R33 gtst s2 Fuel pump direct rewire question...

[vxsr33]

Hey guys, im about have a go at the fuel pump relay rewire mod.

I just had a few basic beginner questions, ive had a search but couldnt find anything.

1. The blue wire is the active and the grey is the ground? Is this correct?

2. The blue wire has been cut and joined to purple wires going down towards the right of the back seats. Any idea why this would have been done or what its for?

Thanks guys

[admS15]

There may be a fuel pump kill switch wired in somewhere.

[GTSBoy]

The stupid things people do with speaker wire!

[KiwiRS4T]

Search harder - there are at least two tutorials in the "how to" section.

[vxsr33]

Ive searched and it says the active is light blue and the ground is white.

I have a light blue and a grey instead of white. Im guessing the grey would be the ground, was just hoping someone could confirm.

[GTSBoy]

Have multimeter, will find earth?

[vxsr33]

I don't have a multimeter unfortunately.

[KiwiRS4T]

They are $6 on Ebay. Worth getting as when people have been mucking about with the wiring the colour codes may not tell the true story.

[89CAL]

$20 from super cheap if you dont want to wait otherwise

[GTSBoy]

$10 from Jaycar.

[JustinP]

If you don't have a multimeter, I wouldn't be attempting anything at all. Including making toast.

[vxsr33]

I picked up a multimeter.
How do i find which wire is active and which is ground?

[zoomzoom]

The ground wire will have 0v potential between the wire and the chassis, and also 0 ohms resistance between the wire and chassis.

Actually, a cheapo meter wont be good enough to measure a few ohms or less, but it would be worth checking how much resistance the ground wire has. ie, there may be a couple of ohms in the worst case. No guarantees on the quality of the wire splicing by the looks of things.

[GTSBoy]

The only hassle is that the ground wire is the switched side.  So if everything is off, there will be 12V on the supply wire and on the earth wire.  When the ECU turns on the fuel pump, the relay on the earth wire side will close and go to earth.  As a first step it's easiest to pull the wiring connector off the pump wiring and simply probe the two wires to find which one has 12V.  In the absence of a local plug, you could simply cut all those wires at their joins and work out what's what then put it back together with uprated wiring, pump, etc.

The fuel pressure controller also gets involved in what you measure on the earth side.

[vxsr33]

Thanks for the help everyone. I ended up finding the grey wire was the ground.

So for a r33 gtst s2 (at least mine anyways) the active is the light blue wire and the ground is the grey wire.

I did the fuel pump relay mod with the help of the guides on this forum and some other sources online. I know this is piss easy for some but i have no idea when it comes to wiring and such so it was confusing, but it finally clicked and i enjoyed putting it all together.

Turned the key with fingers crossed and immediately noticed the fuel pump priming was louder. Car started perfectly. Going to neatly tuck away wiring tomorrow and check voltage.

Thanks again guys

[vxsr33]

I was working on the car today and i notice that the car idles rougher at idle with the fuel pump relay mod than with the standard wiring. I measured the voltage with the relay mod and it was 14.2v
Normal wiring is 13.75v

Can the fuel pump relay mod cause rougher idle, im pretty sure ive done it correctly?

[89CAL]

I wouldnt expect so. Is the car tuned or stock ECU?
RB's like running a little richer at idle usually, so wouldnt have expected idle to be effected that bad

[vxsr33]

Car has a power fc however its not fully tuned as the car wasnt getting enough fuel above 10psi on the dyno. Hence me doing the fuel pump rewire to help contribute towards fixing the issue.

[89CAL]

Don't suppose you have an AFR gauge? It may be just enough extra fuel pressure to richen the tune up a little which may have just been enough. Usually I wouldnt think it would be enough to throw out the idle (would have thought so if going leaner) but I'd say that would be your problem. If you have a hand controller, go to the menu that lets you add/take timing and fuel over the whole map (can't remember what it is called, in settings 'inj/ign something' i think) and slowly take some fuel out while it is idling. If this doesnt work then try adding some fuel. See what happens. At idle theres not a great deal of damage you can do

[vxsr33]

Don't suppose you have an AFR gauge? It may be just enough extra fuel pressure to richen the tune up a little which may have just been enough. Usually I wouldnt think it would be enough to throw out the idle (would have thought so if going leaner) but I'd say that would be your problem. If you have a hand controller, go to the menu that lets you add/take timing and fuel over the whole map (can't remember what it is called, in settings 'inj/ign something' i think) and slowly take some fuel out while it is idling. If this doesnt work then try adding some fuel. See what happens. At idle theres not a great deal of damage you can do

Thanks for this, nahh i dont have an afr guage. Disconnected all the wiring from the relay and reconnected. It seems to be running better, im just gonna leave it as is and let the tuner sort it out when i take it it.