The V8 Owners Forum -

i have fitted a non standard fuel pressure regulator as my origanal was giving me trouble, new one has a gauge, what presure should the system be at? when running now its at about 20psi, an was about 35 ish when primeing.

its a flapper efi engine, but is running an emerald ECU.


Ralph

Ralphh85 wrote:i have fitted a non standard fuel pressure regulator as my origanal was giving me trouble, new one has a gauge, what presure should the system be at? when running now its at about 20psi, an was about 35 ish when primeing.

its a flapper efi engine, but is running an emerald ECU.


Ralph

Flapper is 36 psi vacuum disconnected. Drops to about 28 psi at idle with vacuum connected. But the second reading will depend on cam, ignition timing, etc.

ideal thanks for info, didnt realise vacuum had to be disconnected, will check again later.


Ralph

I believe the reason being that high "vacuum" will suck fuel from injectors and hence you need to compensate by lowering the fuel pressure. I never quite worked out why the ECU doesn't just lower the duty cycle to compensate for this as MAP systems measure the "vacuum" by definition!

i think its better having the pressure varying, if nothing else it makes the map more level for each load site which makes it easyer to pick spikes etc.


Ralph

If you're running a custom ecu then the actual fuel pressure isn't to important. As long as you have enough to fuel pressure for the required power level.
you will need to tell the ecu what the fuel pressure is and also the fuel injector flow rate for it to work out the required fuel.
You can do an easy calculation to estimate your fuel pressure you'll need to reach your expected power. Just Google fuel injector flow calculation.
Is you're new fuel reg a rising rate type? these aren't ideal for custom ecu's. Only really a bodge for standard ecu's to increase the fuel a little.
Tom