Fuel Pressure Sender Unit?

1bad67sbf · Jul 18, 2013

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 · Jul 19, 2013

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 · Jul 19, 2013

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

TrophyHead is right

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

1bad67sbf · Jul 19, 2013

lol, you don't want to know. :nonono:

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 · Jul 19, 2013

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?

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

1bad67sbf · Jul 19, 2013

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.

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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