fuel pressure education

DirtKing · 03-18-2002, 09:04 PM

I need one. What effect does lowering or raising fuel pressure have on a set of injectors?? I understand the whole boost/vacuum reference issue. I also understand the eec iv will begin to compensate for altered FP under closed loop operations. All things equal does raising FP on a 19 lb injector 5lb turn it into a 24. How about the reverse? Any thought would be appreciated. I'm curious why ford picked the static FP that they did?

LOWKEY · 03-18-2002, 09:25 PM

There is a formula for calculating injector size @ different fp's in the link below.

http://www.pro-flow.com/mustmath.htm

http://www.pro-flow.com/t-car.html

ArtMan · 03-18-2002, 10:15 PM

I often wondered why the stock fuel pressure is 39 psi too. I'll bet it has something to do with the injector design rather than the fuel pump design. In any case, that's what Ford has decided all stock EECs will assume is present at the injectors. When you increase fuel pressure through the use of an adjustable fuel pressure regulator more fuel flow occurs. The computer doesn't detect this during Wide Open Throttle operation, because the O2 sensors are shut off.

This extra fuel can produce extra horsepower if accompanied by extra air. But there's a limit. Increasing fuel pressure excessively degrades the spray pattern of the injector and poor fuel delivery can occur. So, I'm not sure if you can effectively turn 19# injectors into 24s. The relationship between pressure and flow is not linear.

Generally, if you feel the need for 24# injectors you should just upgrade, because you will likely do other mods that require them. Fooling the computer just goes so far.

DirtKing · 03-18-2002, 11:34 PM

thanks for the input...I'm not running the eek 4, but I'm interested in the theory behind it and fuel injection in general...anyone else??

DirtKing · 03-18-2002, 11:52 PM

by the way, excellent link lowkey....interesting to see that it takes an aweful lot of pressure to increase flow.

exgmguy · 03-18-2002, 11:57 PM

When I hit the spray my injectors see a tad under 100 psi.

They will go static if ran at that pressure for more than a 1/4 mile at a time.

RED92LX50 · 03-19-2002, 02:17 PM

I have seen mentioned on other posts that the computer (over time - not sure how long) will adjust to the modified fuel pressure, effectively resetting it??? Is this true?

Basically, it was stated that you could adjust your FP at the dyno to get peak HP, but after a while the computer would adjust to offset your changes (effectively cancelling your FP adjustment). Any truth to any of this?

FdMust88 · 03-19-2002, 02:40 PM

Although the site:

http://www.howstuffworks.com/fuel-injection.htm

may not directly answer your question(s), I felt as though there is enough valuable information listed on the site worth sharing with others.. They have some pretty cool stuff all throughout the site; check it out...

juiceman · 03-19-2002, 10:40 PM

raising fuel pressure will in turn raise injector flow rate and vise versa. ford likely picked that stock pressure based on those injectors flowing 19 lbs. hr. at said press. for info and some formulas that will help and explain more go to www.msdignition.com click on fuel management

ArtMan · 03-20-2002, 04:01 PM

Red,

I don't think so. The '87 to '95 Stangs did not adjust fuel pressure through the EEC. As noted above the EEC did re-adjust pulse width during closed loop operation, but that's not what we're talking about here. WOT only.

Not sure about '96 and newer, though.

03-18-2002, 09:04 PM	#1
DirtKing Registered Member Join Date: Feb 1999 Location: brooklyn center,mn,USA Posts: 169	fuel pressure education I need one. What effect does lowering or raising fuel pressure have on a set of injectors?? I understand the whole boost/vacuum reference issue. I also understand the eec iv will begin to compensate for altered FP under closed loop operations. All things equal does raising FP on a 19 lb injector 5lb turn it into a 24. How about the reverse? Any thought would be appreciated. I'm curious why ford picked the static FP that they did? __________________ 88LX notch, Speedpro EFI 358windsor 11.2 to 1 compression, 5 lug baer claws all around..g force t5 and 3.55 gears. rwhp soon to come. Oh yeah...92 octane NO detonation.

