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Upgrading Your Fuel Pump Wiring (4th Gen)


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***Notice***

It has been brought to my attention that this mod as shown may cause a small current drain, possibly due to an indirect ground connection through the FPCM. Please see the following thread for more information:

http://legacygt.com/forums/showthread.php/fpcm-wiring-upgrade-relay-staying-switched-w-key-off-242295.html

 

When I have time to diagnose/fix the issue on my own vehicle I will update this guide.

***Notice***

 

 

 

 

This is a walk through guide to upgrading your fuel pump wiring. The OEM wiring is small and experiences significant voltage drop by the time it gets to the fuel pump. Upgrading the wiring will help deliver more volts to the fuel pump and help it run better.

 

 

For general questions or alternate methods regarding upgrading the fuel pump wiring, please post in this thread!

 

 

 

 

 

This install was done on a 2005 Subaru Legacy GT Wagon, YMMV. Follow these instructions at your own risk. Sorry sedans (not really sorry). :lol:

 

 

 

Step 1: Remove interior pieces. You will need to remove a bit of interior to gain access to the fuel pump (FP) and fuel pump control module (FPCM).

 

  •  
  • Disconnect the battery.
  • Remove the rear seat bottom. It just pulls up from the front in two places.
  • Remove the driver's side seat bolster piece, where the seatbelt lays. There is one 12mm bolt at the bottom, a couple clips, and a tab slides out of the top of the rear trim panel. I left the seatbelt in place and just swung this piece out the door, but you can unbolt the belt if you'd rather.
  • Remove the rear carpet sections. Spare cover, left and right pieces. They should lift out easily.
  • Remove the tray, tools, and spare. Optional, but more room to work.
  • Unclip and flip up the front foam piece, and remove the drivers side foam piece under the carpet.
  • Remove the D pillar cover.
  • Remove the rear trim panel. This is held on by 5 screws and some clips. Screws are located under each of the tie-down hooks, the D pillar, the bag hanger and the tonneau mount. The seatbelt goes through here too, unbolt if you'd like.

Step 2: Gettin' ready. You'll need ~10 feet of wire for both negative and positive leads to get back to the FPCM. I used 10 awg wire. You will also need to get battery power - I used my (yet to be installed) amplifier power wire. You could run another length of 10 awg to the battery, just be sure to fuse it properly.

  •  
  • Remove the fuel pump cover. You'll also need to remove the cover on the driver's side.

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  • Open up the clip holding the harness to the tank, this will give you a little slack.

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  • Unwrap the end of the harness.

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  • Close-up of the stock wiring.

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  • Unmount the FPCM. It's tucked up into the driver's rear quarter.

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  • Harness moved to show the mount. One 10mm nut and a tab that slides.

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  • Free at last!

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  • Close-up of stock wiring.

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4th Gen Legacy GT Fuel Pump Wiring Upgrade - Turkeylord 9-5-2013 w-wiring diagram, parts lists, .pdf

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Step 3: Wiring. You'll need your wire, your soldering iron, and plenty of electrical tape.

  • Fish your wires from one access panel to the other. I put mine in a piece of loom to protect them down there.

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  • Wires near the fuel pump.

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  • Strip windows in the stock FP wiring. The wires you need are the Green/Yellow (positive :rolleyes:) and the Green/Red (negative :rolleyes:).

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  • Strip the ends of your 10 awg wire and tin everything with your soldering iron. Make your connections. I use zip ties for strain relief.

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  • Tape everything well and plug it back in.

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  • Wires on the other side and the stock grommet.

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  • It took some convincing, but with the wires cut at an acute angle, some tape and some spit-lube, I got them through the stock grommet.

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  • Run your wires back towards the FPCM. I followed the stock harness.

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  • Strip a window in the stock negative lead (Green/Red), tin your wires and make your connection. Do the same for a ground lead on the black wire.

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  • Your positive wire will go to a relay. I used a relay socket and salvaged the pins to go onto my new wires. Pin 30 to fused battery power, pin 87 to fuel pump positive, pin 85 to ground and pin 86 to the Red/Black at the FPCM.

