Aracheon Posted August 25, 2012 Share Posted August 25, 2012 Exact same issue with the Hella relay, grounding both the FPCM and the relay to the same spot using new wiring. (Tested separately the grounding point at the back of the car, as well as using my 8awg test cable that's hooked directly to the battery.) Results are the same with both modules, except that the voltages on the LGT module are a little lower. Sent from my ADR6400L using Tapatalk Link to comment Share on other sites More sharing options...
Aracheon Posted August 27, 2012 Share Posted August 27, 2012 Update: I ordered another FPCM from an '04 STi which showed up today. Plugged it in, and the voltage behavior I was seeing from before still exists. However - the car was holding fuel pressure at idle without a problem. Took it out for a drive, voltage at the pump didn't change by more than .02v from 33% duty cycle to 100%, but the fuel pressure rose in accordance with boost and the car runs exactly the same as it did when I had the pump wired directly to the Aeromotive relay. I guess I had two bad FPCMs. What I find strange though, is I was seeing the same voltage readings that everyone else was seeing prior to wiring in the Aeromotive relay, and now both of my multimeters (different brands, different ages) are reading the same. Makes me wish lab scopes were cheaper... Because of how much plugging in / unplugging I've done with the fuel pump plug, I also have a replacement rear fuel harness on the way, which I will be rewiring into the car so that the wires and plugs are all clean, fresh, and unscathed. Link to comment Share on other sites More sharing options...
coldsubycz Posted August 28, 2012 Share Posted August 28, 2012 ^ Would it be possible to take a picture of the FPCM and new relay? And a close up picture of the FPCM harness? Link to comment Share on other sites More sharing options...
Aracheon Posted August 28, 2012 Share Posted August 28, 2012 Surely. I'll snap a couple tomorrow morning. Link to comment Share on other sites More sharing options...
Aracheon Posted August 28, 2012 Share Posted August 28, 2012 (edited) Ignore the messy wiring, haven't had a chance to clean it up or label anything yet. From left to right, Working STi FPCM (2nd replacement), bad STi FPCM, bad stock FPCM: Backside of Aeromotive (Tyco) relay: Top of Aeromotive (Tyco) relay: Backside of FPCM harness: Edited April 29, 2023 by Infosecdad Fixed image links Link to comment Share on other sites More sharing options...
coldsubycz Posted August 29, 2012 Share Posted August 29, 2012 The second picture from the top is good! Could you take another picture like the second one, but further back. I'd like to trace your wire routes just to double check for you. It seems like the red wire in the foreground goes directly into the FPCM and not from the "new" relay. Wider angle picture might help. Link to comment Share on other sites More sharing options...
Aracheon Posted August 29, 2012 Share Posted August 29, 2012 (edited) I'll grab one tomorrow when I head out to the shop. But in the meantime, this is how the wires are routed: (Pink = power from battery. Yellow = signal from fuel pump relay. Turquoise = power from new relay to FPCM. Orange = new relay ground. Green = FPCM ground.) http://i.imgur.com/NZBrR.jpg Edited August 29, 2012 by Aracheon Link to comment Share on other sites More sharing options...
coldsubycz Posted August 29, 2012 Share Posted August 29, 2012 ^ Great picture/diagram! I went over my notes on what goes to where and double checked my car... Like you have been saying, it's wired exactly like mine. I was thinking the light green wires were switched, but those are correct too. I'm stumped Only thing I can think of for troubleshooting purposes is to hook it up like stock and see if the same thing happens. Link to comment Share on other sites More sharing options...
Aracheon Posted August 29, 2012 Share Posted August 29, 2012 Returning the wiring to stock would be more work than just taking it to a shop and convincing a tech to hook an oscilloscope up to the FPCM to verify the output signal is what it should be. (That being the only thing I haven't been able to accurately test.) Speaking of, Coldsuby, what multimeter did you use for your testing? Link to comment Share on other sites More sharing options...
coldsubycz Posted August 29, 2012 Share Posted August 29, 2012 I used an inexpensive unit off of Amazon, Mastech digital Multimeter MS8268. Oh no I don't want you to return it to "stock" just take the "87" cable out of the "new" relay and temporarly connect it to the "85" wire "Yellow = signal from fuel pump relay". That way the FPCM is getting its power direct like stock. In essence you are just removing the "new" relay from the equation to see if the FPCM acts like it did before the rewire. Link to comment Share on other sites More sharing options...
