electric fuel pump?

britlude · Post by **britlude** » Sat May 03, 2008 11:15 pm

looks just like one of these..... aftermarket replacement by 'commercial ignition', nuneaton, england...

paulc · Post by **paulc** » Mon May 05, 2008 6:00 pm

yes - you are all right on thge oil pressure switch. It's a ground switch. it'd work perfect if it was a + switch, but...

How about this approach? It's the charging light from the alternator.

paulc · Post by **paulc** » Mon May 05, 2008 6:02 pm

from here: http://www.thesamba.com/vw/forum/viewto ... ump+wiring

paulc · Post by **paulc** » Mon May 05, 2008 6:20 pm

a few more ideas

paulc · Post by **paulc** » Tue May 27, 2008 5:15 pm

how about this? Does this make sense?

DannyP · Post by **DannyP** » Wed May 28, 2008 2:19 am

I really like this last one. You could run it off an oil switch, VW has them in both closed w/pressure and open w/pressure. I think the Megajolt user out one is good though, considering that is the name of this forum

paulc · Post by **paulc** » Wed May 28, 2008 4:08 pm

did i get the relay wiring right? I'm not a relay expert / regular user, so it's still a bit hazy for me.

DannyP · Post by **DannyP** » Thu May 29, 2008 2:16 am

Wiring looks perfect, it makes me think "WHy didn't I think of that?"

I've been using auto relays for stereo/alarm/starters for over 25 years. What's my excuse? Don't have one

Supercharged Nat · Post by **Supercharged Nat** » Thu May 29, 2008 5:51 pm

the onyl issue with the last diagram is- if the megjolt went down for what ever reason, would you be able to get home- limp home mode wouldnt be much use then?

paulc · Post by **paulc** » Mon Jun 02, 2008 7:16 pm

then i would have to mc gyver it to the battery. i can be pretty crafty with a paperclip and a piece of gum.

good stuff - thanks guys.

alexander · Post by **alexander** » Mon Jan 19, 2009 3:44 am

hi. just bumping this thread as i dont think i ever got around to mentioning it previously.

while the above idea are workable for shutting off an electric fuel pump when the engine stops, the best solution is simply to buy safety relay as used on LPG installations. they are very common in australia - perhaps less so in europe - but are designed to do this very job. they are basically a normal relay, but with a timer such that the relay shuts off if it does not receive a voltage pulse every few seconds. that pulse can come from the coil -ve or a spark plug lead. it avoids all the tricky issues with cranking revs being lower than MJ abilitiy to measure, or with having to build up oil pressure before the car will start.

i have one on my LPG fitted jeep, but am about to put an extra one in for the electric fuel pump

regards
alexander.

Gilesy998 · Post by **Gilesy998** » Mon Jan 19, 2009 1:11 pm

brentp wrote:Hi Paul,

To activate a fuel pump you would want an output that is enabled above a low RPM value. The MJLJ can only measure RPM down to 457 RPMs- higher than most engines crank over at. For this reason the user outputs aren't well suited for this purpose.

However, there may be a work around that would still benefit from using the outputs. Here's how it might work:

The fuel pump would be powered by either the enabled output *or* with the key to the 'start' position (cranking). Once the engine is running, the engine would be at idle or higher, enabling the user output and the fuel pump. If the engine stalls, the output will be disabled, and therefore disable the fuel pump.

My idea is exactly the same, but rather than using a live-while-cranking feed, would suggest a momentary push-button to feed the pump 12V, that way you can hold the button while you turn the engine over, and even prime the injection system prior to cranking.

Hididng the switch makes a handy immobiliser too.

paulc · Post by **paulc** » Thu May 14, 2009 3:04 am

Gilesy998 - see the last diagram.

it works perfectly - i can attest to that.

NITROPIXIE · Post by **NITROPIXIE** » Thu May 14, 2009 2:57 pm

Paulc,

I quite like the idea of your last diagram but just to get my head around it, is the following description correct.

The circuit operates by having a constant 12v to the relay coil (or as i would, Ignition position 2 so is switched off when ignition is off, don't like things on constantly as there is a chance of a flat battery). The relay is operated by megajolt supplying a ground once the car has started ie above 500 rpm as set in the software.

When starting the engine, the 12v supplied to crank over the engine is at the same time supplied to the fuel pump and therefore supplying fuel to the engine during cranking. Once the engine has started and rises above 500rpm then the relay is energised and 12v to the pump is then supplied via a seperate supply.

As a safety feature i probably would add to this by placing a a knock?? switch in case of a crash or bump between the realy and the fuel pump itself.

On another note what alexander is talking about i believe are quite common in VW Golfs and the like over here. I forget what they are called but definately food for thought.

Brent are you putting fuel pump control on your next project????

Post by **brentp** » Thu May 14, 2009 3:07 pm

Not specifically in MJ2, but I imagine one of the user outputs can be purposed for this, as control over the user outputs will be much more flexible.

Autosport Labs

electric fuel pump?

electric fuel pump safety shutoff