How to activate a fuel pump with vacuum/boost?

[maca]

Hey Guys
I am running the Aeromotive duel pumps on E85. My car is also a weekend cruiser so I think running 2 pumps all the time may or may not be ok?
Aeromotive recommend running one pump all the time and having the other come on when vacuum drops.
Can anyone tell me how to achieve this?

[ZEOHSIX]

Use a Hobbs pressure or vacuum switch to activate a fuel pump relay.

[Kevin Johnson]

You might want to consider some type of an electronic "dashpot" setup to avoid lag problems during rapid throttle position changes (too rapid rate of switching on and off of the pump). Lots of EE's on the forum.

[maca]

So you're saying the pump may lag a little during the critical time and i could switch it on manually instead?
What's EEs?

[The Radius Kid]

Run both all the time and get a better regulator/return system.

[Kevin Johnson]

Electrical Engineers

[peejay]

If you're fuel injected, almost any aftermarket fuel system capable of flex fuel operation can also handle staged fuel pumps, generally switching the second one on when injector duty cycle gets to a certain threshold.

If you can't do that, you could try a vacuum switch, but it's probably easier to just run both full time and two pressure regulators if one proves to be insufficient. I had to do that once with a big single pump, it wasn't pretty but without doing that I was getting 90psi fuel pressure at idle.

[user-612937456]

Accelerator switch? Wot switched on gives fuel pump time to fully charge before it's volume is needed. And of course use it to trigger a relay.

[user-23911]

Run both all the time and get a better regulator/return system.

That's a really bad idea.

For a start you're running the 2nd pump when it's not needed.
That adds 10 to 15 A to the electrical load at idle.
That drops the idle voltage (which in turn causes other problems)
You're flowing all that extra fuel from the tank to the engine and back for no reason.
That heats the fuel (that's the lost electrical power)
Then you need the extra regulator capacity and line capacity in order for it to return to the tank.....for no reason.
You'll find that with just one pump flowing at full voltage , you'll need 2 regulators to keep the idle pressure down to the proper spec, unless it's a really big reg.


This is the no 1 mistake that the majority of ricers make when upgrading their japper turbos.


There's several ways of doing it, it comes down to what you've already got fitted.

Normally the first pump (255l/h or bigger) is also run in 2 stages with a switchable resistor in the supply circuit.
That's because even with just 1 big pump, there's too much fuel to be regulated at full voltage for low load.

The key to doing it properly is to have sufficient fuel for max RPM / max load and at the same time to NOT have excessive pressure at idle. That way it should idle like it came out of the factory and still make good power.


Need to flow test the whole thing too..........you'll learn lots.
Like how everyone else just makes it all up as they go.

[Seanh832]

Why not Use Aeromotive's fuel pump controller instead? Its programmable and they said you can set it from zero to full speed.
https://www.summitracing.com/parts/aei-16306/overview/

[A_VAS]

I use a Hobbs type switch, made by Honeywell. it is normally open, and closes when it sees ~4 to 5psi of pressure.
you run a T off a boost referenced line, and run a hose to the switch, with simple 2 wires. Switch closes and can be used to trigger a relay sending power to the 2nd pump.
I believe this is a pretty common way to do it...and it's independent of the tuning software

[Racerrick]

Why not Use Aeromotive's fuel pump controller instead? Its programmable and they said you can set it from zero to full speed.
https://www.summitracing.com/parts/aei-16306/overview/

That's what I use even with a dual fuel nitrous blower set up. They work well and the pumps last longer.

[DaveMcLain]

There are some really slick vacuum operated switches that are used on Harley Davidson Sportster motorcycles which are used to turn an vacuum advance on or off at a set manifold vacuum. I guess that works better in the pulsing environment of a two cylinder engine. Anyway, you could use one of those through an accessory relay to turn one of the pumps off and on at the manifold vacuum of your choice and it would work slick, simple and inexpensively. You can adjust them too to fine tune the system.

[maca]

Thanks guys
The cheaper way is best for me as I now have several cars.
I only run 8 to 12 psi of boost so I would like to find a switch that comes on with low vacuum rather than boost as if it comes on with boost is may be a little late.
Maybe when vacuum drops below 5 or even zero.
The only vacuum switch I have used before is for a vacuum pump for my brakes like this one
http://i.ebayimg.com/00/s/Mzc1WDUwMA==/$(KGrHqR,!ooFBul4Z8S7BQscglR0Lw~~60_35.JPG
So I will google some to try and find one.

[Rick Finsta]

Pump controller or Fuelab makes a really trick regulator/pump combo that uses PWM for pump speed based on pressure at the rail/bowl and can be vacuum referenced.

ETA: A vacuum switch won't have hysteresis, right? Could be problematic.