i rented a fuel pressure testing kit from oreillys and put the connector that fit onto the little valve on the fuel rail that goes to the injectors, and then screwed the gauge onto it, but i can't get it to read anything.. what am i doing wrong? i even tried using the inertia switch to relieve the fuel pressure.

 

Why are you reliving pressure if your trying to read it? Be sure its the right fitting on the fuel rail to test it and the relief button( if that gauge has one) isn't open either. Then turn the key over a few times to prime the system and that should give you your reading.

 

The last guy to rent that guage might have messed up the fitting. It's a "schrader" valve, just like on your tire's valve stem and your air conditioning system. If the center of the valve is not pressed in it will not open. After you put the adapter/connector on put a rag over it to shield your eyes and push the little tit in with your fingernail. There should be pressure/gas coming out. At least a trickle.

 

If your truck isn't running, it might not be getting any pressure to read. Try the gauge on another ford with a schrader valve and see if it works. If it's a new kit, it could have an o ring in the connector that's too big to allow the valve to depress.