getting ready to diagnose fuel delivery, starting with changing fuel filter as I don't know when it was last changed,
what I know from scan tool is 32 to 46psi at fuel rail, spec is from 40 to 70psi, fuel pump control module is receiving 12v.
I changed air filter and thermostat both made a difference, and new fuel pump control module, which made a difference.
after I change fuel filter, the next step is to check vacuum at fuel pressure regulator, which should be same as manifold, not sure how
to go about this. and wonder if manifold vacuum number would be available threw scan tool. guess i need a vacuum gauge to check both numbers. there is a vacuum line plugged off near passenger side throttle body, not sure where/why its like that or where it goes to or from

any thought would be appreciated, thanks

 

- ID your truck details
- ID the problem/condition you’re trying to address
- ID what psi is at KO/prime before starting (s/b ~60-70, and ~ 38-40 while running.


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I'll play devil's advocate here and say I don't recall anyone ever reporting that they solved a problem by replacing their fuel filter, but I have seen a handful of folks that created a problem by breaking off the fuel line or the connector at the filter.
So, while it's not a bad idea, it might not do you any good.
40 psi at idle is plenty. The only time it goes up to 70 psi is when it first primes before starting from my observation.

What is the concern that is driving testing the fuel delivery?

 

04 f150 4.6 STX harder to start after warmed up but always starts first crank. fuel pressure at idle 32 to 46psi back and forth the below 40 number at idle and slower start alarmed me. Is that just the way these trucks are?
how do I get the prime psi data?
the book said make sure the fuel filter doesn't have more than 30000 miles on it before doing any tests.
thanks

 

your fuel pressure appears to be fine.

prime psi would be upon on, prior to starting.

don’t know anything about mileage or maint history, so it’ll be another 20 questions without more info.

 

Without a full description of your vehicle (Is it 4 x 4?) this is a guess about the plugged vacuum line you mentioned, I will assume it is a 2wd. That plugged vacuum line is not used on 2wd vehicles, on 4x4 it is used to operate the Independent Wheel Ends (IWE) that operate the 4x4 (engage/disengage) from the switch on the dash. I am pretty sure most auto parts store rent vacuum gauges as loaner tools.

 

thanks,

 

thanks, fuel pressure improved after replacing fuel filter, between 38 and 44 psi, I think the fuel pressure regulator in pump isn't holding the pressure in rail for quick start. (possibly pump can't reach quick start psi levels)
not sure how to test regulator since it is in tank on pump, and there's no Shrader valve on rail.
thanks, that plugged vacuum hose must be for 4*4, I would never have figured that out
I don't know the maintenance history of truck the previous owner of 5 yrs (82) pasted away loading truck with some firewood. I bought truck from his wife
No real rust 85000 miles new tires, 4500$, it needed serpentine belt, thermostat, air filter, fuel filter, i changed plugs, changed oil, then
joined the F150 forum, since a international forum helped me with my vintage motorcycle.etc.....

 

Fuel pressure of approximately 40 psi is good (38 to 44 OK). Fuel filters do not usually make much of a pressure difference unless it was full of debris which yours apparently it was. On this vintage (2004 thru 2008) the fuel pressure sensor regulator is on the passenger side fuel rail (at least it is on the 4.6 engine). The common failure item when it comes to the fuel system is the Fuel Pump Driver Module (FPDM) which is located on the frame crossmember above the spare tire. You are good for now but at some time in the future it would be a good idea to take a look at the FPDM as they fail due to corrosion between the back side aluminum cover and the frame rail and cause all sorts of starting and running issues without throwing a Diagnostic Trouble Code (DTC). The aluminum cover cracks and exposes the circuitry to the elements. There are thousands of post concerning failed FPDMs. I carry a spare in my glove box.

 

thanks, i installed a new FPDM it seemed to help, i put it on before getting a spare rim and tire I found new psi numbers from book, stating 28 to 55 psi running is spec. 45 to 55psi at start up
I just took another look for my fuel pressure regulator none to be found, there is a fuel pressure sensor attached to driver side fuel rail.
i think my fuel pressure regulator is attached to the fuel pump, if someone put wrong pump in there, that would explain my no quick start.
maybe someone has swapped fuel rail with no fuel pressure regulator mount, that would explain the plugged vacuum line on passenger side near throttle body, does yours have the fuel pressure sensor on driver's side fuel rail like mine. ?