FPR - Before or after injector?

WhiteFox · May 8th, 2003, 06:03 PM

Simple question, I hope.
Does the fuel pressure regulator go in line before or after the fuel's fed through the injector? Would there be a pressure difference if it was reversed?

(The swap is so close to being complete.. Yes, after SO damn long..)

fastpakr · May 8th, 2003, 06:18 PM

Most of the ones I've looked at had the FPR on the back side of the rail. It shouldn't really matter where it's put as long as overpressure in the rail is bled off.

WhiteFox · May 8th, 2003, 06:34 PM

Thanks for the info

hybrid DET · May 8th, 2003, 07:16 PM

after the injector

hybrid DET · May 8th, 2003, 07:17 PM

Quote:

Originally posted by fastpakr
Most of the ones I've looked at had the FPR on the back side of the rail. It shouldn't really matter where it's put as long as overpressure in the rail is bled off.

car will run like ass with the FPR before the injector

LittlebittaContact · May 8th, 2003, 07:33 PM

yea, the way it works is the fuel pump can pump way more then the car needs, so it pressureizes the whole line to whatever its maximum output is and after the injector(s) the regulator lets the extra pressure go.

fastpakr · May 8th, 2003, 10:07 PM

Quote:

Originally posted by hybrid DET
car will run like ass with the FPR before the injector

I believe you, but can you explain why? Now that you mention it, I remember somebody else telling me that in the past but they didn't explain what the reason was.

Myetball · May 8th, 2003, 10:25 PM

Think of it this way, the pressure regulator maintains a constant pressure behind it and allows excess pressure to flow past. Put in line after the injectors it is maintaining pressure between the pump and regulator, thus the injectors receive a constant pressure. The excess pressure is bled off and returned to the fuel tank.

If you put the regulator before the injectors, the regulated pressure would still be maintained between the pump and regulator. The injectors would only be receiving the bleed off that exceeded the regulators set maximum. If your pump was putting out 17psi and the regulator was set to 14psi, the injectors would only be getting 3psi.

Does this make any sense?

fastpakr · May 8th, 2003, 10:47 PM

Yeah, that actually made perfect sense. I'm not sure why the logic of it didn't hit me before. Thanks.

WhiteFox · May 13th, 2003, 04:11 AM

Okay, I got things straightened out now, I think..

The FPR is a one-way valve, bleeding off excess line pressure.

With this in mind, I've got an odd idea (read: F*cked up), and hope that someone could give thumbs up or down on it.

I have no replacement for the FPR on my current TB, so it's going to have to stay put. At first, I completely overlooked how the FPR's worked, so I planned on putting a new one in-line (for lower pressure). I see the error of my original plan now.

Here's the new fuel plan..

..+=============+===============< < < pump
..||......................||
..||......................||....FPR (2)
.(o)..injector..........+=== )> ===+
..||.......................................||
..||.......................................||
..+==== )> ================+=====> > > fuel return
..........FPR (1)

FPR1 is high pressure and FPR2 is low. This routing should operate the same way as having just FPR2 installed in place of FPR1. Any insight? Suggestions?

blownb310 · May 13th, 2003, 05:56 PM

Quote:

Originally posted by WhiteFox
(The swap is so close to being complete.. Yes, after SO damn long..)

**** Whitefox, glad to hear you haven't given up. Can you bring us up to date on this project? Is it rich or lean?

WhiteFox · May 14th, 2003, 02:53 AM

At current, with only the GA16 FPR that's on it, it runs rich. It should be running perfect after I install the original E16 FPR into the lines (There's no way I can remove the FPR that's on the TB). At worst it could be a bit lean, in which I will try removing the vaccume line. That should add a bit more pressure.. one way or another thing's hopefully will work out.