fuel pump wiring on mbe/dta/emerald etc. ecus

[peester]

*EDIT SEE PAGE 2 FOR THROTTLE POT HELP*

hi just wanted to check how you wire a fuel pump up when using programmable engine management..
ive got a wire from the ecu thats labelled fuel pump, so just connect it to the positive going to the pump...?
no relays??

[Adam]

Whats the wire output? 12V? Ground??

[peester]

dunno acutally lol..
should be 12v

[peester]

it is a 12v switched live.. so that needs to go into a relay then, then output relay to pump...?

[novacabrio]

there are wiring diagrams on the DTA site

[phazer]

You sure it's 12v switched? Most are switched to ground (DTA certainly is).

Swtiched to ground makes it easy as you can wire it direct to the same pin on the fuel pump relay as the original ECU. Then you don't need to alter any existing ignition wiring/fuses etc.

What ECU are you using? Do you have a diagram - if so I'll take a look for you.

[peester]

http://www.sbdev.co.uk/Engine_Management_Systems/ECU_Details/MBE9A4/MBE9A4_Fuel_Pump.htm

[peester]

its similar to this.. ive circled the connection i mean..
http://img.photobucket.com/albums/v11/peester/wiringloom.jpg

[Adam]

Looking at that SBD link it sounds like you will just need to put that "fuel pump" wire to the earth on the fuel pump.
The other wire on the pump to an ignition live.

The ecu then switches the wire to ground, turning the pump on because the mbe loom already has a fuel pump relay....

(assuming most mbe looms are the same)

[peester]

i think you right ad.. this is what was confusing me..
i going to do one more thing and disconnect the connection ive made and read the wires separately (multimeter)..

[phazer]

Yep as I thought it's a switched neg output. You *need* to run it via relay as per the SBD instructions otherwise you could fry the ECU if the lines get blocked etc (any situation where the pump is pulling a lot of current).

If you still have the OEM fuel pump relay wired in use that and you have everything you need already.

[peester]

ok ill take another look today shortly.. like ad pointed out the 'relays are built in' bit confusses a little too.. i might not need to do it..?

[phazer]

Yes, just has another look, if yours is an SBD loom then it has the relay built in. Looking at the SBD info it's as clear as mud. I can only assume that it will still result in the ground being switched - this makes sense as you may be running heavier duty cable (or some other wiring arrangement to get 12V) to the pump.

You can still just wire this to the original fuel pump relay you'll just have two relays instead of one which isn't a problem.

[peester]

got an answer , in the end i spoke with the chap at gwr that made the loom.. i was right it is a swtiched +, as it has the relay built in so its ready to just plug n play kinda thing.
The fan output wire is what has been said above tho, and ive yet to do that so at least this brainstorming has helped for that one..

[phazer]

Nice, backwards then lol

Essentially you've got a piddly little wire to supply your fuel pump.

A lot of people uprate their 12V supply to the pump using heavier guage cable than factory. To do this you're going to need another relay anyway.

[peester]

yeah we did mention this.. i do have a walbro i planned to fit so i need to check if its over 10amps or not, really..

[phazer]

In that case I'd go with convention and wire the pump heavy guage (regardless of the current draw, it just makes sense) for the 12v and use a relay fed off your loom to switch the ground on the pump. Sorted :)

[peester]

*THROTTLE POT HELP*
How do i find the voltages of the 'pot when closed/open..?
Im supposed to 'set it' at 0.29v @ idle and 4.41v @ full throttle

http://img.photobucket.com/albums/v11/peester/Photo0029.jpg

Ive fitted the pot to the itb's and just cant get my head round how it works..
Any help would be great.

[phazer]

You have PM

Short version:

Tighten pot enough that it holds but can be tweaked a bit.
Put multimeter on pins for signal ground and wiper
Adjust position until idle voltage correct
Tighten pot fully
Check full throttle reading
Adjust throttle stops appropriately to give FT voltage

[peester]

ok, if i cant get this to work.. then i must be **** lol

[phazer]

lol you'll sort it :thumb: