HELP - how to wire up a fuel pump

[sillycar chick]

Peoples, I am a bit of a newb when it comes to wires and stuff (but I am trying and getting better )

I have drawn up how I think I should wire it up so that I can have an on/off switch hidden under the dash. I think its right because I have done a thermo this way before.

BUT, to do it this way, I have to tap off the fuse panel to a wire which has power when the key is "on". I dont really like doing this, and its how I upset the wires last time (I only just got that all fixed for now). So is there another way of doing it so I can have a switch but not tap off the fuse panel? Or can anyone draw up a better diagram and post it up?

And Witzl: sorry if its copyright, I used your homepage on how to wire a thermo fan to start me off

[wilbo666]

That should work...

But you might want to think about using a Circuit Opening Relay, or a RPM triggered relay so that in the event that you have a crash and the engine stops (and there is a fuel leak) the pump doesn't keep going and make the car (and you?) burn...

Cheers
Wilbo

[sillycar chick]

Hmmm that's a good point.... where can I get me one of them relays... Jaycar? And are they expensive?

[RobertoX]

at a guess this would probably be required to be legal (could someone confirm this?), are you using the factory computer? Just follow the factory wiring diagram for that engine's installation


edit, you can get the relays from pretty much any efi toyota, mine came from a corolla at u-pull

[Celica_73]

Why not tap off the wire to your radio that turns it on with the Ignition. They all end up at the same point.

As for the wiring diagram that should work.

If you wanted to get fancy you could modify the wiring and make it a latching relay with a momentary switch. Meaning once the car is turned off you would have to Push the button again to start it. (Self enguaging)

[sillycar chick]

Its in a TA22 celica... the mech pump shat itself and I bought a leccy to get me home. Then I decided it worked well so kept it in there, but I still have to wire it properly (hasnt been back on road since). So therefore there is no ECU.

[RobertoX]

ah sorry, I presumed EFI...
The thing with the circuit opening relays is that they rely on a signal from some thing that is only running when the engine is ticking over (as discussed in another thread this can be an ecu output or a switch on the afm). I don't know if there is such a signal readily available on most carby motors,

An auto elec told me that you can get a 'tachimatic relay' which is closed when it recieves a tach pulse (so it would be wired into your coil) but from what he said they are expensive, apparently found on european cars.

[sillycar chick]

because my CD player is on accessories, and I want the fuel pump to be on "on"

[timbosaurus]

For a "resettable" fuel pump on engine stall etc... you can use a 5-pin relay. Two pins (let's call them pin 1 & 2) energise the coil, providing the switching. The other 3 pins (let's call them 3,4,5) are the higher current switched pins. (one common, one normally open, the other normally closed)

the sequence of running the pump goes like this....

Ignition is off - Ignition wire is low (0 volts) and oil sensor is low (0 volts) so coil is not energised. Therefore the fuel pump is connected to the ignition wire which is off, so fuel pump is not running.


Ignition is switched to 'on' - Ignition wire is hi (12 volts) and oil sensor is still low (0 volts) so coil is energised. Therefore the fuel pump is connected to the start wire which is 0 volts, so fuel pump is still not running.


Ignition is switched to 'start' - Ignition wire is hi (12 volts) and oil sensor is still low (0 volts) so coil is energised. Therefore the fuel pump is connected to the start wire which is on, so fuel pump is running.

Ignition is switched back to 'on' - Ignition wire is hi (12 volts) and oil sensor is hi also (since car is started) so coil now NOT energised. Therefore the fuel pump is connected to the ignition wire which is on, so fuel pump is running.

drive drive drive....

The fuel pump will now stop IF:

Ignition is switched off - Ignition wire is low and oil sensor is hi momentarily before going low. The coil should not be energised in either state. Therefore the fuel pump is still connected to the ignition wire which is off, so fuel pump is not running.


or...

Engine stops/stalls etc - Ignition wire is hi and oil sensor is low. The coil should then energise. Therefore the fuel pump is connected to the start wire which is off, so fuel pump is not running. But it is in the state that is ready for the car to start.

I think i have got the logic right... but i can see me coming back to edit accidental descrepencies in the logic!

[timbosaurus]

I just realised how complicated i made that seem.... sorry

[sillycar chick]

WOW that is way over my head LOL!! Maybe one day I will understand

[timbosaurus]

WOW that is way over my head LOL!! Maybe one day I will understand

Nah, i just can't explain myself very well.

You can simply use a standard 5 pin relay, probably not expensive at all from super steep auto.

If i recall correctly, the pin numbers (which should be labelled) are:
30 - common. Connect this to the fuel pump +ve terminal.
85 - relay coil -ve. Connect this to your oil pressure light.
86 - relay coil +ve. Connect this to your ignition wire.
87 - normally open*. Connect this to your start wire.
87a - normally closed*. Connect this to your ignition wire.

When you switch your ignition to 'on', your fuel pump wont be runnning... until you turn the ignition to 'start'. The the pump will stay on after cranking until you either switch off the ignition, or the engine stalls itself.

explained graphically...

The second relay simply relieves the ignition and start wire of the current required to run the fuel pump

Hard to explain easy... but easy to hook up.

[sillycar chick]

Ahhh a picture is worth a thousand words That is much easier to understand!! THanks!!

My biggest querie is how can I hook up the ignition bit without tapping into the back of the fuse panel with one of those stupid clips? They arent good wiring practise in my eyes, just cause more problems.

[crowncustom]

Most pumps are connected to the positive terminal on the coil.So when you turn your ignition to on it starts pumping but if it was done this way I cant see why a relay could not be incorporated into this.
Cheers Brett.

[o_man_ra23]

Brett, that is required for EFI pumps to prime the lines so theres enough pressure, in a carby car this is not required as your floats take up the slack.

Timbo's wiring setup from an engineering point of view seems quite good. Failsafes are in place, current load is removed from unneccesary points, etc. I would say it would work perfectly.

Tapping into the ignition can be done by using a piece of a screw down terminal strip (about a dollar from dick sniffs). Cut a wire which runs from the ignition, and have one end in the strip on its own, and the other end paired with the wire for your fuel system. Also you can use a second point of strip to do the start wire in the same fashion. This is how ive been doing wiring mods in cars for years, and never once have had a faulty join. Make sure you screw down onto STRIPPED BARE WIRE, and not the plastic insulation.

Cheers, Owen