Fuel Pressure

01-01-2001, 01:25 PM

Hi everyone, Happy New Year. Well I have a problem with my mustang. When I go to start it, it cranks over like the fuel pump isn't initializing the pressure.

The problem is that when I looked at my guage under the hood when my buddy turned the key on it went to 40psi immediately, but as soon as the pump went off it went back down to zero immediately.

I know the system is leaking somewhere, and I suspect a bad fpr because it is an old crane unit. Any help would be greatly appreciated, as I do not want to burn up my brand new 190lph fuel pump.

------------------
88GT stock shortblock, ported GT-40 iron heads, ported Edlebrock Performer intake, 24# inj, Pro-M 75mm Bullet MAM, 3.73, hurst short throw, F-303, electric fan, alum rad, FMS HD clutch, R134a ac conversion, 70mm TB , and some other stuff I probably forgot, best run so far on ET streets is 13.02@106 with a 1.87 60ft.

01-02-2001, 10:14 AM

Anybody please help, any and all suggestions welcome.

Mach 1 · 01-02-2001, 12:38 PM

do a visual inspection for the leak. If you cant find anything, change the regulater. It could be bleeding into return.

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1993 GT/AOD
'93 Mustang GT

jimberg · 01-02-2001, 05:15 PM

I take it that the FPR used to hold pressure? Did you check the FPR after you installed the fuel pump? Some fuel pumps will allow the fuel to spill back into the tank allowing the pressure to drop.

If you try to start the engine immediately after you turn the key (before the fuel pump stops) does it start any better? Does it start at all? I probably should have asked that first, but I get the impression that it does since you are concerned about burning out the fuel pump.

Do you have a hand vacuum pump that you can use to apply vacuum to the FPR? If you do, hook it to the FPR and apply vacuum while the fuel pump is running to see if the fuel pressure drops as you add vacuum. Fuel pressure should hold steady as you hold the vacuum pressure steady. E.g. If you apply 5 psi of vacuum, the fuel pressure should drop 5 psi and hold constant as long as 5 psi is being applied. If the pressure doesn't drop, replace the FPR. That means you probably have a bad diaphragm.

If you don't have a hand vacuum pump, what happens to the pressure as you crank it over? Does it drop or stay constant?

Just some ideas.

------------------
351W 89 Mustang GT Convertible

01-02-2001, 09:50 PM

I did the mods all at once and the fpr is probably 6 yrs old. I didn't have money for a fpr at the time so my friend gave it to me.

When I first started my car the fpr leaked a little. I didn't notice it until the car was already running for a while. I saw gas puddled on the intake. I started it again and it wasn't leaking. I kept checking it periodically.

I do hear a hissing sound by the fpr when the engine is running. My car also runs lean and only gets cured when I crank the fuel pressure up to 50psi at idle. I didn't drive the car much because I knew something was wrong.

Thanks guys, I will try what you have suggested.

exgmguy · 01-02-2001, 10:08 PM

If the pressure drops instantly to zero you have a leak somewhere.

A) all over the intake
B) In the cylinders. (leaking injectors)
c) regulator into the return line.

After it bleeds down check the plugs to see if any of them are wet with gas. If not, and there are no visual leaks, the regulator is most likely bad.

jimberg · 01-03-2001, 01:20 AM

50 PSI at idle? I'm assuming you have the vacuum line connected when you check. I'd replace that sucker. I just installed a BBK adjustable and had problems with it leaking from the fuel pressure gauge port. That's something to check, too. Is your gauge leaking?

------------------
351W 89 Mustang GT Convertible

01-03-2001, 09:48 AM

The 50 psi at idle is with the vacuum hose off. It is definitely too much pressure, and I couldn't afford a new regulator at the time (college books and bills $2500 a semester plus $200-$400 in books per semester). I know it was running lean, by looking at the plugs. I turned up the fuel pressure until the plugs were a tan color.

My fpr is the steel crane unit, which doesn't have a guauge port. Any suggestions on the best fpr to buy? Thanks again for all your help, anymore ideas or suggestions are welcome.

[This message has been edited by 88GT5.013.02 (edited 01-03-2001).]

