A fuel pressure gauge measures fuel (gas) or (diesel) or any type of liquid. It does not measure air. The "in line valve" is called a schrader valve. This valve can be used to inject air or liquid -- or (in this case) it can be a devise that allows testing on a pressureized system.I think you are mistaken when you say that air is being measured. If it is then there is fuel leaking somewhere -- you'll be able to smell it.
Anyway -- when you install the pressure gauge and turn the key on, the pressure should come up (we will talk about how much pressure in a moment). When you turn the key off the pressure should remain steady for a few minutes - and then slowly go down. If the pressure is going down quickly and obviously - then the fuel pressure regulator is bad or worse - leaking.
The fuel pressure should be at least 53 PSI up to 65 PSI -- 55 to 63 PSI if perfect. 50 PSI is kind of low. I know that it doesn't seem like much, but these intake systems are very sensitive to fuel pressure. Low fuel pressure could be a blocked fuel filter - leaking pressure regulator - or a failing fuel pump.
The only way air gets into the fuel system is by a leaking fuel line or o-ring - or - you run the gas tank dry. There should never be air in any fuel injecton system.
Tuesday, December 8th, 2009 AT 11:59 PM