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  • Terminate your FPCM ground and relay ground with a ring or fork and ground them. I crimped and then soldered this connection and used a factory ground location.

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  • Unplug the FPCM plug and remove the Green/Yellow. Pry up the white retainer, then un-pin the terminal.

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  • I loomed the harness back up and taped the terminal to it making sure it was well covered after this pic was taken.

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  • Plug your FPCM back it and re-mount it in the quarter. Secure the relay and connect it to fused battery power. After trying to fit the trim panels, I wound up moving the relay to the other side of this panel so it was inside the quarter.

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Put the interior back together, re-connect the battery and that's it! :cool:

 

This mod has been done a number of ways, this is just one of them! HUGE thanks to everyone in this thread for their outstanding work figuring out how to do this. I'd especially like to thank Scooby2.5, KCwagon, Frank_ster and coldsubycz for their helpful posts in that thread!

Edited by Infosecdad
Fixed the images
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Some have upgraded the module itself to an STi module which performs slightly better. Others have also upgraded the factory harness ends to the larger gauge STi/WRX units. All the relevant information can be found in the original thread here:

 

http://legacygt.com/forums/showthread.php/fuel-pump-control-module-143860.html

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I should also mention that if your fuel pump was struggling to keep up on the factory wiring, this upgrade may affect your tune!

 

I sent new logs to Bren after the upgrade to see if it made a difference, he replied:

 

HAHA wow, yeah it went pig rich.
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This mod is definitely a "must" - to get the fuel pump voltage where it should be.

 

I like the way you color-coded your zip ties to the wires :)

BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT
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Can I add one thing to this.

 

Please please do not use electrical tape to cover wires. Over time moisture will build up(yes even indoors) and it will corrode the wires. Please use Heatshrink tubing to help cover wires. Or if you are going the tape route use some really thick glue and cover the soldered joints to protect from moisture.

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I might add also that 12ga wire is plenty big enough from the battery and also over to the pump.

 

I just purchased the kit from DW and it was pretty good. Had a socket for the Relay, the really had a tab to bolt it to the FPCM bolt and also had a fuse holder in the batter feed.

 

http://www.deatschwerks.com/products/accessories/fuel-pump-hardwire-installation-kit-detail

 

A lot of guys are using 10 gauge which is more expensive and overkill really.

The wiring in a stock STI which doesn't have this problem is around 14 gauge near as I could tell.

 

For those that want to remove the pins, you can go to the original thread and there is information on removing the pins from the connectors which is pretty easily done and then you can solder right on the pin.

Edited by Scooby2.5
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Great point. Just doing a little exercise in the maths...

 

Assumptions: 30' of wire in the circuit, DW65c pulling 11.65A@45psi, 13.8V alternator voltage, ignoring connection losses. You could expect to see:

 

18awg: 11.84V

14awg: 12.95V

12awg: 13.25V

10awg: 13.45V

 

So even with 14awg you'd pick up over 1V. I had the 10awg Green/Yellow laying around so I went with that.

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Making this up into a .pdf - will likely include some info re extracting pins and reusing as well.

 

But, what I didn't see, was any mention or info (P/N, Version, etc.) about the replacement FPCM itself. Are you just using the stock FPCM and rewiring or did you update to an STI one? Too blind to read the P/N on the pic so any help is appreciated... :)

- Pro amore Dei et patriam et populum -
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I'm using the original LGT module. Part numbers for STi modules are listed in the other thread, however there is some discrepancies in which year STi and what part number people are using.

 

IMHO, the wiring is the main problem with the system.

Edited by Turkeylord
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I'm using the original LGT module. Part numbers for STi modules are listed in the other thread, however there is some discrepancies in which year STi and what part number people are using.

 

IMHO, the wiring is the main problem with the system.

 

Actually the STI module you want to use is the 2004-2007 WRX and STI. If you look in the first few pages of the other thread I believe Unclemat found that the 2008 up WRX uses the the same module as the legacy. We also put up a listing of the cars using the older style.

