whats the difference between idle fuel pressure and static fuel pressure.

is static when you are at a constant speed?



-------jezreel

idle = pressure in vacuum at idle (somehow, mine is around 12 psi of fuel with the 415's, the only fuel pressure that produces a good idle, stock injectors should idle around 45 psi of fuel)

static = pressure at 0 psi of boost (mine is about 25 psi of fuel with the 415's. stock injectors should be about 52-55 psi of fuel)

2016 WRX STi Limited (current)
2001 A4 1.8tqms (donated)
1991 GVR4 #1933 (sold)
old.dsmregistry.com/detail.php?carid=218 (dismantled)

how can you tell what the readings are with out a boost gauge?

i have a dyno tune digital fuel pressure gauge and i am beginning to think theres something wrong with it. like when i adjust the sfmu to make the fuel pressure go higher at park, it will go to 45 psi. then when i cruise it drops to 39 psi, at stops, it goes to 41 psi. this is without a turbo, i am on stock injectors.

is this normal?

-------jezreel

how can you tell what the readings are with out a boost gauge?

i have a dyno tune digital fuel pressure gauge and i am beginning to think theres something wrong with it. like when i adjust the sfmu to make the fuel pressure go higher at park, it will go to 45 psi. then when i cruise it drops to 39 psi, at stops, it goes to 41 psi. this is without a turbo, i am on stock injectors.

is this normal?

-------jezreel

bumpo
-------jezreel

Idle fuel pressure is idle at full idle vacuum. The idle fuel pressure will be less than the static.

Static fuel pressure is the fuel pressure with the regulator's vacuum signal unplugged - in a NA car, the maximum fuel pressure you'd see. In a boosted car, it's the fuel pressure while at atmospheric pressure (no vacuum, no boost).

You should always adjust fuel pressure by adjusting the static. Do this by unplugging your regulator's vacuum souce, capping it, and adjusting your fuel pressure from there.

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'95 Eclipse TurboGS (garage deco)
'95 TSi AWD (restoring a survivor)
'97 Talon ESi-T (poor impulse control)
'99 Eclipse RS-T (daily beater)
'13 Evo X (mostly stock)
'17 Sienna (Middle Aged Dad Mobile)



Factory Service Manuals: http://nawdu.de/files/

You can get the SFMU to hold at the static fuel pressure by disconnecting the vacuum line to it. No vacuum = 0 psi boost.

To set the idle fuel pressure - keep the vacuum line hooked up.

The difference in fuel pressure as you're cruising and stoping are purposefull even without boosting. When the air pressure in the intake manifold is lower its easier to push gas out of an injector - so the fpr lowers the fuel pressure to compensate. When the pressure in the intake manifold is higher its harder to push gas out of an injector - so the fpr raises the fuel pressure to compensate. If you don't have a turbo then you shouldn't hit static fuel pressure while you're driving, because an N/A engine's intake manifold is always under vacuum.


95 Eclipse RS : 5 speed
15.901 @ 88.34mph
Jeep TB writeup - http://www.dimensia.com:81/jimbo/JeepTBfor2gnt.html

aha. i have seen the light jim. whew, i thought i had to drop another 200 for a fuel guage. i think i'm gonna hook up the vacuum wires to the sfmu and get the boost gauge ready.
-------jezreel