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  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech

Fuel Pressure Sender Unit?

  • Thread starter Thread starter 1bad67sbf
  • Start date Start date Jul 18, 2013

1bad67sbf

Active Member
Nov 24, 2010
674
1
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N. VA
Jul 18, 2013
#1
  • Jul 18, 2013
  • #1
I want to wire up a relay to kill my fuel pump once a set psi is reached. is the oem system just on a timer or does it pick up fuel psi then shut down?

thanks
 

TrophyHead

15 Year Member
Mar 18, 2003
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Jul 19, 2013
#2
  • Jul 19, 2013
  • #2
The oem one runs on a vacuum. And it's a return style fuel system meaning what isn't used goes back to tank.
 

jrichker

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Jul 19, 2013
#3
  • Jul 19, 2013
  • #3
1bad67sbf said:
I want to wire up a relay to kill my fuel pump once a set psi is reached. is the oem system just on a timer or does it pick up fuel psi then shut down?

thanks
Click to expand...
TrophyHead is right


The next question is why? What are you trying to do?
 

1bad67sbf

Active Member
Nov 24, 2010
674
1
29
N. VA
Jul 19, 2013
#4
  • Jul 19, 2013
  • #4
lol, you don't want to know.
I just need to know what I can wire the relay trigger post to that will understand the system is at a set psi.
does the vacuum post on the fuel rail feed a signal to a controller that switches the relay or does the vacuum post control pressure?
 

jrichker

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In Remembrance. Thank you for your contributions
Mar 10, 2000
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Jul 19, 2013
#5
  • Jul 19, 2013
  • #5
1bad67sbf said:
lol, you don't want to know.
I just need to know what I can wire the relay trigger post to that will understand the system is at a set psi.
does the vacuum post on the fuel rail feed a signal to a controller that switches the relay or does the vacuum post control pressure?
Click to expand...
I really don't want to know what you are going to do? In that case you're going to get a really wild guess at what you can use to do what you want to do... Not my best effort to get you the best answer.
If it's that top secret, send me a non disclosure form and I'll consider signing it.

There is no electronic measurement of the fuel pressure built into the car. The engine vacuum moves a diaphragm connected to a needle valve that opens the valve to return more fuel to the tank at high vacuum (idle). As the vacuum drops off with an increase in throttle opening, the needle valve closes, returning less fuel to the tank.

The closest thing that you can buy at an auto parts place or salvage at the junkyard is the low pressure cutout switch for the A/C. It is set to close the contacts, turning the circuit on at about 25 PSI. Each 1/4 turn of the adjustment screw changes the pressure approximately 1 PSI. Use compressed air and a regulated air pressure source to set the switch to the pressure trip point you want.

See http://www.autozone.com/autozone/parts/1992-Ford-Mustang/A-C-Switch/_/N-ix24uZ91t6l for the A/C low pressure cutout switch and the wiring connector that goes with it.

Wiring connector for the pressure cutout switch


A/C low pressure cutout switch


Diagrams courtesy of Tmoss & Stang&2birds




See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif


Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif
 

1bad67sbf

Active Member
Nov 24, 2010
674
1
29
N. VA
Jul 19, 2013
#6
  • Jul 19, 2013
  • #6
rite on man, thanks for the tech help


jrichker said:
I really don't want to know what you are going to do? In that case you're going to get a really wild guess at what you can use to do what you want to do... Not my best effort to get you the best answer.
If it's that top secret, send me a non disclosure form and I'll consider signing it.
Click to expand...

A couple years ago you told me not to do what im doing and I don't want to turn this into a DO NOT DO thread...
thanks again
 
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