03-18-2002, 09:25 PM	#2
LOWKEY Registered Member Join Date: Jan 2000 Location: greenvile, NC Posts: 161	There is a formula for calculating injector size @ different fp's in the link below. http://www.pro-flow.com/mustmath.htm http://www.pro-flow.com/t-car.html __________________ 89' Notch Stroked Poked & BLOWN low 11's and it goes around corners too Parts for Sale!! http://www.lowkey.stangnet.com/catalog.html

03-18-2002, 10:15 PM	#3
ArtMan Registered Member Join Date: Dec 1998 Location: Scarsdale, NY Posts: 45	Good Questions I often wondered why the stock fuel pressure is 39 psi too. I'll bet it has something to do with the injector design rather than the fuel pump design. In any case, that's what Ford has decided all stock EECs will assume is present at the injectors. When you increase fuel pressure through the use of an adjustable fuel pressure regulator more fuel flow occurs. The computer doesn't detect this during Wide Open Throttle operation, because the O2 sensors are shut off. This extra fuel can produce extra horsepower if accompanied by extra air. But there's a limit. Increasing fuel pressure excessively degrades the spray pattern of the injector and poor fuel delivery can occur. So, I'm not sure if you can effectively turn 19# injectors into 24s. The relationship between pressure and flow is not linear. Generally, if you feel the need for 24# injectors you should just upgrade, because you will likely do other mods that require them. Fooling the computer just goes so far.

03-18-2002, 11:34 PM	#4
DirtKing Registered Member Join Date: Feb 1999 Location: brooklyn center,mn,USA Posts: 169	thanks for the input...I'm not running the eek 4, but I'm interested in the theory behind it and fuel injection in general...anyone else?? __________________ 88LX notch, Speedpro EFI 358windsor 11.2 to 1 compression, 5 lug baer claws all around..g force t5 and 3.55 gears. rwhp soon to come. Oh yeah...92 octane NO detonation.

03-18-2002, 11:52 PM	#5
DirtKing Registered Member Join Date: Feb 1999 Location: brooklyn center,mn,USA Posts: 169	by the way, excellent link lowkey....interesting to see that it takes an aweful lot of pressure to increase flow. __________________ 88LX notch, Speedpro EFI 358windsor 11.2 to 1 compression, 5 lug baer claws all around..g force t5 and 3.55 gears. rwhp soon to come. Oh yeah...92 octane NO detonation.

03-18-2002, 11:57 PM	#6
exgmguy Registered Member Join Date: Feb 1999 Location: Utica, Michigan Posts: 2,631	When I hit the spray my injectors see a tad under 100 psi. They will go static if ran at that pressure for more than a 1/4 mile at a time. __________________ 1988 Mustang GT stock bottom 302, C4 10.9 @ 128 with 8 psi of Novi 1000 boost!----STOLEN 1989 Mustang notchback Warmed up 306 with a Procharger.

03-19-2002, 02:17 PM	#7
RED92LX50 Registered Member Join Date: Aug 1999 Location: Fairfax, VA Posts: 220	I have seen mentioned on other posts that the computer (over time - not sure how long) will adjust to the modified fuel pressure, effectively resetting it??? Is this true? Basically, it was stated that you could adjust your FP at the dyno to get peak HP, but after a while the computer would adjust to offset your changes (effectively cancelling your FP adjustment). Any truth to any of this? __________________ 1992 LX 5.0 Convertible Red/Blk Gears, Exhaust, bolt-ons... R.H.C. #51

03-19-2002, 02:40 PM	#8
FdMust88 Registered Member Join Date: Apr 1999 Location: Massachusetts Posts: 84	Although the site: http://www.howstuffworks.com/fuel-injection.htm may not directly answer your question(s), I felt as though there is enough valuable information listed on the site worth sharing with others.. They have some pretty cool stuff all throughout the site; check it out... __________________ 91LX, Modifications include: MAC Cold Air Induction Kit, MAC Headers and Cat-Back Exhaust, BBK H-Pipe, Edelbrock 70mm T.B., Pro-M 75mm MAF, MSD Wires and coil, NGK plugs, Pro 5.0 shifter, Underdrive Pullies, Kirban Fuel Pressure Regulator, Koni Adj. Sport struts & shocks, FMS springs, Maximum Motorsports Caster/Camber Plates, Strut tower brace, Kirkey Seats, and some Autometer gauges. Probably a few things I've forgotten also.. 1991 Mustang LX

03-19-2002, 10:40 PM	#9
juiceman Registered Member Join Date: Jan 2001 Location: ny Posts: 197	raising fuel pressure will in turn raise injector flow rate and vise versa. ford likely picked that stock pressure based on those injectors flowing 19 lbs. hr. at said press. for info and some formulas that will help and explain more go to www.msdignition.com click on fuel management

03-20-2002, 04:01 PM	#10
ArtMan Registered Member Join Date: Dec 1998 Location: Scarsdale, NY Posts: 45	87-95 Red, I don't think so. The '87 to '95 Stangs did not adjust fuel pressure through the EEC. As noted above the EEC did re-adjust pulse width during closed loop operation, but that's not what we're talking about here. WOT only. Not sure about '96 and newer, though.

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