Fuel pressure regulator

[John B Kobberstad]

Can anyone tell me how long the fuel pressure regulator should hold the pressure in the line (with the pressure up to specs) after the power to the pump is removed?

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[johnzcarz]

I believe there’s usually a check valve in the pump that holds the pressure, it’s usually not the pressure regulator doing that – it’s job is to bleed off excess pressure….at least that’s how it usually works. Although if there is a rupture in the diaphragm it would do what you stated – bleed off pressure once the pump cuts the supply.

The fuel pump is always running when the car is running. In systems where there is a pressure regulator the pump just runs and the regulator maintains the pressure at whatever the spec is. On systems that are ‘returnless’ the pump is controlled by varying it’s duty cycle – which just means it’s pulsed on/off very fast but you would not be able to detect that without a scope or meter that measures duty cycle.

[John B Kobberstad]

Quoted From johnzcarz:

I believe there’s usually a check valve in the pump that holds the pressure, it’s usually not the pressure regulator doing that – it’s job is to bleed off excess pressure….at least that’s how it usually works. Although if there is a rupture in the diaphragm it would do what you stated – bleed off pressure once the pump cuts the supply.

The fuel pump is always running when the car is running. In systems where there is a pressure regulator the pump just runs and the regulator maintains the pressure at whatever the spec is. On systems that are ‘returnless’ the pump is controlled by varying it’s duty cycle – which just means it’s pulsed on/off very fast but you would not be able to detect that without a scope or meter that measures duty cycle.

The pump motor is new and was used in both tests only the regulator/filter was changed on the original pump module. Both regulator/filters controlled the output to 50 psi (spec) only 1 (from the bad Airtex pump module) held the pressure at the output to the line when there was no power applied to the pump. It must be the regulator/filter then that accounts for the pressure remaining at the fuel pump module output to the fuel line.

[johnzcarz]

Yes, sounds like they integrated the ‘check valve’ into that assembly.

[EricTheCarGuy]

I’ve done a video on this in a round about way.
http://www.youtube.com/watch?v=QbzEeWy1b3o

[John B Kobberstad]

Quoted From EricTheCarGuy:

I’ve done a video on this in a round about way.
http://www.youtube.com/watch?v=QbzEeWy1b3o

Thanks Eric, watched 3 of your Airtex videos are there more than 3?

http://www.showmetheparts.com/airtex/ search for E7097M fuel pump to see the type of fuel pump module i’m working on.
If I could post pics here I could show the setup I’m using to test my pumps and pressure regulator/filters.

[John B Kobberstad]

I called Airtex Tech today and found out that supposedly the fuel pressure regulator / filter that is in their fuel pump module assembly for my 1996 Neon( with the plastic tank) has the “check valve” “back flow preventer” what ever it is that maintains the pressure in the line, integrated into the pressure regulator / filter. I also called Standard Motor Products (SMP) Tech and found out that their PR326 pressure regulator / filter does not. In doing my pump checks (before I installed the last fuel pump module) I found that it was the Airtex regulator / filter from my Airtex fuel pump module installed into my original pump module (with the new pump motor) that held the pressure after the power was removed. The regulator / filter that was originally in my original pump module did not hold the pressure with the new pump motor. Some pump motors have the check valve built inside. I guess that is supposed to prevent people like me from trying to rebuild these pump modules and saving $’s. Just thought someone might be interested. Probably not.

[EricTheCarGuy]

Yea it’s not the fuel pressure regulator that holds pressure in the system but the check valve in the fuel pump, this is the reason I posted that video in my original post as that very condition is covered in that video along with an explanation of the check valve and it’s function.

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