Hardwiring the fuel pump

Doctor G · Post by **Doctor G** » Fri Jun 27, 2008 9:03 am

Okay so the next step is to hardwire the walbro.

Got all the parts from my local midas. Just need to confirm something before I do blow up myself.

I'm using a 4 pin relay. The way I figure it I will connect it as follows:

12v with inline fuse from battery to pin 1 on relay.
The opposite pin from pin 1 (call it pin 3) on the relay goes to the positive terminal on the fuel pump.

Then,
For the trigger on the relay, call it pin 2, I will use the old positive terminal wire that used to power the fuel pump.
And this is what I'm not sure of - do I connect the last pin (call it 4) to Gnd?

How do I decide what size inline fuse to use? I got a 15A but I see the OEM fuel pump fuse is 10A...?

Vlade · Post by **Vlade** » Fri Jun 27, 2008 9:24 am

Your pins have me confused... but simple terms it works like this

2 pins are for Powa, when powa gate closes, that will create a short between the other two pins... if you have a 5 pin relay, you'll have two ways, one that will create a short when it has powa, on the other pin it will break the circuit when you have powa

the relay has a little diagram on it, it will make sense when you look at it...

Figure it out with a 12V battery, can't break the thing, trust me...

Sokar · Post by **Sokar** » Fri Jun 27, 2008 9:32 am

A relay uses a small current to switch a big current right,

So on the control side you will use the old + and - to switch the relay, once its switched you get a "bridge" between the other 2 terminals, so you only "bridging" one of the polls to the pump, not both so connect Ground from the body straight to the pump, and use the relay to only switch positive from the battery to the pump.

Make sense?

Sokar · Post by **Sokar** » Fri Jun 27, 2008 9:32 am

I see Barend got here first

Vlade · Post by **Vlade** » Fri Jun 27, 2008 9:37 am

n00b!

Doctor G · Post by **Doctor G** » Fri Jun 27, 2008 2:31 pm

Cool thanks. Makes sense.

Here are two diagrams. The first one is what I wanted to do as per my initial post.

The second one is Sokar's suggestion.

Anyone on the fuse?

Daniel · Post by **Daniel** » Fri Jun 27, 2008 2:37 pm

can i ask whats the point of this?

Doctor G · Post by **Doctor G** » Fri Jun 27, 2008 2:43 pm

Daniel wrote:can i ask whats the point of this?

Std factory wire is rather thin and also aged by now. SO often your fuel pump doesn't get it's good share of 12-13V, causing it to flow crap.

Having a hardwire setup gives it the best possible voltage to allow for optimum performance. Apparently it's a must on most Nissans. I've heard good things from back to back dyno's with this mod.

Everyone should do it.

Riekert · Post by **Riekert** » Fri Jun 27, 2008 2:49 pm

Doctor G wrote:
Daniel wrote:can i ask whats the point of this?
Std factory wire is rather thin and also aged by now. SO often your fuel pump doesn't get it's good share of 12-13V, causing it to flow crap.

Having a hardwire setup gives it the best possible voltage to allow for optimum performance. Apparently it's a must on most Nissans. I've heard good things from back to back dyno's with this mod.

Everyone should do it.

mmm thanx. Oh and will this also make a diff on the std pump?

Doctor G · Post by **Doctor G** » Fri Jun 27, 2008 2:53 pm

Riekert wrote:
mmm thanx. Oh and will this also make a diff on the std pump?

Yes, provided the pump isn't stuffed to begin with.

Sokar · Post by **Sokar** » Fri Jun 27, 2008 3:35 pm

You can use a common or original ground for the pump like you did in your first pic, but I prefer a nice beefy + and - wire for the pump.