01-01-2001, 01:25 PM	#1
88GT5.013.02 Guest Posts: n/a	Fuel Pressure Hi everyone, Happy New Year. Well I have a problem with my mustang. When I go to start it, it cranks over like the fuel pump isn't initializing the pressure. The problem is that when I looked at my guage under the hood when my buddy turned the key on it went to 40psi immediately, but as soon as the pump went off it went back down to zero immediately. I know the system is leaking somewhere, and I suspect a bad fpr because it is an old crane unit. Any help would be greatly appreciated, as I do not want to burn up my brand new 190lph fuel pump. ------------------ 88GT stock shortblock, ported GT-40 iron heads, ported Edlebrock Performer intake, 24# inj, Pro-M 75mm Bullet MAM, 3.73, hurst short throw, F-303, electric fan, alum rad, FMS HD clutch, R134a ac conversion, 70mm TB , and some other stuff I probably forgot, best run so far on ET streets is 13.02@106 with a 1.87 60ft.

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01-02-2001, 10:14 AM	#2
88GT5.013.02 Guest Posts: n/a	Anybody please help, any and all suggestions welcome.

01-02-2001, 12:38 PM	#3
Mach 1 Registered Member Join Date: May 1999 Location: Georgia Posts: 3,866	do a visual inspection for the leak. If you cant find anything, change the regulater. It could be bleeding into return. ------------------ 1993 GT/AOD '93 Mustang GT

01-02-2001, 05:15 PM	#4
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	I take it that the FPR used to hold pressure? Did you check the FPR after you installed the fuel pump? Some fuel pumps will allow the fuel to spill back into the tank allowing the pressure to drop. If you try to start the engine immediately after you turn the key (before the fuel pump stops) does it start any better? Does it start at all? I probably should have asked that first, but I get the impression that it does since you are concerned about burning out the fuel pump. Do you have a hand vacuum pump that you can use to apply vacuum to the FPR? If you do, hook it to the FPR and apply vacuum while the fuel pump is running to see if the fuel pressure drops as you add vacuum. Fuel pressure should hold steady as you hold the vacuum pressure steady. E.g. If you apply 5 psi of vacuum, the fuel pressure should drop 5 psi and hold constant as long as 5 psi is being applied. If the pressure doesn't drop, replace the FPR. That means you probably have a bad diaphragm. If you don't have a hand vacuum pump, what happens to the pressure as you crank it over? Does it drop or stay constant? Just some ideas. ------------------ 351W 89 Mustang GT Convertible

01-02-2001, 09:50 PM	#5
88GT5.013.02 Guest Posts: n/a	I did the mods all at once and the fpr is probably 6 yrs old. I didn't have money for a fpr at the time so my friend gave it to me. When I first started my car the fpr leaked a little. I didn't notice it until the car was already running for a while. I saw gas puddled on the intake. I started it again and it wasn't leaking. I kept checking it periodically. I do hear a hissing sound by the fpr when the engine is running. My car also runs lean and only gets cured when I crank the fuel pressure up to 50psi at idle. I didn't drive the car much because I knew something was wrong. Thanks guys, I will try what you have suggested.

01-02-2001, 10:08 PM	#6
exgmguy Registered Member Join Date: Feb 1999 Location: Utica, Michigan Posts: 2,631	If the pressure drops instantly to zero you have a leak somewhere. A) all over the intake B) In the cylinders. (leaking injectors) c) regulator into the return line. After it bleeds down check the plugs to see if any of them are wet with gas. If not, and there are no visual leaks, the regulator is most likely bad.

01-03-2001, 01:20 AM	#7
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	50 PSI at idle? I'm assuming you have the vacuum line connected when you check. I'd replace that sucker. I just installed a BBK adjustable and had problems with it leaking from the fuel pressure gauge port. That's something to check, too. Is your gauge leaking? ------------------ 351W 89 Mustang GT Convertible

01-03-2001, 09:48 AM	#8
88GT5.013.02 Guest Posts: n/a	The 50 psi at idle is with the vacuum hose off. It is definitely too much pressure, and I couldn't afford a new regulator at the time (college books and bills $2500 a semester plus $200-$400 in books per semester). I know it was running lean, by looking at the plugs. I turned up the fuel pressure until the plugs were a tan color. My fpr is the steel crane unit, which doesn't have a guauge port. Any suggestions on the best fpr to buy? Thanks again for all your help, anymore ideas or suggestions are welcome. [This message has been edited by 88GT5.013.02 (edited 01-03-2001).]