Fuel pressure regulator vs. pressure gauge?

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sirhk100

Racer
Feb 24, 2003
16,421
266
83
Las Vegas
I currently have a fuel pressure gauge in my dash and the sending unit is plumbed into my return line. Currently I'm also running the factory pressure regulator on the fuel rail of the LQ9/LS2 that I've got in my F150. Because of the motor work I've done with this engine I need to block off that stock regulator and plumb in a adjustable regulator. I bought a Aeromotive one last night. My question though...

Since i already have a gauge in the dash I'm not going to run one physically on the regulator itself. So in this setup... For the gauge to work accurately, does it matter if I put the regulator between in the return line between the engine and the gauge sending unit? Or does it matter if i put the regulator between the sending unit and the tank?

Basically does the regulator position in the return line in relation to the gauge sending unit affect the reading on the gauge?
 

84projectford

Senior Member
Sep 8, 2010
1,308
748
113
Phoenix Az
how are you seeing any fuel pressure at all on the return side after the reg?

just plumb the gauge into the port the gauge would be going into on the regulator. that will give you pressure at the injectors
 

04yfzkid

I are smarts
Mar 21, 2007
33,498
376
83
Flagstaff, AZ
Everyone has their own way of doing it. I like to plumb from my pumps into the rail, cross over to the other rail, and run the return on the "outlet" of the other rail. If it's a high hp car with on ethanol I Y into the rails and Y out of the rails to the regulator. In my head that keeps the fuel pressure at the injectors constant even while they are opening.

If you put the regulator before the rails then it is essentially a returnless or dead head set up. I've seen a lot of people do this and have it work successfully. I've also helped work on a couple cars that would have hot start issues. The fuel and any air in the lines would heat up and the car wouldn't start until it cooled off. Not sure if they just plumbed everything wrong, a faulty regulator, or what the issue was.

The fuel pressur sensor should be either on the FPR or somewhere on the pressure side. The return side is bleeding off excessive pressure and is not a measurement of what the fuel pressure going to the rails is. If the sensor is 1/8" NPT just screw it into the regulator. It should come shipped with that port having a plug in it.
 
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sirhk100

Racer
Feb 24, 2003
16,421
266
83
Las Vegas
how are you seeing any fuel pressure at all on the return side after the reg?

just plumb the gauge into the port the gauge would be going into on the regulator. that will give you pressure at the injectors
Honestly, it's been so long since the truck ran, I don't even remember... I guess I need to crawl under and verify which line the sending unit is on. I honestly didn't even look, I just assumed it was on the return line for some reason. Guess I should've verified my current setup 100% before posting this instead of assuming off memory! LOL

I just bought the regulator last night and it's on my mind as something to deal with here in the next week before doing the first fire on this new motor.
 

sirhk100

Racer
Feb 24, 2003
16,421
266
83
Las Vegas
Everyone has their own way of doing it. I like to plumb from my pumps into the rail, cross over to the other rail, and run the return on the "outlet" of the other rail. If it's a high hp car with on ethanol I Y into the rails and Y out of the rails to the regulator. In my head that keeps the fuel pressure at the injectors constant even while they are opening.

If you put the regulator before the rails then it is essentially a returnless or dead head set up. I've seen a lot of people do this and have it work successfully. I've also helped work on a couple cars that would have hot start issues. The fuel and any air in the lines would heat up and the car wouldn't start until it cooled off. Not sure if they just plumbed everything wrong, a faulty regulator, or what the issue was.

The fuel pressur sensor should be either on the FPR or somewhere on the pressure side. The return side is bleeding off excessive pressure and is not a measurement of what the fuel pressure going to the rails is. If the sensor is 1/8" NPT just screw it into the regulator. It should come shipped with that port having a plug in it.
I'm using the factory fuel rail setup and trying not to spend money if not 100% needed. I know guys with MUCH more power are getting away with the factory fuel rails on these motors so I'm trying to as well. That said I'm 99% certain the supply and return on factory are coming off the same side (drvr) so plumbing it the way you mention above isn't really an option I don't think without replacing the rails.

Was planning to do it on the return to avoid that dead head setup.

As I mentioned above I need to double check, maybe the pressure sensor actually is on the supply side... I'm going off memory honestly and as mentioned above I definitely should've double checked that before posting. LOL, my bad!!! I'll double check some stuff tonight while I'm under it tossing the transmission in and then jump back on here tomorrow if needed.

Either way though, sounds like get my pressure sensor on the supply side, get my regulator on the return side and I should be golden if I'm understanding everything correctly.
 

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