FPR without vacumn hose

[NeilW]

Evening guys,
I'm chasing a top-end (lack of) power problem. I've been checking the vacumn hoses and as an experiment I disconnected the vacumn hose from the fuel pressure regulator. There was no difference when I then drove the car. My understanding is that the vacumn pulls a diaphragm, which then increases fuel pressure and enrichens the mixture. There was definately vacumn at the end of the hose using the old finger test method. So my question is, should I have noticed a difference driving the car without the vac line attached? And if so, does this point to a faulty FPR? This is on my S not the turbo.

 

[Indi9xx]

a 944lux, S, S2 or turbo fuel pressure regulator all work the same way.

Give them a vacuum to the vacuum take off and they will reduce the fuel pressure, add air pressure and they will increase fuel pressure.

So, in all models at idle they will cause a lower fuel pressure (not very much lower) which means that the less you open the throttle the lower the fuel pressure and so less enrichment.

On a normally aspirated engine this means that at idle they give less fuel (good for emissions) but as soon as you crack the throttle open they will increase fuel pressure a little to give an additional amount of enrichment over what the DME will give.

On a turbo charged engine, they will also increase fuel pressure even further the more boost you produce.

 

[NeilW]

Thanks Jon.