electric fuel pump?

paulc · Post by **paulc** » Thu May 01, 2008 10:54 pm

I have searched, but couldn't find much relivant info on this subject.

I have installed a rotory electric fuel pump on my 2L engine running dual downdraft webers 44IDFs. I have the MAP sensor plumbed into each manifold.

Is there any way to trigger the fuel pump to turn on from MJ? I have not installed the EDIS yet or got the car running as i am just in the wiring harnbess phase. The car is pretty basic and the ignition switch does not have a "car is running" position. Only an "on (start)", "off", and "accessory".

Any help on this subject would be very much appreciated as i'm sratching my head on how to wire up the fuel pump. I don't want it pumping with the engine not running.

Thanks.

edit: could i use the user output? http://www.autosportlabs.org/viewtopic. ... light=user

these only trigger when engine is runnin right (over 500rpm)?

I can't be the first person with this problem.

Post by **brentp** » Fri May 02, 2008 6:30 am

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.

britlude · Post by **britlude** » Fri May 02, 2008 1:33 pm

some applications have a oil pressure single pole change over switch controlling the pump, wired so that : common to the pump, normally open to the ignition supply, and the normally closed to the starter circuit.

the pump is powered if the starter motor is turning, then once started and running the oil pressure flips the switch and the pump runs via the ignition supply. if the motor stalls (as it did in mine when i rolled it!!!) the fuel pump stops!!!

you should be able to sort something from the alternator/dash light line too

Salamander · Post by **Salamander** » Fri May 02, 2008 1:53 pm

hi!, try to connect the fuel pump to the oil switch, when you start the engine, the oil pressure start the pump, low oil press stop the pump.

Post by **brentp** » Fri May 02, 2008 3:08 pm

Frankly, I like the oil pump switch better.

paulc · Post by **paulc** » Fri May 02, 2008 5:40 pm

those are really good ideas guys - thanks.

I had planned to install a relay and have it triggered when the starter is engadged and then another feed to the same relay that comes from a user out.

The oil pressure switch seems like a more elegant solution and i love the built in safety concept (except there would still be 4 carbs of float bowls full of fuel to burn at zero oil pressure)

Thanks!

MartinM · Post by **MartinM** » Fri May 02, 2008 11:07 pm

I must be being dense here....

An oil pressure switch like Salamander's (providing there's not too much PTFE tape rendering it completely isolated from ground!), switches the ground connection of a lamp when you have no/low oil pressure. At high pressure it goes open circuit and the light goes out.

So if you connect the fuel pump to the oil switch (I presume you're switching the earth side of the pump?) then no/low oil pressure will keep the pump running ie it will start as soon as you turn the ignition on and keep it running whenever the engine stops - which is exactly what you don't want

...goes to bed, preparing to be put right before the morning - it's been a long week!

alexander · Post by **alexander** » Fri May 02, 2008 11:28 pm

i'm with martin on that one...
in any case, brent's suggested work around sounds just fine, the only possible problem being that you cant make the fuel pump without turning the starter. that could potentially be annoying when troubleshooting fuel problems, for instance.

i note that the lpg installation in my jeep (and no doubt every other one) has a feature which switches off the gas after 5 seconds or so, if a steady flow of low voltage coil pulses is not received (i think that is how it does it anyway). so an alternative here is to use the same sort of control box for the petrol fuel pump.

alexander

Post by **brentp** » Sat May 03, 2008 1:35 am

I thought the oil pressure was a really good indication of engine running, but didn't consider the switch's behavior. If it's a pressure switch that closes on low pressure it could be inverted through a relay- You'd probably want to switch the pump's current through a relay in any case. Perhaps you could find a pressure switch that closes with pressure?

The other thing to consider is if cranking will generate enough oil pressure to actuate the switch- It could lead to long cranking times in the morning. If that proved to be a problem, you would need a fuel pump override while cranking- and then you might as well as implement the user-defined output solution.

Dimbit · Post by **Dimbit** » Sat May 03, 2008 7:21 am

You can determine if the engine's stalled using the MAP sensor - It's unlikely to reach 1 atmosphere while running, so a user out could tell you that. You still have the cranking problem though. Maybe with a firmware update that turns the output on for 20 seconds when powered up?

britlude · Post by **britlude** » Sat May 03, 2008 6:48 pm

just for future reference, rover SD1 v8's have a single pole change-over oil pressure switch, 3 terminals internally switched, for the fuel pump control as standard.

i know this, as it's what is fitted on mine!!!

you could get much the same effect using a standard oil pressure switch triggering a single pole change over relay.

Salamander · Post by **Salamander** » Sat May 03, 2008 8:09 pm

the oil switch can connected to the relay invert the polaritation to start the fuel pump, sorry my english.

I have connected to the buzzer, it's better when you run in track day

alexander · Post by **alexander** » Sat May 03, 2008 10:28 pm

britlude wrote:just for future reference, rover SD1 v8's have a single pole change-over oil pressure switch, 3 terminals internally switched, for the fuel pump control as standard.

i know this, as it's what is fitted on mine!!!

you could get much the same effect using a standard oil pressure switch triggering a single pole change over relay.

hi britlude, what exactly does the rover installation do?

regards
alexander.

britlude · Post by **britlude** » Sat May 03, 2008 10:57 pm

the rover installation is exactly as i described above, and i'm sure it's not just a rover thing....

the rover has a oil pressure activated change over switch (3 terminals) controlling the pump, wired so that : common terminal goes to the pump, normally open contact to the ignition supply, and the normally closed to the starter circuit.

when the starter motor is turning the pump is powered as there is no oil pressure, then once started and running the oil pressure flips the switch and the pump runs via the ignition supply. if the motor stops for any reason the fuel pump stops!!!

as Brent pointed out, lots or motor winding can get sufficient oil pressure to flip the contacts, as can be seen by the pump 'running on' if the cranking is stopped (but ignition still on) until the pressure subsides! I just take that as a good sign that the bearings aren't shot !!!

this came in handy when i rolled my car, as the engine stopped, by virtue if the ignition wires being ripped off as the engine mounting rubbers broke, and the pump stopped, despite the ignition still being on!

i'm running carbs, if you have injection you'd be running a straight ingition switched supply, and some sort of impact/bump switch

MartinM · Post by **MartinM** » Sat May 03, 2008 11:14 pm

Looks like I should take a position on some of these then

...eBay (UK) item 230247785814

Looks cheap...at the moment, until all the MJLJ'ers start bidding!