Runs lean
Asked by GuruVPP1H Sep 13, 2018 at 03:34 PM about the 2008 Ford Expedition
Question type: Maintenance & Repair
I have a 08 Ford expedition with the 5.4 in it I have
two codes p171 & p174. I've changed the mass
flow sensor , checked fuel pressure witch is 35psi
koer. Is that to low? I've checked my cats and they
are good. I've checked for vacuum leaks , I've had
someone put a scanner on it test drove , everything
is working fine . But the fuel mileage stinks 10.5 in
town and like 12 hwy. It's idles fine . But it starts
jumping and jurking when I give it gas. Dealership
told me that it needs cam phasers.but I hate to do
it and that not fix it. Any ideas?
6 Answers
I would check the fuel pump spec I seem to remember 60 psi but I might be wrong ask dealer for spec.
Possible vacuum leak, bad O2 sensors, exhaust leak, dirty fuel injectors or low fuel pressure. 35 psi is at the low end of acceptable pressure.
If your phasers are bad I would look into a cam phaser elimination kit. Misses can be caused by bad spark plugs or coils.
From what I could find on the web your pressure is OK. It is really hard to find reliable fuel pressure specs on the web. I would confirm this in a repair manual or in a call to your Ford dealer.
But if it was a bad o2 sensor wouldn't it show up on the scann tool?
