Correct way to adjust fuel pressure?

1982matthew · April 23rd, 2008, 05:48 PM

I have an under hood gage and I was wondering the correct procedure to adjust fuel pressure because when I do it the car starts surging and shuts down.

nolife · April 23rd, 2008, 07:32 PM

You do have an adjustable FPR right? The stock one is not adjustable

Remove the vacuum line and temporarily plug or crimp it and adjust the FPR for 39#.

Surging related to fuel pressure can be caused by too much fuel pressure or in some cases, larger then stock injectors can surge at the stock setting at 39#, if that is the case, try something a few pounds lower and see if that helps. You may also have other surge related problems and the fuel pressure is making it worse.

ryans88gt · April 23rd, 2008, 11:14 PM

^+1 solid info.

1982matthew · April 24th, 2008, 04:36 PM

I have a 306 with trickflow heads, cam,intakes,full exhaust etc...and I have it set at like 25 to 30ish and I thought that seemed alittle low but it surges when I raise it.

nolife · April 24th, 2008, 04:47 PM

That seems to low. Assuming your gauge is right, I'd take your pressure back up and start the process to eliminate why its surging. There are plenty of old threads on MM and many other places online that go into extreme detail on tracking down fox body idle surging.

1982matthew · April 24th, 2008, 04:54 PM

yeah I was looking at some yesterday,it just seems weird to me that it gets that much worse with just a little pressure increase.

ryans88gt · April 24th, 2008, 08:24 PM

It can happen. My 89 runs like crap with more than 35 PSI and 30 lb injectors.

1982matthew · April 24th, 2008, 08:36 PM

thats about the pressure mine gets to before it gets pissed off at me.....

notch9350 · April 24th, 2008, 08:36 PM

I thought 43 was more accurate with an adjustable, I think aeromotive even recommends an initial setting of 48. This is a mod I've been researching a little and those pressures just seemed a little low?

90 lx notch · April 25th, 2008, 12:23 AM

stock is 39 mine is at 35 and the engine runs good

ryans88gt · April 25th, 2008, 12:43 AM

I like to run mine at 30 PSI vacuum on since it hits about 100 PSI during boost.

nolife · April 25th, 2008, 10:15 AM

My base is at about 35 (80 with the FMU) and I get surging every once in a while. A 2 or 3 second rev above 2k usually makes it settle back down. I feel like an idiot sitting in traffic revving it though. Its like I'm calling out to everyone near by that I want to race or something. "No I'm not trying to be cool, I'm just trying to keep my car from stalling. Move along, nothing to see here" At least some other fox body owners will yell out, dude, idle surging?
I'm finally getting some dyno and A/F time on Saturday so I'll see if that is a good setting for me. I'm only pushing 10# boost and my 6k rev limiter pill in so hopefully I don't blow a head gasket

I have a feeling I'm not going to be satisfied with the results.

ryans88gt · April 25th, 2008, 11:08 AM

Take out the 6K pill and rely on the stock rev limiter. It is actually softer than the MSD.

I'll bet you are better than 400 at the wheels.

Try dropping your base fuel pressure, it really settled my car. Also, play around with different clocking rotations of the MAF.

1982matthew · April 25th, 2008, 02:35 PM

Ryan, can you explain different clocking of the maf for me, thanks

April 23rd, 2008, 05:48 PM	#1
1982matthew Regular 1993 GT 13.2@105 Join Date: Mar 2008 Location: Nazareth, Pa Posts: 173	Correct way to adjust fuel pressure? I have an under hood gage and I was wondering the correct procedure to adjust fuel pressure because when I do it the car starts surging and shuts down.

April 23rd, 2008, 07:32 PM	#2
nolife Hardcore Enthusiast Join Date: Dec 2006 Posts: 1,226	You do have an adjustable FPR right? The stock one is not adjustable Remove the vacuum line and temporarily plug or crimp it and adjust the FPR for 39#. Surging related to fuel pressure can be caused by too much fuel pressure or in some cases, larger then stock injectors can surge at the stock setting at 39#, if that is the case, try something a few pounds lower and see if that helps. You may also have other surge related problems and the fuel pressure is making it worse. __________________ 1991 GT - Original owner, all stock 1988 GT - The project car

April 23rd, 2008, 11:14 PM	#3
ryans88gt MM Fanatic Join Date: May 2007 Location: Bloomington, IL Posts: 3,761	^+1 solid info. __________________ 89 LX 515 hp 497 ftlbs 11.3 @ 125 mph 88 GT 11.4 @ 118