The interesting thing is the older module was like $300 from Subaru and the newer one is $90

We were buying ours used off eBay or NASIOC.

 

I also with the help of Calvin Dotson the tuner for Cobb Plano, found that the stock module even if directly powered from the battery would output only around 12.5-12.7 volts.

The WRX/STI module would output 13.7

Edited by Scooby2.5
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Yep, good news is a lot of cars used the expensive one so it may not be too difficult to find at the salvage yards

 

Someone needs to test the 08 one with batt/alt voltage running to it and see what comes out.

 

IMPREZA

'02, October —SEDAN2500CC EMPI DOHC TURBOFulltime 4WD6SP Manual transmissionSTINormal suspension

'05, April —SEDAN2500CC EMPI DOHC TURBOFulltime 4WD5SP Manual transmissionWRXNormal suspension

'05, April —SEDAN2500CC EMPI DOHC TURBOFulltime 4WDAutomatic transmissionWRXNormal suspension

'06, June —SEDAN2500CC EMPI DOHC TURBOFulltime 4WD5SP Manual transmissionWRX-TRNormal suspension

'06, June —SEDAN2500CC EMPI DOHC TURBOFulltime 4WD6SP Manual transmissionSTI LIMITEDNormal suspension

'05, April —WAGON2500CC EMPI DOHC TURBOFulltime 4WD5SP Manual transmissionWRXNormal suspension

'05, April —WAGON2500CC EMPI DOHC TURBOFulltime 4WDAutomatic transmissionWRXNormal suspension

 

 

FORESTER:

'03, January — '05, MarchWAGON2500CC EMPI DOHC TURBOFULLTIME 4WDManual transmission2.5XTNormal suspension

'05, January —WAGON2500CC EMPI DOHC TURBOFULLTIME 4WDManual transmission2.5XTNormal suspension

'03, January — '05, MarchWAGON2500CC EMPI DOHC TURBOFULLTIME 4WDAutomatic transmission2.5XTNormal suspension

'05, January — '06, MarchWAGON2500CC EMPI DOHC TURBOFULLTIME 4WDAutomatic transmission2.5XTNormal suspension

'06, February —WAGON2500CC EMPI DOHC TURBOFULLTIME 4WDAutomatic transmission2.5XTNormal suspension

'07, February —WAGON2500CC EMPI DOHC TURBOFULLTIME 4WDManual transmissionFORESTER SPORTSNormal suspension

'07, February —WAGON2500CC EMPI DOHC TURBOFULLTIME 4WDAutomatic transmissionFORESTER SPORTSNormal suspension

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Well the verdict is the STI/Impreza fuel pump module was able to plug right into the LGT harness.

 

Bad news is the STI module only output 11.9 volts. .2 more than the stock legacy module using the small stock wiring harness.

 

 

Good news is that if you bypass the stock wiring harness, that seems to drop 1.7-2 volts, with a direct battery feed the STI/Impreza module outputs 13.5 volts to the pump. (This voltage is also determined by how good your alternator output is)

 

If you bypass the wiring harness on the legacy module we would only get 12.5 volts.

 

So it looks as though the STI/Impreza module does output a bit more voltage on max than the legacy module does if the voltage into the module is correct or more..

 

With 13.5v going to the pump now by bypassing the harness with a wire and another relay and using the STI/Impreza module they were able to tune my car to 385WHP 425WTQ on the ID1000 injectors and FMIC. The IDC was around 90%

Edited by Scooby2.5
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Lastly I would say if your alternator is weak, and will only output 13.5-13.8 volts which is common on a Subaru, then placing a diode in the ALT Sensing line will bump the output up to 14.2-14.5 like it really should be.

 

Thanks Frankster and KCwagon for finding this tip!

 

 

http://www.scoobymods.com/showthread.php/raise-your-alternator-voltage-10547.html?amp

 

 

 

I just did this mod with the MK3 PTC diode fuse from Australia. They have been doing this for years on the japanese imports.

