l would like to know if anyone know were the location of the Schrader fuel valve on 08 F150 4.2. I have been looking very had for it. I'm trying to install a aftermarket fuel gauge to it. Anybody that knows please!!

 

It doesn't have one. Why would you be installing a fuel pressure gauge?

 

In 2008 there is a fuel pressure sensor installed. You can read it through the OBD-II system.

 

Ford deleted valve a long time ago .Many people could have used this valve to diagnose bad fpdm on rear axle .It is a high failure item due to salt/water and dissimilar metals ,see sticky for details . It is another case of accountants running the company . Too many plastic parts and overruling good engineering practices . Their mantra is sell the most not make the best .
If you don't know the fpdm receives a signal from pcm that monitors fuel rail pressure on demand with the help of the fuel rail pressure sensor . Many inputs come to fpdm to control fuel pump . There is no more return line to fuel tank it is an on demand system .
Inspect your fpdm it will fail sooner or later ,new ones have plastic standoffs to keep alum off steel .

 

Just to keep track of my fuel pressure and when ever my fuel pump is trying to playing out. By the way, what location do you think I can install my fuel pressure gauge at.

 

Just get an OBD2 reader off ofnAmazoo and an app, like "Torque". $25 for the reader, $5 for the app and you can read all the fuel pressure info you can think of!

 

Its true torque pro will read what pressure it thinks it has on rail . Good for some testing but not if fuel rail pressure sensor bad . I don't think fuel rail pressure sensor failure is common . The old shrader valve did require a special gauge and was messy . Not convenient to carry around with messy fuel in line and fumes . The pump /wiring and no 1 the fpdm module high failure rate . Low fuel stresses fuel pump, it cools it when there is plenty of fuel . There is a vacuum line on fuel sensor to adjust for acceleration .
The torque pro $5 app/android phone /and cheap bluetooth reader will give you tons of info to work on this truck and other vehicles also . The android phone does not need to be active an old cheap one will do .
And we have a very good torque pro teacher on here ..

 

Keeping track of fuel pressure ... In the 'Fuel Rail'? - relative to what?.

Your reading would be _all over the place_ if your gauge reading is relative to atmospheric pressure. ( This is probably the reason the Schrader fuel valve was eliminated.) It would not tell you much about the fuel pump. Except that it responds to the driver module duty cycle control signal.

Like others have suggested - getting the reading from OBDII is far best. The FRP sensor output is 'relative to intake vacuum' so from OBDII you know exactly what pressure differential your injectors are working under. AND the 'duty cycle' commanding the fuel pump driver modules is at any given moment.