what's the best place to mount a fuel pressure gauge?

between pump and regulator or after the regulator?
Andy

Mine is mounted on the Regulator on the side the feeds the carbs...
So its measuring the pressure after its been regulated

QUOTE (SirAndy @ Dec 28 2005, 12:32 PM)

what's the best place to mount a fuel pressure gauge? between pump and regulator or after the regulator? Andy

Well, if you mount it after the regulator, you're gonna get a reading that is utterly meaningless, because any regulation it does happens upstream. I use the test port on the injector manifold. If you're not speaking of an EFI T4 motor, you'll have to find out wiere the test port is on your particular engine. The Cap'n

If your regulator is for FI, (has a return line) the pressure you want to measure is before the regulator. If it's for a carb (no return line) then the pressure you want to measure is after the regulator. (some carb regulators use a return line, in which case you'd measure before)

Whatever the case, measure the side of the regulator that's feeding fuel to the engine.

QUOTE (Cap'n Krusty @ Dec 28 2005, 12:36 PM)

Well, if you mount it after the regulator, you're gonna get a reading that is utterly meaningless, because any regulation it does happens upstream. I use the test port on the injector manifold. If you're not speaking of an EFI T4 motor, you'll have to find out wiere the test port is on your particular engine.

yes, EFI T4 ...

so, between the pump and regulator it is.
Andy

Carb setups CAN have a return line...

Normally, it's set up: tank -> pump -> injectors -> regulator -> return. Regulator open means fuel gets dumped to the return line (pressure goes down), regulator closed means fuel doesn't go down the return line (pressure goes up). In this case, you measure fuel pressure anywhere between the pump and the regulator.

It's also possible to set it up: tank -> pump -> regulator -> injectors with a split at the regulator so it can "select" whether to dump the fuel down to the injectors or down the return path. In this case, you should measure between the regulator and the injectors, as this is the pressure actually being used by the injectors. The pressure *should* be the same as the pressure between the pump and the regulator.

Finally, you can dead head the thing and have no return at all by doing pump -> regulator -> injectors, but you really have to control the pump somehow (PWM is usually used to vary the pump volume), and modern "returnless" injection systems do this. Sometimes, such "returnless" systems use a tank-mounted pump and regulator, so the "return" is still there, but it's all inside the tank, so there's no return "line". You'd measure the fuel pressure here anywhere at all, it should be the same everywhere.

You can swap "carbs" for "injectors" and it all still works out. You usually see option 3 on most carb setups, and option 1 on most aftermarket injection setups.

Andy,

make sure the guage is not mounted on the motor.
only on the chassis...

I've seen the fires that result from mounting on the motor

(more vibration> cracked fittings> big flash with smoke> bad!)

regarding the return line debate for carbs...
F'it.... I'm out

brant

QUOTE (lapuwali @ Dec 28 2005, 02:32 PM)

Carb setups CAN have a return line...

I firmly believe that ALL fuel systems should have a return line but that's just me.
-Ben M.