tool to install in line at the quick connect fitting on the back drivers side of the top of the engine and then a fuel pressure gauge would be installed to this T fitting tool.

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