Aracheon Posted August 29, 2012 Share Posted August 29, 2012 That appears to be a nicer unit than the one I'm using. Ah - I misunderstood what you were saying. I'll give that a try tomorrow and report back with the results. Link to comment Share on other sites More sharing options...
Aracheon Posted August 31, 2012 Share Posted August 31, 2012 With the newest module in place and the FPCM drawing power from the factory fuel pump relay, the car starts to lose fuel pressure around 15psi and AFRs begin to rise. Drawing power from the Aeromotive relay, fuel pressure rises and holds all the way to 19psi and the car runs like a champ. So I think we can rest easy in that the first replacement FPCM I ordered was bunk. FWIW: Whilst the harness is completely different and won't fit, the 2008-2012 Imprezas (WRX and STi included) use the same fuel pump basket that the 2005-2009 Legacys do. That being said, the PLUG on the Impreza fuel harness is the same as ours. The reason I bring this up, is because I actually wore out one of the retention pins in my factory fuel pump plug removing and plugging in different pins and test wires. I intended to replace the plug in it's entirety, but wasn't able to find a part number for the Legacy rear fuel harness. But I was able to source the rear fuel cord/harness for a 2012 Impreza for fairly cheap, which not only provided me with a replacement fuel pump plug and a few inches of wiring, but also a plethora of replacement PINS. That harness has a bunch of other plugs on it with pins that are the same size as the ones in the fuel pump plug. I've not been able to find a reliable source for the larger crimp pins that Subaru uses in the various plugs and harnesses around the car (except the ECU pins, which IA Performance sells). Through my exercise of soldering 10awg wire to the FPCM harness, I realized it would be incredibly handy to have a few extra crimps pins on hand as spares. The part number for the Impreza fuel harness is 81803FG010, in case anyone ever finds themselves in the same situation I was in. With the new plug and wiring in place, everything sealed up, the car is running like a champ. I plan to take the car in to a friend's shop next week to hook the FPCM up to a lab scope, as my inner geek doesn't like to just let shit be. I want to have concrete and tangible evidence that it's working like it's supposed to, and not just rely on my butt dyno, as it were. Lesson learned: when acquiring junkyard parts, especially electronics, never assume that they work. Scooby 2.5, Coldsubycz, Integroid, and everyone else who has contributed to this thread, thank you for your help. I'd probably still be banging my head against the wall trying to figure out a fuel pressure problem if it wasn't for your input, time, and research. Link to comment Share on other sites More sharing options...
coldsubycz Posted September 1, 2012 Share Posted September 1, 2012 Glad to be of help! All the guys on here helped me out a lot too! Let us know what happens after you use the scope. I've been meaning to ask you this: How did you connect your 10awg wire to the fuel pump? Did you splice in like me or were you able to solder onto the pins? Link to comment Share on other sites More sharing options...
Aracheon Posted September 1, 2012 Share Posted September 1, 2012 During testing I just shoved the wires into the vacancies left by removing the pins from the plug. My first iteration of soldering the 10awg wire directly to the pin didn't work as well as I'd hoped, as the pin holes barely accommodate the wire, much less the wire + the pin. Plus I wasn't very happy with how flimsy everything felt. The final product is the 08-12 Impreza fuel harness. The FP power wires are much thicker than they are on the '05 LGT harness, so I clipped the Impreza plug off about 6" away, and spliced into the thicker wires. Link to comment Share on other sites More sharing options...
Scooby2.5 Posted September 1, 2012 Share Posted September 1, 2012 Yea I never did mess with the wiring from the FPCM to the pump housing itself. The pumps are tested for 13.5-13.7 volts which I was seeing at the pump so I just left it. I may revisit it later and if so Ill probably order your plug. Thanks for the input. Weird you had so much trouble. I find it odd you actually had bad FPCM's Link to comment Share on other sites More sharing options...
Aracheon Posted September 1, 2012 Share Posted September 1, 2012 Yea I never did mess with the wiring from the FPCM to the pump housing itself. The pumps are tested for 13.5-13.7 volts which I was seeing at the pump so I just left it. I may revisit it later and if so Ill probably order your plug. Thanks for the input. Weird you had so much trouble. I find it odd you actually had bad FPCM's I was kicking myself in the ass for messing with the FPCM -> FP wiring in the first place after I started having all the problems, thinking it was something I had screwed up. Even if you look at the Impreza plug wiring, it's still quite a bit smaller than the overkill 10awg wire I'm using. It's probably closer to 14-16. If you can snag that plug out of a junkyard, it would probably be even cheaper than ordering an entire harness from Subaru - but it makes the wiring literally plug and play if you get some step-down butt splices. It's just my luck that I've had this much trouble with the car - it's been a nightmare since day 1. If this had been my first experience with a Subaru, it definitely would have soured me on the brand. Link to comment Share on other sites More sharing options...
coldsubycz Posted September 1, 2012 Share Posted September 1, 2012 Thanks for that part number! In the future I think I'm going to do that as my solder job, 10awg to 18awg is not so good. It's a solid connection just looks really bad. When I first got that STI FPCM and saw the gauge wire the STI uses I was thinking "those lucky bast@#$" . And the use 10awg is over kill to the fuel pump, but it looks bad a$$! So did you just splice all the FP wires onto the new Impreza wires? Because if that is the whole wire harness, doesn't that have wires that go all over the backseat, trunk and up to the front of the car? Link to comment Share on other sites More sharing options...
Aracheon Posted September 1, 2012 Share Posted September 1, 2012 Yeah, I just couldn't deal with it looking like shit. Yep - all 6 wires were spliced into the factory harness. Also yes, that part number is for the complete fuel harness, but it won't work with the Legacy in its entirety. I tried. It doesn't seem to line up. One obvious discrepancy is that the length of wiring from the grommet to the fuel pump plug is WAY too short to work on our car. Link to comment Share on other sites More sharing options...
coldsubycz Posted September 1, 2012 Share Posted September 1, 2012 (edited) Cool! I should have read your previous post better as I could have figured out that you cut/spliced. That's good that they use the 14'ish gauge wire. I still can't believe they use 18 for our car. But why would they, they don't plan on people modify their cars and 18 awg is usually cheaper then 10. Sorry about the stupid questions, but what step-down butt splice did you use for the +/- FP wires? Any if anyone wants to know on Subaruparts.com that harness cost roughly $49. Edited September 1, 2012 by coldsubycz more info Link to comment Share on other sites More sharing options...
Aracheon Posted September 1, 2012 Share Posted September 1, 2012 Yeah, I understand the manufacturing and cost logic behind it, but that certainly doesn't make it any less shitty. I used these ones: http://www.connectorsupply.com/catalog/butt-splice-heat-shrink-step-down-16-14-to-12-10-ga-p-480.html I think I paid $53 for the harness locally with tax. So $49 is in the ballpark. Link to comment Share on other sites More sharing options...
frank_ster Posted September 9, 2012 Share Posted September 9, 2012 i didnt read the whole thread. the pwm for the fuelpump is on the negative only. so if ou ground the ground on the pump the pump will start with the key. ie when the key is in ing position the pump will always run Now that's thinking out of the boxer! fyi all 05 + legacy's have built in code reader Link to comment Share on other sites More sharing options...
Aracheon Posted September 9, 2012 Share Posted September 9, 2012 i didnt read the whole thread. the pwm for the fuelpump is on the negative only. so if ou ground the ground on the pump the pump will start with the key. ie when the key is in ing position the pump will always run Where did you get that information from? (I'm not arguing or saying it's wrong, but I don't remember seeing that anywhere in the vacation pics.) Link to comment Share on other sites More sharing options...
frank_ster Posted September 10, 2012 Share Posted September 10, 2012 from my experence with the buckaru. i had some issues where the fuel pump kept turning off so i got testing. Now that's thinking out of the boxer! fyi all 05 + legacy's have built in code reader Link to comment Share on other sites More sharing options...
coldsubycz Posted September 12, 2012 Share Posted September 12, 2012 I'm a happy guy right now! Just got a message from my tuner tonight: "Well at 6000RPMs, instead of it leaning out to 12.8:1 AFR, I now am at 11.2:1 AFR and the fuel pressure is holding steady where it should be. What power range are we shooting for and how much injector duty cycle do you want to have left for a safety buffer?" I was so worried that my fuel pump was not sealed correctly, but my "little" wiring project worked. Now, do I go 95% IDC or keep it around 85% for safety. (I have ID1000's)(running e85). Link to comment Share on other sites More sharing options...
Scooby2.5 Posted September 12, 2012 Share Posted September 12, 2012 Mine was 92%, congrats Im glad it worked for you Link to comment Share on other sites More sharing options...
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