What should my Fuel Pressure be???
#1
What should my Fuel Pressure be???
Just wondering if I should bother installing my Kirban FPR. My stock fuel pressure is at 40 with vacuum connected, I can't remember what it is with it disconnected, 42 psi kind of rings a bell. Here's my mods, tell me if you think that I'd be faster if I put it on and turned down my FP.
Mods:
TF street heat upper and lower
70mm TB
75mm pro-m MAF
MAC cold air intake
unequal length headers 1 5/8
off road h pipe 2.5"
Mac catback 2.5"
underdrive pullies
3.90s
custom 3000 rpm torque converter
MSD cap/rotor
blaster TFI coil
taylor wires
NGK plugs
timing at 14 degrees
and I think a few more small things, I can't remember...
Lemme know if my fuel pressure should be any lower, and if I'd gain anything from putting the Kirban on and tuning it. I'm currently running the stocker with a liquid filled gauge.
Mods:
TF street heat upper and lower
70mm TB
75mm pro-m MAF
MAC cold air intake
unequal length headers 1 5/8
off road h pipe 2.5"
Mac catback 2.5"
underdrive pullies
3.90s
custom 3000 rpm torque converter
MSD cap/rotor
blaster TFI coil
taylor wires
NGK plugs
timing at 14 degrees
and I think a few more small things, I can't remember...
Lemme know if my fuel pressure should be any lower, and if I'd gain anything from putting the Kirban on and tuning it. I'm currently running the stocker with a liquid filled gauge.
#3
RE: What should my Fuel Pressure be???
If you don't have any rich/lean failure codes.....it's OK at the setting is at..FYI....
From How Adaptive Control Works By Mike Wesley
From this example, you'll quickly see why an adjustable pressure regulator might not be a good investment of your money. Ford uses a fuel pressure of roughly 39 PSI to rate it's fuel injectors. The fuel regulator operates in conjunction with manifold pressure to keep the delta pressure across the fuel injectors at roughly 39 PSI at all times. In the EEC calibration, there is a number that represents the size of the injectors installed in the engine. This number
represents how much fuel the injector will flow at 39 PSI. The EEC uses this number, along with airflow information to correctly calculate A/F ratio. Based on
the airflow number and its target A/F ratio, the EEC pulses the fuel injector to give just the right amount of fuel to reach its target A/F ratio at any given
Speed/Load point. Now if you were to increase the fuel pressure, the amount of fuel delivered for a given pulsewidth would go up since more fuel will be forced through the injector. As soon as the EEC goes into Closed Loop control, it will 'see' this increased fuel pressure. The reason for this is for any given pulsewidth, the A/F ratio as measured by the oxygen sensor will be richer than what the EEC wanted it to be since now there is more fuel delivered with the same pulsewidth. The EEC will calculate the difference from what it wanted and what it got and update the Adaptive table with a 'correction factor' and use this correction factor to reduce the injector pulsewidth the next time the injector fires. Eventually what happens is the EEC is able to 'dial out' the extra fuel that was added by increasing the fuel pressure. Now you can probably see why raising the fuel pressure is only a temporary 'fix' for a lean problem. Soon you will be right back where you started from. The EEC is continuously updating the Adaptive table anytime it is in Closed Loop.
represents how much fuel the injector will flow at 39 PSI. The EEC uses this number, along with airflow information to correctly calculate A/F ratio. Based on
the airflow number and its target A/F ratio, the EEC pulses the fuel injector to give just the right amount of fuel to reach its target A/F ratio at any given
Speed/Load point. Now if you were to increase the fuel pressure, the amount of fuel delivered for a given pulsewidth would go up since more fuel will be forced through the injector. As soon as the EEC goes into Closed Loop control, it will 'see' this increased fuel pressure. The reason for this is for any given pulsewidth, the A/F ratio as measured by the oxygen sensor will be richer than what the EEC wanted it to be since now there is more fuel delivered with the same pulsewidth. The EEC will calculate the difference from what it wanted and what it got and update the Adaptive table with a 'correction factor' and use this correction factor to reduce the injector pulsewidth the next time the injector fires. Eventually what happens is the EEC is able to 'dial out' the extra fuel that was added by increasing the fuel pressure. Now you can probably see why raising the fuel pressure is only a temporary 'fix' for a lean problem. Soon you will be right back where you started from. The EEC is continuously updating the Adaptive table anytime it is in Closed Loop.
#4
RE: What should my Fuel Pressure be???
Your fuel pressure should be 39-42 psi with the vacume line OFF, then at idle, when you put the vacume line back on, it should drop to around 35 psi. the injectors are designed to operate at 39-42 psi. if you run it less, you may lean out your car at wot. if you make it more, you might make it run rich, which is beter than running lean, but you still lose power either way. stay around 40 and you'll be good.
#7
RE: What should my Fuel Pressure be???
Yeah, I have no need to upgrade my injectors, I don't plan on doing heads or F/I for a long long time, I'm going to max out my suspension now and see how low I can get with the minor motor mods, the big stall, gears, tires and a full aftermarket suspension.
#10
RE: What should my Fuel Pressure be???
Oh sweet, thanks Joel, I kinda figured that it was something like that, but wasn't sure. Kinda like the TPS, as long as it's between I think .66v and .99 computer takes care of it at idle.