April 24th, 2008, 04:47 PM	#5
nolife Hardcore Enthusiast Join Date: Dec 2006 Posts: 1,226	That seems to low. Assuming your gauge is right, I'd take your pressure back up and start the process to eliminate why its surging. There are plenty of old threads on MM and many other places online that go into extreme detail on tracking down fox body idle surging. __________________ 1991 GT - Original owner, all stock 1988 GT - The project car

April 24th, 2008, 08:24 PM	#7
ryans88gt MM Fanatic Join Date: May 2007 Location: Bloomington, IL Posts: 3,761	It can happen. My 89 runs like crap with more than 35 PSI and 30 lb injectors. __________________ 89 LX 515 hp 497 ftlbs 11.3 @ 125 mph 88 GT 11.4 @ 118

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April 24th, 2008, 04:36 PM	#4
1982matthew Regular 1993 GT 13.2@105 Join Date: Mar 2008 Location: Nazareth, Pa Posts: 173	I have a 306 with trickflow heads, cam,intakes,full exhaust etc...and I have it set at like 25 to 30ish and I thought that seemed alittle low but it surges when I raise it.

April 24th, 2008, 04:54 PM	#6
1982matthew Regular 1993 GT 13.2@105 Join Date: Mar 2008 Location: Nazareth, Pa Posts: 173	yeah I was looking at some yesterday,it just seems weird to me that it gets that much worse with just a little pressure increase.

April 24th, 2008, 08:36 PM	#8
1982matthew Regular 1993 GT 13.2@105 Join Date: Mar 2008 Location: Nazareth, Pa Posts: 173	thats about the pressure mine gets to before it gets pissed off at me.....

April 24th, 2008, 08:36 PM	#9
notch9350 Newbie '93 Notchback 5.0 Join Date: Mar 2008 Location: New Hampshire Posts: 18	I thought 43 was more accurate with an adjustable, I think aeromotive even recommends an initial setting of 48. This is a mod I've been researching a little and those pressures just seemed a little low?

April 25th, 2008, 12:23 AM	#10
90 lx notch Newbie 1990 mustang lx notch no track time Join Date: Apr 2008 Location: baltimore md Posts: 44	stock is 39 mine is at 35 and the engine runs good __________________ 90 LX NOTCH elec. fan, fenderwell intake, adjustable fuel reg w/ gauge, 75mm pro-m meter, 75mm ford racing tb and egr spacer, bbk pulleys & headers & offroad x-pipe, slp catback, 5 lug conversion, bullitt rims, 3.73 gears, battery relocation

April 25th, 2008, 12:43 AM	#11
ryans88gt MM Fanatic Join Date: May 2007 Location: Bloomington, IL Posts: 3,761	I like to run mine at 30 PSI vacuum on since it hits about 100 PSI during boost. __________________ 89 LX 515 hp 497 ftlbs 11.3 @ 125 mph 88 GT 11.4 @ 118

April 25th, 2008, 10:15 AM	#12
nolife Hardcore Enthusiast Join Date: Dec 2006 Posts: 1,226	My base is at about 35 (80 with the FMU) and I get surging every once in a while. A 2 or 3 second rev above 2k usually makes it settle back down. I feel like an idiot sitting in traffic revving it though. Its like I'm calling out to everyone near by that I want to race or something. "No I'm not trying to be cool, I'm just trying to keep my car from stalling. Move along, nothing to see here" At least some other fox body owners will yell out, dude, idle surging? I'm finally getting some dyno and A/F time on Saturday so I'll see if that is a good setting for me. I'm only pushing 10# boost and my 6k rev limiter pill in so hopefully I don't blow a head gasket I have a feeling I'm not going to be satisfied with the results. __________________ 1991 GT - Original owner, all stock 1988 GT - The project car

April 25th, 2008, 11:08 AM	#13
ryans88gt MM Fanatic Join Date: May 2007 Location: Bloomington, IL Posts: 3,761	Take out the 6K pill and rely on the stock rev limiter. It is actually softer than the MSD. I'll bet you are better than 400 at the wheels. Try dropping your base fuel pressure, it really settled my car. Also, play around with different clocking rotations of the MAF. __________________ 89 LX 515 hp 497 ftlbs 11.3 @ 125 mph 88 GT 11.4 @ 118

April 25th, 2008, 02:35 PM	#14
1982matthew Regular 1993 GT 13.2@105 Join Date: Mar 2008 Location: Nazareth, Pa Posts: 173	Ryan, can you explain different clocking of the maf for me, thanks

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