Fuel pressure testing

[Andy335Touring]

My fuel pressure regulator (FPR) is rated at 3 BAR fuel pressure but is that supposed to be at tick over or wide open throttle (WOT) ?

Where can i buy a suitable gauge from ?

When i get a gauge whats the best way to use it to make sure the FPR is working properly ?

I'm guessing i should test the fuel pressure with the engine running at tick over with and with out the vacuum line attached to simulate WOT or no vacuum signal to show the change of fuel pressure ?

[kam-325i]

Depends which side of the FPR you want to gauge.

Two setups:
1, Fit gauge to the fuel feed line before FPR, This will read pressure deliverd by pump.
2, Fit gauge between FPR AND Fuel rail to gauge FPR.

Second one is a bit tricky....

[Andy335Touring]

The way that i see it is that the fuel rail and the feed pipe should be at the same pressure and that the FPR dumps any extra fuel out by the return pipe, kind of like an over flow.

So if i have got it right i should be able to put a T-piece into the feed pipe and connect the gauge from the T ?

The return pipe shouldn't be pressurised because theres nothing in theory to restrict its travel from the FPR to the tank.

[Templ8e30]

The way that i see it is that the fuel rail and the feed pipe should be at the same pressure and that the FPR dumps any extra fuel out by the return pipe, kind of like an over flow.

So if i have got it right i should be able to put a T-piece into the feed pipe and connect the gauge from the T ?

The return pipe shouldn't be pressurised because theres nothing in theory to restrict its travel from the FPR to the tank.

100% correct mate.

The FPR should be 3.0bar with WOT and can be simulated as you mentioned by disconnecting the vac feed pipe.

Note that without the engine running this figure will be different, I don't know why but when I checked mine I was getting 3.2 bar without the engine running but 3.0 bar with it running . The Vacuum connection on the inlet manifold will need blocking off too (thumb over the end works), good excuse to get the missus involved .

Cheers,

Iain T

[E30Adam]

2, Fit gauge between FPR AND Fuel rail to gauge FPR.

Second one is a bit tricky....

You can't do this unless you use a remote FPR though as the regulator sits directly into the fuel rail.

[TVRTASMIN]

A decent fuel pressure testing kit will cost around Ԛ£250 anyway. There are cheaper ones available but only for low pressure carb setups.
Cheaper to buy a new regulator unless you are intending using a gauge on a regular basis.

[Turbo-Brown]

My understanding of it was that the signal line to the FPR was to enable it to keep the pressure at 3bar above manifold pressure.

Seems to make sense(ish) to me anyway

[Andy335Touring]

The way that i see it is that the fuel rail and the feed pipe should be at the same pressure and that the FPR dumps any extra fuel out by the return pipe, kind of like an over flow.

So if i have got it right i should be able to put a T-piece into the feed pipe and connect the gauge from the T ?

The return pipe shouldn't be pressurised because theres nothing in theory to restrict its travel from the FPR to the tank.

100% correct mate.

The FPR should be 3.0bar with WOT and can be simulated as you mentioned by disconnecting the vac feed pipe.

Note that without the engine running this figure will be different, I don't know why but when I checked mine I was getting 3.2 bar without the engine running but 3.0 bar with it running . The Vacuum connection on the inlet manifold will need blocking off too (thumb over the end works), good excuse to get the missus involved .

Cheers,

Iain T

Thanks for the info guys

So if it's supposed to be 3 BAR at simulated WOT what should it be at tick over with the vacuum pipe conneced ?

You have a good point about just buying a new FPR rather than forking out for a gauge.

I've just thought of another kind of indirect way to test the FPR. I've just bought a WBO2 sensor so i could check the mixture at tick over with and with out the vacuum line connected, if the mixture doesn't change then the FPR is knackered ?