How To: VA Re-Wire Fuel Pump For Constant Voltage

[prestonztt]

Forward:
Tired of those high IDC's and looking for a way of possibly fixing those? Then this is the mod for you! This is an all around good mod from anywhere from a stage 2 car to a big turbo car.

Back in my DSM days, Re-Wiring the fuel pump was a must! The old wires just couldn't handle the high loads when you started making power. The same goes for the WRX/STi. There is quite a bit of flow you can get from just doing this mod.

You can expect for this mod to take about 2-3 hours to complete.

This mod is good for 2002-2007
WRX/STi

Safety:

The install is very straight forward and most anybody can do it. You will be working close to fuel so please be careful. Is is recommended you practice anti static procedures when working in a closed area containing fuel vapor. Prior to entering the vehicle it is recommended you ground your self to the body of the car and keep yourself grounded while working in a vapor ridden area. If available please use a proper grounding wrist strap while working with fuel.


Disclaimer: A word of caution before
attempting any high-performance modifications to your car. This disclaimer is
not meant to incite panic, nor to steer people away from modifications. It's
intended to educate, and to warn. Enjoy your car, feel free to play with it, but
do so with the understanding that ALL mechanical systems are prone to failure.
It's part of the game. I'm not responsible for any damage done while making this
modification

Tools and things you will need:

Disconnect Negative Battery Terminal
NOTE: I'm using butt connectors just for mock up. Soldering is recommended, but crimping is just fine as long as it is done right.
Soldering Iron
Solder
Solder Flux (Optional)
Wire Strippers
Wire Crimpers
Electrical Tape or Shrink Wrap (Your Preference)
Extra 10G Wire
30amp Relay
10G
wire
12G wire
18G wire

or to make life easier:

Summit Racing Fuel Pump Relay Kit: http://www.summitracing.com/parts/SUM-890023/

Note:
I'm using the Summit Racing Kit just because ive used it before and its a nice
piece. If you do not choose to use the kit, here are the where the wires go on
the relay.

Wiring:
30 - Use 10 Gauge wire. Goes to the battery.
87 - Use 12 gauge for less drop. This goes to the Fuel Pump
86 - Use 14-18 gauge. This goes to the car. It is the trigger wire.
85 - Use 14-18 gauge. This is grounded to the car's chassis.

Procedure:

1. Run the 10 Gauge Wire (Red or #30 on the relay) from the trunk to the battery. You will need to add some wire to the relay kit because it doesn't come with enough. I ran the wire on the driver side under the door sills. Up under the dash behind the brake pedal, there is a little rubber grommet. Run the wire through there to your battery.

2. You will need to find a ground (Grey or #85 on the relay) for the relay. There are plenty of places to
put a ground in the trunk, so just take a pick.

3. On the fuel pump harness, we will be working with only 1 Wire and its the Black and yellow one. Snip that wire and make sure you leave enough wire on both ends because you will be soldering them together.

4. Now take the yellow 18G wire (#86 on the relay) on the relay and run it to the harness end of the fuel pump harness. Solder them together then shrink wrap them.

5. Now for your last connection, take the purple 12G Wire(#87 on the relay) and run it to the pump end of the fuel pump harness. Solder and Shrink wrap.

6. Now turn the key to the on position and make sure the fuel pump primes. If it does, then your good to go and its time to clean everything up. If not, go check all the connections and make sure they are where they are suppose to be.

If anybody has any question, comments or anything just let me know and ill try to clear it up for you!

 

[HolyCrapItsFast]

Not to discourage in any way but I have yet to run into a scenario where the wiring for the fuel pump is inadequate. With my tuning and experience as a reference, I have some concerns...

Though you are using the output from the Fuel Pump Control module to trigger the relay, The high frequency duty being supplied to the trigger is not going to transfer through the relay. the relay will simply come on and stay on because it is not fast enough to change states because of its mechanical nature. The only proper way to do this is to use a high speed, high current electronic relay and they can get pretty pricey. Only then will the duty cycle transfer through the relay to the pump along with the additional benefit of added current.

For anyone considering this, what this is doing is bypassing the fuel pump control module and therefore any input from the ECU such as Fuel Pump duty cycle control of the pump speed. Performing this function is like running the pump at 100% duty cycle all the time. The issues this brings up is A.) you require a retune of closed loop fueling because the duty cycle at cruise and normal driving is 33% and 66%. When you run the pump at full speed in these regions of the map you will be very rich and it will show in your fuel trims. B.) This will reduce the life of the fuel pump because it is running 100% all the time and it can potentially over heat and fail.

I think the better solution would be to modify the tune to run your pump at 100% all the time if this is your goal. though I can't imagine a situation that would have you do this other than setups running dual fuel pumps. For any single pump set up, the stock wiring system is sufficient enough.

George

 

[prestonztt]

The pump isn't going to prematurely just "go out". The manufacture doesn't make different modes for fuel pumps. Its just on or off, no in between.

Every time I have done this mod, I have seen IDC's go down significantly. The tune will need to be tweaked a bit, but not a full on re-tune. To get the most out of a bigger pump, this mod needs to be done.

Of course if you are using 2 pumps, then this is a must. I have seen a car almost catch on fire on the dyno from the two fuel pumps putting to much load on those little wires.