 

Notice he has added Subaru to the list as I ordered and installed one of these MK3 diode/PTC fuses.

 

 

http://www.hkbelect.com

 

If you email this guy he will give you a discount

 

 

Here is a thread on NASIOC and this will for sure help the fuel pump voltage issue, although wiring should still be changed etc.

 

http://forums.nasioc.com/forums/showthread.php?t=1602651

 

My alternator voltage is around 13.8 when warm. By the time the voltage drops through the circuits in the car I was low.

 

Now I am putting out 14.5 pretty much all the time.

 

I have a AGM braille battery which when fully charged should be 13.8 volts, 12.6 at rest.

 

It needs 14.5-14.7 to charge it properly according to braille. After doing this mod my battery is 13.84 when car shut off and 12.6-12.8 after resting. I am sure my pump is now running easily 13.5 volts.

Edited by Scooby2.5
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So the consensus is that by upgrading the 12V (+) power supply side wiring (from the battery to the replacement STI FPCM), and only the (+) and (-) wires between the FPCM and the fuel pump, that a relay in the circuit is not "required"? Edited by SBT
- Pro amore Dei et patriam et populum -
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The wire to the B+ terminal is switched with the key, not sure what drain there might be wired direct.

 

I did not try running the upgraded positive side through the FPCM. It goes: battery->relay->pump. Only the negative side goes through the FPCM as that's where the PWM duty cycle operation occurs.

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Okay - reread everything again (both threads) and see the relay in the discussion. Not sure how I missed that :spin:

 

Think I'm just going to get the STI FPCM and the DW "kit" and call it a day. Any suggestions, or how-to, to best run the (+) 12V supply from the battery back to the relay/FPCM location?

- Pro amore Dei et patriam et populum -
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So the consensus is that by upgrading the 12V (+) power supply side wiring (from the battery to the replacement STI FPCM), and only the (+) and (-) wires between the FPCM and the fuel pump, that a relay in the circuit is not "required"?

 

Yes you have to have a relay so power is not live to the pump all the time.

This relay needs to be switched "on" by the red and black wire coming from the original fuel pump relay.

 

I ran the pos batt wire through the firewall at the rubber plug in the middle of the firewall near dog bone.

 

From there across to driver kick panel area and then down the side of the car. The carpet is held down with the black trim pieces and if you just pull on them they pop off. You will see the factory harness there and just run along with it.

Once you get to the back seat area just follow wiring harness to the back of the car where the FPCM is. You will place the relay there. Then from the relay back to under the seat and over to pump via rubber grommet on drivers side access, then below floor to the pump access.

Edited by Scooby2.5
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Okay - reread everything again (both threads) and see the relay in the discussion. Not sure how I missed that :spin:

 

Think I'm just going to get the STI FPCM and the DW "kit" and call it a day. Any suggestions, or how-to, to best run the (+) 12V supply from the battery back to the relay/FPCM location?

 

Exactly what I did. Here are some pics of DW kit already run and a pic of one of the pins soldered on a wire (hadn't shrink wrapped it yet).

 

I like how the DW kit has a relay socket and also a metal loop on the back to use the FPCM nut and bolt to mount it.

 

I used yellow and red wire. Yellow for the Green/Yellow wire to the pump and Red for the Green/Red wire to the pump. All 12GA

 

Also SBT the red wire coming from the battery may seem a bit short if you have a wagon but the length of wire on the socket allows it to be just long enough

IMG_1897.thumb.jpg.807066b8a8542670df5fe79be8399707.jpg

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IMG_1895.thumb.jpg.290d7b9a93516cd184cc0e9023b6490c.jpg

Edited by Scooby2.5
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Not enough .pdf space allocation here so posted the .pdf on ScoobyMods. Thanks for all the work running the individual pieces to ground and to Turkeylord for documenting everything so well with photos and write-up. LMK if I missed anything.
- Pro amore Dei et patriam et populum -
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