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Fuel Pump starts when? #945437 05/14/09 06:17 PM
Joined: Sep 2005
Posts: 26
D
dayoldpoi Offline OP
Getting the Wheeling Fever
Should a fuel pump in a 1988 Trooper run briefly when the ignition is in the ON position or does it only run in the START position?


1988 Isuzu Trooper II
150,000 miles
starting to have more replaced parts than original parts
2.6 L 4 cyl 4X4
Never say die!
Re: Fuel Pump starts when? [Re: dayoldpoi] #945438 05/14/09 07:59 PM
Joined: Aug 2000
Posts: 4,868
Jim_Paget Offline
Roll Me Over
It runs briefly in the on position in order to pressurize the system for the start.


Jim Paget
88 YJ with a few changes

www.rrr4x4.com
Re: Fuel Pump starts when? [Re: Jim_Paget] #945439 05/14/09 11:29 PM
Joined: Apr 2000
Posts: 7,268
mlclark Offline
Isuzu Moderator
*****
I *think* that is true for the v6 engines. For the 2.6's, I think it only will run when you turn it to start. The system holds pressure (unlike the TBI systems) and in the 2.6, it won't run unless there is oil pressure and engine off, key on, should not give a signal to the pump to run. When the key is turned to start, it feeds battery voltage to the pump (system is already pressurized) and once the alt fires off, it then switches over to alt power.

Besides, the 2.6 fuel system is controlled by the fuel regulator, not the pump. If the pump turns on, it does not "know" when to turn off, excess fuel is just bypassed through the regulator. I suspect the TBI system may use the ECU to run the pump for a few seconds with the key in the on position.

Of course, this all started with I *think*.

Michael

Re: Fuel Pump starts when? [Re: mlclark] #945440 05/15/09 12:09 AM
Joined: Jun 2008
Posts: 785
V
vr4 Offline
Rock Warrior
*****
Quote
I *think* that is true for the v6 engines. For the 2.6's, I think it only will run when you turn it to start. The system holds pressure (unlike the TBI systems) and in the 2.6, it won't run unless there is oil pressure and engine off, key on, should not give a signal to the pump to run. When the key is turned to start, it feeds battery voltage to the pump (system is already pressurized) and once the alt fires off, it then switches over to alt power.

Besides, the 2.6 fuel system is controlled by the fuel regulator, not the pump. If the pump turns on, it does not "know" when to turn off, excess fuel is just bypassed through the regulator. I suspect the TBI system may use the ECU to run the pump for a few seconds with the key in the on position.

Of course, this all started with I *think*.

Michael


most likely correct. american cars tend to run the pump for a second when the key is turned to on. the japanese typically dont run it until start position.


87 Montero V6 SWB auto. dual bouncies
89 Montero V6 SWB 5 speed. dual bouncies
97 3000gt VR4 upgraded turbos, 10:1, E85
91 Stealth TT twin 18Gs, cams/heads, E85
03 cobra lightly modded <img src="/forums/images/graemlins/lol.gif" alt="" />
91 MR2 turbo
Re: Fuel Pump starts when? [Re: vr4] #945441 05/15/09 03:57 AM
Joined: Mar 2008
Posts: 9
H
HondaGuy Offline
Need a Spot
On 4 cyl., pump initially runs in start position (ign. switch through fuse 23 through non-energized fuel pump relay). When alternator produces voltage at White wire with Green stripe, the "engine" relay is energized and passes current to fuse 12, through the diodes, and then energizes the fuel pump relay. Fuse 24 then provides voltage through energized relay to fuel pump. Keep in mind this means you have to have working alternator to have good fuel pump operation.

Re: Fuel Pump starts when? [Re: HondaGuy] #945442 05/21/09 05:05 PM
Joined: Jun 2008
Posts: 785
V
vr4 Offline
Rock Warrior
*****
Quote
On 4 cyl., pump initially runs in start position (ign. switch through fuse 23 through non-energized fuel pump relay). When alternator produces voltage at White wire with Green stripe, the "engine" relay is energized and passes current to fuse 12, through the diodes, and then energizes the fuel pump relay. Fuse 24 then provides voltage through energized relay to fuel pump. Keep in mind this means you have to have working alternator to have good fuel pump operation.



damn...where were you a few months ago <img src="/forums/images/graemlins/lol.gif" alt="" />


87 Montero V6 SWB auto. dual bouncies
89 Montero V6 SWB 5 speed. dual bouncies
97 3000gt VR4 upgraded turbos, 10:1, E85
91 Stealth TT twin 18Gs, cams/heads, E85
03 cobra lightly modded <img src="/forums/images/graemlins/lol.gif" alt="" />
91 MR2 turbo







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