 

[HolyCrapItsFast]

I must respectfully disagree with you... the pump absolutely receives a duty cycle signal from the ECU as evidence by the fuel pump controller and the following tables with in the ECU logic, so the pump is variable. During idle and cruise the pump is at 33% capacity and during moderate acceleration it is at 66% capacity. Only during WOT does the pump see 100% steady voltage. You can see this effect by observing the fuel pressure on cold start. In that condition the pump is supplied with 100% duty to allow more fuel and pressure while cold. But when it warms you will observe the pressure to drop suddenly when the ecu goes into closed loop. This is because the duty cycle has dropped to 33%.



I have been doing this a long time. I often use these tables to compensate for idle issues and to improve the spray pattern on larger injectors at idle.

George

 

[prestonztt]

I know there are duty cycles in the ECU for the fuel pump. I was saying that the fuel pump is not going to die early due to it being at 100% all the time.

The stock wires are not sufficient enough to deliver full voltage to an aftermarket fuel pump at WOT. I have meausured a 1.5-2 volt drop at WOT with Walbros and DW300's from WRX's to DSM's.

For the average person, a non-hardwired pump will do just fine. If you want the most out of your pump, then this is the mod for you.

 

[HolyCrapItsFast]

Again I must disagree somewhat... I do not feel there is a need to perform this on single pump setups using most of the after market in tank pumps. For the older amperage hungry pumps like the Bosch 44 and the like, yes it needs it. I am not saying this should never be done. I'm just saying I don't think it should be done for everyone replacing their pump with an after market unit. Before you go hacking into your wiring, understand why you are doing it and what it is going to effect. The readers have a right to know this which is why I am giving my perspective.

None of the tuners I am associated with have done this unless they are running dual pumps and have tuned for it. I my self have never done this and I have never ran into any situation where IDC's where to high as a result of the pump not getting sufficient current. There is also not to much material out there on this and no evidence or real testing to confirm this.

Again I see the value in this mod, only used for the right reason. I would do this as a last resort. :tup:

**EDIT** Just to clarify. With changing voltage to the pump, comes changing output pressure. So the pump will supply more potential fuel pressure if you perform this mod. My argument is that it may not be necessary in every case. The bottom line is if your IDC's are sufficient then leave it alone until it becomes necessary. Your tuner should be the one to make this decision.

 

[prestonztt]

Like I said, this isn't for everyone. 95% of Subaru owners are content with 350whp or less and don't have fueling issues from the fuel pump.

This mod is especially recommended when running E85.

 

[Td_d]

Not only does the ecu logic allow for switching between three modes of fuel pump duty (low, medium, high), there are also tables that can be tweaked as to when the switch between the modes happen. Easier to tweak the ecu tables than rewire.

 

[HolyCrapItsFast]

Not only does the ecu logic allow for switching between three modes of fuel pump duty (low, medium, high), there are also tables that can be tweaked as to when the switch between the modes happen. Easier to tweak the ecu tables than rewire.

Yes I agree, although I believe the crux of this modification is to supply the pump with much needed current and no amount of ECU tuning is going to do that. I definitely see the value in this for very high amperage pump setups such as dual pumps.

However I still maintain the stock wiring is good for single pumps regardless of fuel being used. Example... My old car was pushing near 500whp by the end and that was with a single walbro, 55 psi base pressure, 1000CC injectors and E85. I had no fuel pump issues to speak of. That is just one example of many.

 

[Td_d]

Agreed - duel pump setups are a whole other ball game - but as you say, there's a fair amount you can squeeze out from a single.

 

[fuji_production]

this should remain constant across all single in tank pumps correct? if the amperage draw is consistent? i.e. the dw300 and the aero340?

 

[HolyCrapItsFast]

I believe so. I can only speak from experience though. I would think if you go with something like any single bosch 44 or any performance inline pump, it requires this mod. :thumbup:

 

[STIMULA8]

Was looking for this! Thank you and a great write up :tup:

 

[Subtyper]

I am building a rally car that uses a walbro 255 intank pump to lift fuel to a swirl pot then to a inline filter then to a bosch 044 fuel pump to head upto the fuel filter and fuel rail. Will it be necessary to perform this modification for the Bosch and the itank pump or relay the bosch and use a link lead to trigger the relay rom the original wiring harness.

 

[SubieFan]

I was looking into this mod for my WRX but it looked pretty complex for a wiring layman like myself. Also soldering by the fuel tank kind of freaked me out. I found this cool solution by iWire. It was a little pricey but its PnP and I figure buying the kit and doing it myself was cheaper then bringing it to a shop. Here's a link if anyone wants to check it out https://www.iwireservices.com/product-page/fuel-pump-controller-hardwire-kit

 

[HolyCrapItsFast]

That seems worth it to me. :tup:

I was looking into this mod for my WRX but it looked pretty complex for a wiring layman like myself. Also soldering by the fuel tank kind of freaked me out. I found this cool solution by iWire. It was a little pricey but its PnP and I figure buying the kit and doing it myself was cheaper then bringing it to a shop. Here's a link if anyone wants to check it out https://www.iwireservices.com/product-page/fuel-pump-controller-hardwire-kit