Im still battling a p0171 code on my 2000 f150 5.4. I checked the fuel pressure at idle it sits at 31. I remove the vacuum line off the regulator it goes to 41. When i give it throttle when in gear it will maintain at 30. And when i shut the vehicle off completely it will maintain 38. Just looking to see if this is correct numbers. I was trying to determine a weak fuel pump.

 

The fuel action is normal and good.
You have an air leak.
Check out all the hoses and fitting that are for vacuum.
The rear of the throttle body riser where they collect many lines.
If your idle is not very rough to use as an indicator for sprays tests, you need to use a Scanner looking at the fuel trims for reaction to spraying something like Brake Clean along the intake each side where bolted to the head ports.
In the center, projecting down into the valley area, is another manifold cover with gaskets. Look between the vertical runners and you can see the area near it's bottom.
Spray at it from between the outer risers on each side for leak tests.
When you hit the leak location area with spray the fuel trim tables will instantly try to recover as well as some RPM change.
If you find a gasket area to be the fault, it means the whole intake has to come off to replace them.
I know it's a pain to find, and the use of a Scanner but it's what has to be done to find it if it's not easily found otherwise.
This why there is Scan tool to use like a doctor needs tools to use..
Good luck.

 

Ive gone through like 2 cans of brake fluid and cant find anything I've sprayed like everything. I also changed to the fuel filter and throttle position sensor. And its running really rough like it shakes at a idle and 0-30 it shakes but 40+ its get pretty bad it shakes and shudders pretty good. Like a month ago i was driving and got gas and as soon as i turned my truck on it has ran bad ever since. Just one day it went from running perfect to running like complete garbage all in one stop.

 

Update: So i just went and scanned the computer again and this time it actually didn't have a P0171 anymore is it possible i got a bad coil on plug without setting off a misfire code?

 

Update: So i just went and scanned the computer again and this time it actually didn't have a P0171 anymore is it possible i got a bad coil on plug without setting off a misfire code?

 

Are you experiencing any misfires symptoms? If not, then you aren't having misfires, go back and look for vacuum leaks.

 

I actually just found the issue i feel pretty silly now the #4 injector wasn't connected and its running great again.

 

You had to have a P0354 code from that plug being off.
How did you miss it and the CEL?
The 171 code will be back if you did not positively find the leak.
Don't use brake fluid for leak testing.
It's to corrosive and to heavy in viscosity and messy for "fast leak test response".
Use a light high volatility spray that will get through the leak area fast..
Good luck.

 

Ya im not sure why it didnt throw a misfire code on cylinder 4 but it was definently the issue. As far as the p0171 code i replaced the 2 dpfe hoses and thats it.

 

Well again, the DPFE hoses have no intake vacuum on them. Can't be the cause of a 171 code.
Look where they go! To the EGR tube between the exhaust manifold and the EGR valve.
Codes involving the EGR system are in the P04XX number range.
When you report things that don't make sense, it's picked up immediately and suggest guessing.
A way to know is look at the code descriptions as an initial guide to the system involved..
If you don't look and think, your chasing your tail.
Good luck.