I would like to know what base fuel pressure everyone runs

 

41 psi

 

43 psi

 

42

 

44psi

 

55psi

 

40psi

 

I found if I run any more than 40 psi, I get a wierd studder at injector transition. I will be setting my fuel pressure at around 35-38 psi when I get everything back together. I am using 550 primaries 1680 secondaries in my FD

 

45 psi at idle. Can anyone tell me if I should adjust it? I seem to have that same studder in my FC... 550 primaries and 1600 secondaries, SX fuel pump and regulator, big ss braided lines
~Jeremy

 

45 psi without vacuum hose connected.

 

60 psi

 

38 PSI

 

38PSI wwith 850X1600

 

i agree with silver7, i got same setup 500X1600, i run about 38psi

 

50 psi with 850 primarys and 1300 secondarys.

 

"Very large Secondary injectors might cause stumbles near 4000rpm when they come online"

You have to carefully adjust the aftermarket ECU
to adjust the huge jump from 550
to 1600

 

Well, I'm not sure what to use, & don't tell me to go get help, because you guys ARE my help.

Mods: Stock engine
XS T04E w/1.0 exh A/R
RP/Denso pump
550s/1300s
XS tuned PFC
SX FPR

So, what fuel pressure do you suggest? Vacuum line on or off to set? Car will be street driven, pump gas, 1 bar of boost.

Thanks.

 

Take vacuum line off to set, and set it to 40 psi. You don't need it any higher than that (i.e. your injectors are big enough) so there is no reason to put extra pressure on your fuel pump. Reconnect the vacuum hose after you set the base pressure -- the pressure at idle will drop when you reconnect.

Changing the fuel pressure changes the amount of fuel delivered for a given set of fuel maps. The ECU has no way to know what the fuel pressure is, so it does not account for changes in fuel pressure. If you raise the fuel pressure, you will need to lean out your maps to adjust for that change.

The Factory workshop manual says the base pressure is about 36 psi, but myself and several others have noticed that it is more like 39-40 psi. However, that may be more a function of where we put the sensor than a discrepancy with the manual. I have noticed that the stock regulator does a crappy job of regulating fuel pressure -- my peak pressure is 58 psi when running 13-14 psi of boost (no spikes) and I notice that it jumps around 33-40 under light throttle sometimes, too. I am not sure if the dual-speed fuel pump thing, or the fuel pressure regulator solenoid are responsible for the light throttle fluctuations, but it does seem a little weird. Hopefully an aftermarket regualtor will control the pressure better.

-Max

 

Thanks a lot Max. You've made things a lot clearer.

 

38-40 psi is a good starting point

 

My BASE is 55 psi (vaccum disconnected)... 45 or so at idle. I plan on lowering it when I get it re tuned. For now Its not broke so don't fix it... Wel unless you think 10 mpg is bad

 

I am running 70psi base pressure. (I run up to 20psi boost) Total fuel pressure is up to 90psi.

I got a Bosch Motorsport pump that provides good flow to 120psi with reasonable current draw.

I do this cause my injectors are 12A turbo style and they normally flow 720cc/min @ 40psi ...when I run them at the higher pressure they flow a tested 900cc/min so I got roughly 3600cc/min provides me with enough fuel flow to support 590BHP @ A/F ratio of 10.8:1 with a duty cycle of around 92%

I like to push things to their maximums !

The other benifit of running the higher fuel pressure is that the fuel atomizes better at the higher pressures (mine flows 4200cc/min @ 100psi), so as long as your pump can provide the flow at high pressure I would run it high.

 

A well known mazda racing team member once told me that they try to find really small injectors, run high fuel pressure as well as additional pressure to the fuel cell via some sort of air pump to maximize atomization without the added stress on the JUST the fuel pump.

 

isnt there a way to set it without having the car started?

i was told you could set the base pressure when you repressurize the system by jumpering those 2 connections in the diagnostic box...

please advise...