How To Direct battery power to fuel pump

J

jsbuds

New Member
Just wondering if the battery is at the front still, what is the best side to run the new live feed down ? Also does the wire have to be 30 amp ???
 
nitrosgti-r

nitrosgti-r

New Member
im deffo going to look stupid here but wires are not my strong point..... but .... when do you need a relay? Why cant you just put a wire from the battery, then to a switch and then to the pump?

cheers
 
V

velly4

Member
If you use a relay you don't have to worry about turning your fuel pump on and off. The relay is switched by the old power supply to the fuel pump so your car works as normal.
 
Fusion Ed

Fusion Ed

Active Member
That post above is an important point. That will shut off the fuel pump if the engine stalls due to crashing etc.. It would take minutes to empty the entire fuel tank if a fuel line split = not good!!!
 
J

jsbuds

New Member
Relays are usually used to switch on a larger current circuit indirectly from a circuit that would not normally be able to handle the required amperage load. Ie ignition uses a similar set up I believe. Please correct if wrong.
 
J

jambo_gtir

Member
jsbuds said:
Relays are usually used to switch on a larger current circuit indirectly from a circuit that would not normally be able to handle the required amperage load
Click to expand...
This is correct. The components on the ECU can only have a small load on them. If you wired your fuel pump directly from the ECU and tried to make the ECU drive it; it would go pop. A relay has a two parts. The coil side can be driven by the ECU as it only requires mA to drive it. On the othere side of the relay is the mechanical contacts that clunk over once the coil is energised (providing it is a mechanical relay and not a solid state relay). These contacts are just metal contacts and can pass a much greater current. Other reasons for relay are for isolation purposes also. You always use some form of isolation or buffer when dealing with external signals to circuit board. That way if you have a fault on the external circuit (fuel pump breaks and goes short circuit) then it has no effect what so ever on the driving circuit (ECU).
Also, relays are good as you can use them across different voltage domains; a low voltage safe circuit (5V) switching on a dangerous circuit (240V A/C).
Hope that helps.
 
Smo

Smo

Active Member
James - would you be able to give me a hand with this please bud? I'm thinking of ditching the swirl pot idea and just having the bosch 044 inline, but would like them both wired up to the battery with relays/fuses (not just for safety, but so that I can pull them out when I'm not using the car so nobody can have away with it). Perhaps we could talk about it and sort out what's required?
 
nitrosgti-r

nitrosgti-r

New Member
Ah right I get it :) it is a pain in the Harris turning the switch on and off but I'm goin to stick with that for a short while until I get time fit a couple relays, as I have a walbro in tank and bosh external, which works well. And for safety reasons I'm opting for relays also :)

Thanks for clearing this up for me
 
STU666V

STU666V

Active Member
Hi all,

I have just fitted a swirl pot and a 044 fuel pump.
The 044 will not turn off when up to pressure like the pump in tank used too? is this because it will never get up to pressure as it goes round the fuel rail then back to the swirl pot then back to tank?

I was checking the volts etc with the car not started but the pump running and when i went to start it it seamed it was flooded a bit as it took a while to start and smelt like a fare bit of fuel coming out the exhaust?

Will the engine be getting more fuel now? i hope not as i just got it mapped, the fuel pressure should just stay the seam and the rest gets returned back to the fuel tank?

I also noticed that the fuel light comes on now? it has over 1/2 a tank of fuel?

I used the black and red wire to switch the relay on.

I might also add an extra switch on the live wire from the battery so i can work on the car if i need the ignition on with out the fuel pump buzzing?

Any answers would be a help ;-)

Ta
 
williams

williams

New Member
Use the live that went to your original fuel pump to activate the relay, then run the live from the battery through the switched terminals on the relay.
 
STU666V

STU666V

Active Member
williams said:
Use the live that went to your original fuel pump to activate the relay, then run the live from the battery through the switched terminals on the relay.
Click to expand...
Thanks,

I might do this?
The thing is i am still using the original + for the pump in tank as i did not want to spilt the new + from the relay to both pumps but i think i will add 2 relays after TOTB as its working just now and have other jobs to do before Thursday night.

Thanks for the info ;-)
 
williams

williams

New Member
the original live to your in tank pump comes from the relay in the engine bay, you could add an extra live coming from that to operate a relay for each pump, or just wire them inline with each other, you could probably even use 1 relay to operate both pumps. but the original live to oe pump is what you need to use to activate the relays, which ever way you choose to do it.
 
williams

williams

New Member
if you use 1 relay to power 2 pumps you may need a higher ampage relay? as 2 pumps will pull more current? im better with practical than electrical theory but i think thats right on, the current rating lol.
 
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