nik968

Hi all! Question: if I pull the vacuum line from the fuel pressure regulator whilst the engine is idling should this have an effect on the idling? Just tried this today ; especially if I cap the loose vacuum line, pulling of the line from FPR does not seem to have any effect on the engine idling. Thinking is there something fishy with my regulator?
Br, -Nik

chudson

The regulator is designed to increase fuel pressure as manifold vacuum decreases. Do not concern yourself with whether or not the idle speed or quality changes. To determine if the regulator is functioning correctly, you will need to attach a fuel pressure gauge with a minimum of a 5 bar scale to the sample port (the big nut in the fuel rail - careful there is a ball under the nut). You can also test with an in-line adapter installed between the fuel inlet hose and the fuel rail. Then you check the pressure with and without vacuum applied. Specs are in the WSM. I hope this helps.

Cliff

nik968

Great, thanks. I will find a fuel pressure gauge somewhere and see what that tells.

Zirconocene

If you want to go down a rabbit hole, these are called rising rate dampers. I don't think that they're as critical on the 968 as they were on the 944 (which were batch fired and injected), but the concept seems to have carried over as I don't think that there's a downside to them in this application.

Cheers

Jfrahm

The regulator actually reduces fuel pressure to match engine vacuum so the shot of fuel stays the same per injector pulse width independent of engine vacuum. Otherwise at higher engine vacuum the engine would pull extra fuel through the injector.
The vacuum would also tidy up any fuel that slips past the diaphragm and this probably happens. Without the vacuum fuel might eventually fill the "dry" chamber and lock it up. It also provides a way to manage any fuel that leaks when the diaphragm fails.

Rising rate regulators are used for boosted applications to provide extra fuel under boost. Our stock regulators are not of this type. They would give you you, for example, 50psi normally but 65 psi under 5lb of boost.

-Joel.