s70-What is the difference?FPR and fuel press.damper

deeperblue · Post by **deeperblue** » 04 May 2014, 13:13

hi I want to learn what is the differance of fuel pressure resgulator and fuel pressure damper?thanks

Post by **Ozark Lee** » 04 May 2014, 20:03

If I'm not mistaken the fuel pressure regulator is used on a system with a fuel return line and the damper regulates the pressure on the single ended system that doesn't have a fuel return line. The regulator regulates pressure on the way out of the fuel rail while the damper regulates pressure on the way into the fuel rail.

...Lee

Post by **cn90** » 04 May 2014, 20:26

This is the way I understand it...

The fuel pressure regulator and the fuel damper are completely different in function and form.

The FPR has a larger body and a vacuum line to regulate the fuel system pressure by vacuum load, let's say the engineers design the fuel pressure to be around 42 psi +/- a bit. So you may see anywhere between 40-44 psi or so.

So let's say fuel pressure is constant at 42 psi, once the fuel injectors open, it drops down a bit, then back up when more fuel flows in. If you hook a gauge to it, you will see pressure as a sine wave.

The fuel damper is much smaller and only dampens the fuel pulses to the injectors. So basically the damper makes the amplitude of the sine waves smaller.

Anyway, this is the way I understand it, I may be wrong though.

Post by **jimmy57** » 05 May 2014, 06:11

CN90 has it right. FPR is used on both of these but it is remote on the systems using the damper. The damper went invisible in 2005-2006. The damper is a flattened seal tube inside the fuel rail as the single point damper was not effective fully over the length of the fuel rail.
FPR goes away beginning in 2003 and fully integrated on all US engines in 2007, when the fuel pressure sensor is fitted. The FPS is supplying ECM with pressure value and ECM in turn is controlling pump via the PEM/FPM to run pump at the speed that gives desired fuel pressure.

Post by **abscate** » 05 May 2014, 06:15

I don't think I have an FPR on my ME 7 1999, fwiw. It's not on the vacuum diagram and I have a single fuel line up to the rail.

Post by **misha** » 05 May 2014, 17:57

Cn90 explained it properly.

deeperblue · Post by **deeperblue** » 05 May 2014, 23:14

ok my friends many thanks....

Post by **jimmy57** » 06 May 2014, 05:49

abscate wrote:I don't think I have an FPR on my ME 7 1999, fwiw. It's not on the vacuum diagram and I have a single fuel line up to the rail.

It's built into fuel line back by tank or is integrated into the top of the fuel pump/sending unit from 1999 until fuel pressure regulation goes to fuel pressure sensor-ECM-PEM system in mid 2000's.
When the fuel pressure went to a fixed pressure with no manifold pressure reference there was no reason for it to be up front anywhere.

MMT51 · Post by **MMT51** » 06 May 2014, 06:45

The fuel pressure in my 2000 S70 GLT seems high, 50psi with key in ignition, and 56psi at idle. Current mileage is 144K, I've owned it since 80K. I don't know if the fuel pump was replaced by previous owner.
Is this anything to be concerned about?

No problems with the car except a wavering idle, 835-870rpm, that I've been trying to cure for the past 18 months as I renew the car:
https://www.matthewsvolvosite.com/forums ... =1&t=54150

Thanks for any advice.

Peter

Post by **misha** » 06 May 2014, 14:30

MMT51 wrote:The fuel pressure in my 2000 S70 GLT seems high, 50psi with key in ignition, and 56psi at idle...

I think that it's correct fuel pressure for '99-'00 models.In fact,i think that the newer models from '01 and on also have the same fuel pressure.Could be wrong but i'm pretty sure about this.

Constant rpm change at idle (unstable idle) on your car could be related to notorious ETM module failure.