Using MJLJ to trigger a Facet Fuel Pump

16vescort · Post by **16vescort** » Fri Nov 05, 2010 12:20 pm

Hi All,

Just after some clarfication on how this would work.

I want to have the fuel pump on my Mk1 Escort to be "turned on" by MJ when it senses the engine is turning over, rather than just having it running on an ignition live.

The reason for this being - I don't want the pump running after a potential accident and spilling fuel everywhere, so if the engine stops so does the pump.

From reading the installation guide I can use one of MJLJ's option outputs, but as i undersatnd it these work on a switched earth??

The problem I have is the pump runs a switched live idea, and I will be running it through a heavy duty relay so wondered what people suggest?

My plan is this:
FP earthed to body via mounting kit / Live run to relay output terminal.

Relay supplied with ignition 12V live

Then i'm stuck as to how to wire up the other 2 options as relays normally run on a switched live..... HELP

Funky Diver · Post by **Funky Diver** » Fri Nov 05, 2010 3:53 pm

It's quite straight forward to do form the guide.

The bottom scenario covers what you need.

DannyP · Post by **DannyP** » Sun Nov 07, 2010 12:53 pm

As Funky says, use the relay wired as above. Any Bosch-type 30 amp automotive relay will do. Coil current is usually 50 ma, so the MJLJ will be fine with that. A Facet pump draws what, MAYBE 5 amps, so any relay from 20 amps up is fine, use 16 gauge wire or heavier, I would use 14, I always go a step or two heavier when it comes to wiring.

Alternatively, you could use an oil pressure switch to to activate the pump relay, but I like to use the MJLJ for gadgety-type stuff too

16vescort · Post by **16vescort** » Tue Mar 08, 2011 10:57 am

Cool, but is there anything need to program the MJLJ unit to do to action the output??

Post by **brentp** » Tue Mar 08, 2011 4:28 pm

The only issue with triggering fuel pumps with the Megajolt is that it cannot measure engine speed below about 450 RPMs. This could cause problems with activating the fuel pump while cranking. There were other thread on this subject, try searching 'fuel pump' to see what came out of those discussions.

16vescort · Post by **16vescort** » Fri Mar 25, 2011 11:56 am

thats not a problem Brent as the engine should fire from the fuel in the flaot on the webers - hence us wanting it to use the crank pick up to trigger the fuel pump relay - is that possible?

Will also search other threads as suggested.

Thanks

Spockie-Tech · Post by **Spockie-Tech** » Fri Mar 25, 2011 1:49 pm

I would add a momentary-contact "Prime" buitton to the system somewhere, just incase the webers bowls run dry. Ive had webers boil (percolate) after a hard thrash on a hot day, You dont want to get stuck with dry bowls and no way to get fuel back into them.

Or, you can get a rpm/safety switchs from any LPG conversion place. They give a short (~2s) prime pulse, then turn off the gas (fuel pump in your case) until they detect engine ignition pulses again.