Purpose of the Fuel Pressure Regulator Vacum Hose?
10-18-2003, 08:55 PM
#1
Registered User
Thread Starter
Join Date: Sep 2003
Posts: 125
Purpose of the Fuel Pressure Regulator Vacum Hose?
I'm wondering if it need's to stay hooked up or not? I notice that as I get on the gas the fuel pressure increases when the hose is connected. If I leave it unhooked it just runs at a constant pressure all the time. Which is a better way to have it, and why? thanks
10-18-2003, 09:43 PM
#2
Registered User
Join Date: Dec 1969
Location: Little Rock, AR
Posts: 27,714
The purpose of the vacuum line is to allow the regulator to do what it is put there for-change the pressure. You don't need high pressure when the demand for fuel is low (like idle). High load situations make the vacuum go down. When this happens the regulator increases the pressure.
10-18-2003, 10:20 PM
#3
Registered User
Thread Starter
Join Date: Sep 2003
Posts: 125
Originally posted by shoebox
The purpose of the vacuum line is to allow the regulator to do what it is put there for-change the pressure. You don't need high pressure when the demand for fuel is low (like idle). High load situations make the vacuum go down. When this happens the regulator increases the pressure.
The purpose of the vacuum line is to allow the regulator to do what it is put there for-change the pressure. You don't need high pressure when the demand for fuel is low (like idle). High load situations make the vacuum go down. When this happens the regulator increases the pressure.
10-19-2003, 10:03 PM
#5
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,824
The vacuum "compensation" line is there to maintain a constant DIFFERENTIAL fuel pressure accross the injector. The injectors are rated at 43.5psi DIFFERENTIAL pressure.... the difference between the inlet to the injector - the fuel rail - and the outlet of the injector - the intake manifold.
At idle, there is a vacuum in the intake manifold, so in order to keep the DIFFERENTIAL pressure the same, the fuel rail pressure must be reduced in proportion to manifold vacuum. 36psi rail pressure minus the intake vacuum (remember... intake vacuum is a "minus" pressure, and minus a minus = a plus) will equal 43.5psi..... +36psi - (-7.5psi) = 43.5psi.
When you open the throttle, intake manifold vacuum decreases, so the fuel rail pressure must be increased to keep the DIFFERENTIAL pressure the same. At WOT, there is virtually no vacuum in the intake manifold, and the rail pressure must rise to 43.5psi..... 43.5 - 0 = 43.5.
So..... yes, you need to keep the vacuum compensation line connected, because the injectors are rated at 43.5psi DIFFERENTIAL pressure and the PCM is programmed with the flow rate for that pressure.
At idle, there is a vacuum in the intake manifold, so in order to keep the DIFFERENTIAL pressure the same, the fuel rail pressure must be reduced in proportion to manifold vacuum. 36psi rail pressure minus the intake vacuum (remember... intake vacuum is a "minus" pressure, and minus a minus = a plus) will equal 43.5psi..... +36psi - (-7.5psi) = 43.5psi.
When you open the throttle, intake manifold vacuum decreases, so the fuel rail pressure must be increased to keep the DIFFERENTIAL pressure the same. At WOT, there is virtually no vacuum in the intake manifold, and the rail pressure must rise to 43.5psi..... 43.5 - 0 = 43.5.
So..... yes, you need to keep the vacuum compensation line connected, because the injectors are rated at 43.5psi DIFFERENTIAL pressure and the PCM is programmed with the flow rate for that pressure.
Thread
Thread Starter
Forum
Replies
Last Post
chevroletfreak
LT1 Based Engine Tech
202
07-04-2005 05:00 PM
F(ast)-body
LT1 Based Engine Tech
8
02-26-2003 09:05 AM