recap: 2003 f150 5.4 fx4 around about 102K miles, wouldnt crank the other day thought it was fuel pump/filteer. well the morning after that we tried and it started up and ran perfectly, were thinking stuck relay maybe??
anyways FINALLY talked him into changing the fuel filter. lord it was gross

NOW! truck misses BAD 50-70 mph. he said he took it and got codes read and came up with oxygen sensor codes, i havent hooked my OBD2 up to it yet but i will tomorrow when i get time,

any suggestions and if it is the 02's how would that make it miss, he said the guy that read it said it was lean

 

Major vacuum leak. Check the PCV system, especially the elbow behind the intake manifold, it rots and cracks. The lean codes (I assume P0171 and P0174?) mean the O2's are doing their job and reporting an uncorrectable lean condition.

 

ok so i checked everything out, I couldnt find a leak, is there something you can get to help find a leak, i know i had a exhaust leak on my ranger and couldnt find it so i bought some seafoam (back when it smoked like hell) and found it easy as heck. anything like that?

 

did you ever find out what the codes were?
what all was done to the truck so far?
may have a weak pump if that filter was real bad. check the pressure.

 

no codes actually he said when he gets up to 50-70 (when it starts "missing") it brings up the check engine light, he had plugs changed at about 102k, and fuel filter changed last week and im pretty sure it was horrible, since we drive through the same stuff and i change mine at 10k and he has never changed it before this.

 

i would check the fuel pressure. since the filters never been changed the pump may be weak now.

 

ive heard that, i had to change a fuel pump on a chevrolet tahoe because it went bad after we changed the filter. how do i check the fuel pressure, and what is it suppose to be?

 

there should be a fitting that looks like an air valve on you fuel rail. they make a kit to hook up to that. also pumps generally make lots of noise when they go bad

 

well his pump sounds normal..... ill try that parts store have those?? yea i know the pressure release for the fuel is, so what is the pressure suppose to be around

 

your best bet would be to take it to autozone where they do a diognostic for free. i could find it online but it would take some doing.

 

another idea is to run two bottles of injector cleaner in a tank of gas. you can get a particle breakup when you remove the filter that will clog the injectors.

 

what like seafoam, or techron. which one would be the best

 

BG44K is the best, followed by Techron.

 

alldata shows 28-45 psi running and 35-45psi koeo. when its running pull the vac line off the regulator and make sure the pressure jumps up a little bit-just to make sure its working as it should.

 

ok so i pulled the codes, they are P1151 P0172 P0175 and P0174

all oxygen sensor codes, where do we go now, he wants to replace the oxygen sensors, i told him to hold off until we can figure this out. hes ready to get this fixed so he can sell it and get a new 3/4 ton