The V8 Owners Forum -

Hi
Need help I am running a 3.9'efi disco engine in my stag
Running a bosch 070 external fuel pump an rpi boost fpr
And have got a fuel pressure gauge set the fuel pressure at 2.0 bar which rises to 2.5 bar when I accelerate
Have I got the right set up ie fuel pump set pressure or is there not enough flow the engine misfire,s under load
Thx

The nominal pressure on a flapper is 36psi which is 2.5 bar - checked vacuum disconnected, so the maximum. But when I had an FSE rising rate, it didn't seem to be right, so raised it to 38 psi. Not sure if the hotwire is the same. But if the EFI mapping is correct there shouldn't be a need to use such a crude way to increase the fuelling.

hotwire is 3 bar iirc (tested with engine off and fuel pump running)


actually its 2.5 bar:
http://www.britishv8.org/Articles/Rover-14CUX-EFI.htm

but you set the pressure with engine off (atmospheric pressure) and force the pump on (bypass the relay)

Just a comment Setting the pressure with the engine stopped may be fine on a brand new vehicle. But with an older one, where there will likely be more voltage drop - and possibly a tired pump - I'd have thought engine running with the voltage that gives a better way?

DaveEFI wrote: ↑

Wed Jul 17, 2019 12:04 pm

Just a comment Setting the pressure with the engine stopped may be fine on a brand new vehicle. But with an older one, where there will likely be more voltage drop - and possibly a tired pump - I'd have thought engine running with the voltage that gives a better way?

With the engine off, you will be setting the pressure as a worse case scenario (lowest voltage) - with the engine running and hence higher voltage, the regulator will do it's job and regulate it to 2.5 bar - no?
Also my understanding is that it's a static pressure - with no flow across through injectors.

IMO set base pressure ( if adjustable of course ) to desired pressure, vac disconnected and engine running.

Lucas Hotwire stock pressure is 2.5 BAR if your using just 2 BAR that may well be your misfire from an over lean AFR (dangerous for the motor)