fuel pressure required
- Thread starter raph130
- Start date
your stock fuel pressure regulator runs anywhere between 39psi to 41psi...with stock injectors...with bigger injectors you still have to run at the same psi because your MAF is still calibrated for that specific injector...running less or more will influence the way your MAF delivers the proper air to fuel ratio...many argue that an adjustable fuel pressure regulator is pointless...if you are going to run at the stock fuel pressure...besides your computer is still programed to run at 19lb injector so you have to take that into consideration...that's where tuning comes into play...but I'm not a tuner so I can't help you...running at stock fuel pressure with bigger injectors is actually what is recommened...if you have to run more than stock fuel pressure...than you need a bigger injector.
i would worry about the quality of the spray pattern with too low of a pressure.
remember that the puter will adapt (~+/- 25%). if the puter realizes you are running rich or lean, it will trim the injector pulsewidth to accomodate this and get back to stoich.
if you cant support a larger injector at near the stock fuel pressure setting, i would wonder why one would have gone with 24's (there could be a very good reason that i simply missed, so please dont take offense).
my two cents. good luck.
remember that the puter will adapt (~+/- 25%). if the puter realizes you are running rich or lean, it will trim the injector pulsewidth to accomodate this and get back to stoich.
if you cant support a larger injector at near the stock fuel pressure setting, i would wonder why one would have gone with 24's (there could be a very good reason that i simply missed, so please dont take offense).
my two cents. good luck.
Use the SOP meter...
Get one of your buddies to ride along with you. Find a level stretch of road where you can do some testing. Don't choose a speed range that will make you shift gears, the shift quality & speed will affect your results. Use 2nd or 3rd gear and do a run from 2000 RPM to 5800 RPM. Call out the RPM as it increases and have you buddy record it and the elapsed time. If you have one of those cheap digital watches like I do, a stop watch is built in. Start the fuel pressure at 36 PSI, vacuum off and make a run. Turn it up to 37 and make another. Be sure to reconnect the vacuum every time you set the pressure. Keep turning up the pressure and making runs until you notice a drop off in time. If your bud was careful to record the results, you'll have a nice chart to use to find the optimum pressure.
Get one of your buddies to ride along with you. Find a level stretch of road where you can do some testing. Don't choose a speed range that will make you shift gears, the shift quality & speed will affect your results. Use 2nd or 3rd gear and do a run from 2000 RPM to 5800 RPM. Call out the RPM as it increases and have you buddy record it and the elapsed time. If you have one of those cheap digital watches like I do, a stop watch is built in. Start the fuel pressure at 36 PSI, vacuum off and make a run. Turn it up to 37 and make another. Be sure to reconnect the vacuum every time you set the pressure. Keep turning up the pressure and making runs until you notice a drop off in time. If your bud was careful to record the results, you'll have a nice chart to use to find the optimum pressure.
raph130 said:
I run 30lb injectors at 39psi and it runs perfect as far as I can tell...no hesitating or nothing...an occasional idle surge but that is normal and doesn't effect performance...I pulled the plugs out and they look good...as long as you have a MAF calibrated for the injectors you can run 24's or 30's...
Michael Yount
Mustang Master
raph - if the maf is calibrated correctly, it "adjusts" for the larger injectors. The maf and the ecu are both expecting to see stock fuel pressure - 38-40 psi measured at idle with the engine warm and the vacuum line off the regulator and capped.
The ecu has adaptive strategies - it will adjust things to try and keep the a/f ratio in a range that's designed for best emissions. You can increase or decrease the fuel pressure - but the computer over time will simply decrease or increase the injector pulse width to get the a/f ratio back where it's supposed to be. You turn the pressure up - it simply holds the injector open for less time; you turn it down, it simply holds the injector open for longer. And, it will, over time, also make adjustments to the wot tables as well.
So, as long as your maf is calibrated for the 24# injectors, leave the fuel pressure alone. You're not gonna accomplish much of anything in the long run playing with it.
The ecu has adaptive strategies - it will adjust things to try and keep the a/f ratio in a range that's designed for best emissions. You can increase or decrease the fuel pressure - but the computer over time will simply decrease or increase the injector pulse width to get the a/f ratio back where it's supposed to be. You turn the pressure up - it simply holds the injector open for less time; you turn it down, it simply holds the injector open for longer. And, it will, over time, also make adjustments to the wot tables as well.
So, as long as your maf is calibrated for the 24# injectors, leave the fuel pressure alone. You're not gonna accomplish much of anything in the long run playing with it.
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