Fuel pressure mod
Thread Starter
Burning Brakes
Joined: Feb 2007
Posts: 786
Likes: 6
From: Manassas VA/Flagler Beach FL
St. Jude Donor '13,'19
Fuel pressure mod
I read somewhere that if you remove the vacuum line from the fuel pressure regulator and plug it, you will get better mileage and better acceleration. Myth or fact?
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
vacuum line
removing the vacuum line may work for you if you have a fuel delivery problem, by masking the problem by increasing the fuel pressure.
It doesn't hurt anything. If you had an adjustable fuel pressure regulator set at 45 normal, 47-50 with the vacuum line off, you would only more finely atomize the fuel droplets, and in essence, yes the mileage would increase.
As for performance, I think the injector optimum pressure is 47-49 PSI, and increasing past that point, would make the injector inefficient, and actually reduce volume.
Everything is a trade off. It just depends on what you reallly want. a 30 mpg corvette to get 32mpg? or a 30 mpg corvette to go faster quicker?
I have removed the vacuum line, and in 115 degree heat here in phoenix, it seems to run better, even if it is just a finer mist that equates to better internal fuel cooling.
It doesn't hurt anything. If you had an adjustable fuel pressure regulator set at 45 normal, 47-50 with the vacuum line off, you would only more finely atomize the fuel droplets, and in essence, yes the mileage would increase.
As for performance, I think the injector optimum pressure is 47-49 PSI, and increasing past that point, would make the injector inefficient, and actually reduce volume.
Everything is a trade off. It just depends on what you reallly want. a 30 mpg corvette to get 32mpg? or a 30 mpg corvette to go faster quicker?
I have removed the vacuum line, and in 115 degree heat here in phoenix, it seems to run better, even if it is just a finer mist that equates to better internal fuel cooling.
Thread Starter
Burning Brakes
Joined: Feb 2007
Posts: 786
Likes: 6
From: Manassas VA/Flagler Beach FL
St. Jude Donor '13,'19
fuel pressure mod
Thanks for the feedback.
Jeff at CAM in NC analyzed my scan data (high lean block number, no codes) and said that usually means a suspect fuel pump. Would this mod make it work easier? I'm trying to squeeze all the life I can out of since it's a hassle to replace.
Jeff at CAM in NC analyzed my scan data (high lean block number, no codes) and said that usually means a suspect fuel pump. Would this mod make it work easier? I'm trying to squeeze all the life I can out of since it's a hassle to replace.
Safety Car
Joined: Jul 2004
Posts: 3,845
Likes: 30
...my pump at times would register a good pressure and at others would not until one day it left me in te driveway. replace the pump (about an hours work) and be done with it....
Melting Slicks
Joined: Jan 2002
Posts: 2,238
Likes: 4
From: Milan
The best mileage it's false. You will use more gas or the same gas as before if the computer (ECM) can compensate the added fuel reducing the BLM up to 108 . If you see 108 on the datalog you are using more gas than before even if the ECM on the dash istant MPG is saying less.
If BLM are above 108 you are using the same gas.
With the added fuel pressure the inj pulse widht will be less longer than before and the computer will say you are using less gas. (..but it's not true..)
-Beppe-
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Race Director
Joined: Jun 2004
Posts: 13,960
Likes: 707
From: WI
If you suspect fuel pump .... the last think i would do is to raise the fuel pressure removing the vacuum input.
The best mileage it's false. You will use more gas or the same gas as before if the computer (ECM) can compensate the added fuel reducing the BLM up to 108 . If you see 108 on the datalog you are using more gas than before even if the ECM on the dash istant MPG is saying less.
If BLM are above 108 you are using the same gas.
With the added fuel pressure the inj pulse widht will be less longer than before and the computer will say you are using less gas. (..but it's not true..)
-Beppe-
The best mileage it's false. You will use more gas or the same gas as before if the computer (ECM) can compensate the added fuel reducing the BLM up to 108 . If you see 108 on the datalog you are using more gas than before even if the ECM on the dash istant MPG is saying less.
If BLM are above 108 you are using the same gas.
With the added fuel pressure the inj pulse widht will be less longer than before and the computer will say you are using less gas. (..but it's not true..)
-Beppe-
Also from what I know, better atomization is good but not at the expense of being pig rich. This is why you size the injector correctly. Right size injector, right atomization, right fuel pressure. When you unplug the regulator it can no long change the fuel pressure at part throttle. This is what the full throttle fuel pressure is so you are running WOT pressure all the time. If you set your WOT fuel pressure super high you can gain atomization but get to rich.
Thread Starter
Burning Brakes
Joined: Feb 2007
Posts: 786
Likes: 6
From: Manassas VA/Flagler Beach FL
St. Jude Donor '13,'19
Also from what I know, better atomization is good but not at the expense of being pig rich. This is why you size the injector correctly. Right size injector, right atomization, right fuel pressure. When you unplug the regulator it can no long change the fuel pressure at part throttle. This is what the full throttle fuel pressure is so you are running WOT pressure all the time. If you set your WOT fuel pressure super high you can gain atomization but get to rich.
So far, four nays and three yeas. Could it be a debate? The modders versus the stockers...
Race Director
Joined: Jun 2004
Posts: 13,960
Likes: 707
From: WI
It's easy and cheap to check the FP. Tape a gauge to the window and do a few WOT runs, try to get high RPM. If the FP falls off at all from where it is set, there is a problem. Have you checked the vacuum line at the regulator for gas? It could be a problem with the regulator to. If the pump is going bad it could totally quit, leaving you stranded.
Being super rich can damage the cats. It could be from a leaking injector, there are a number of things it could be. Get a FP gauge. Also see if the FP leaks down with the gauge.
Being super rich can damage the cats. It could be from a leaking injector, there are a number of things it could be. Get a FP gauge. Also see if the FP leaks down with the gauge.
Drifting
Joined: Jan 2005
Posts: 1,354
Likes: 325
From: San Antonio Tx
The regulator is used to increase fuel pressure when the manifold vacuum decreases as when you push down on the gas pedal. You have no vacuum to the regulator at wide open throttle so it will not change anything at that point. It will only increase pressure at idle and low throttle. It might make it idle and cruise better if you are running lean now, but will not make more power when you put the pedal to the floor.
