Turkeylord Posted August 24, 2015 Share Posted August 24, 2015 Looking at his diagram again I do think it is correct, the only thing different from my install is wire colors. Not sure where the FPCM would be getting power other than the factory fuel pump relay. The FP+ is disconnected from the FPCM, so it can't back feed from there. The relay coil is the only other thing connected, and there's no way that should back feed power, it's only connected to ground on the other side. Link to comment Share on other sites More sharing options...
Underdog Posted August 24, 2015 Author Share Posted August 24, 2015 (edited) The FP- terminal and B+ terminal on the FPCM are connected internally via the circuitry, see post #8. You can remove the module and test for continuity across the terminals to verify this. 12v was going through the pump via the FP+ wire and back into the module via the FP-, where it jumped to the B+ and kept the relay switched on. Edited August 24, 2015 by Underdog The Crimson Dynamo Link to comment Share on other sites More sharing options...
Underdog Posted August 24, 2015 Author Share Posted August 24, 2015 Here's a diagram I made by memory of the original modification, to illustrate how the 12V from the power side of the relay is getting into the module. Once the ECU stops instructing the FPCM to ground-switch the pump, the FP- side comes "up to" whatever voltage is at the FP+. Since the FP+ is at battery voltage, that is what the FP- "becomes". The circuitry inside the FPCM connects FP- and B+ in some way that keeps 12V applied to the signal side of the relay, keeping it switched. Not a circuit designer, but I would suspect that the FP+ is connected to FP- in some way that allows the duty cycle to be monitored/controlled, and that is how the voltage is "jumping". The Crimson Dynamo Link to comment Share on other sites More sharing options...
Scooby2.5 Posted August 25, 2015 Share Posted August 25, 2015 I ended up with a slight variation of the wiring that resolved this issue for me. Instead of tapping off B+ to feed the FP+ wire directly, I cut the B+ wire and use it to trigger the relay and feed battery voltage direct to the B+ terminal on the FPCM. The FP+, FP-, and E wires are all left intact from the factory, with new 10-12GA wire soldered in parallel to the stock wires. Basically this repurposes the red/black B+ wire from power to signal for the new relay. With the conventional wiring I observed a drop of ~.75V between the battery and B+ terminal at the FPCM. Granted, I have the battery in the trunk so the power had to run to the front of the car on the main 1/0GA wire before going through the main fuse box, to the relay, and back to the FPCM. However, I think it is safe to assume that the long run of 18GA red/black wire was the primary contributor to that voltage drop. With the standard LGT FPCM I observed ~.05V drop between the B+ and FP+ terminals. Neither STI FPCM worked for me. With the new wiring I see ~.05V drop between the battery and FPCM B+, which combined with the .05V drop inside the FPCM means my pump is seeing just .1V less than battery voltage at all times (well, less any losses along the 12GA wires I ran in parallel to the pump). Furthermore, when the key is switched off, the power to B+ from the factory relay is removed, switching off the new relay. I have verified that the drain on the battery has been eliminated. Attached schematic of my version of the mod. Big thanks to all who pioneered this before me. It seems to me from your drawing all you did was disconnect B+ from the module. So B+ is removed and that signal is just feeding the relay and not the module? Not sure what you meant by feeding FP+ unless you had done what turkey lord had done in post 564-569 here http://legacygt.com/forums/showthread.php/fuel-pump-control-module-143860p38.html Link to comment Share on other sites More sharing options...
Scooby2.5 Posted August 25, 2015 Share Posted August 25, 2015 post 65 shows SBT wiring diagram he drew for the forum members http://legacygt.com/forums/showthread.php/upgrading-your-fuel-pump-wiring-4th-gen-213570p5.html Link to comment Share on other sites More sharing options...
Scooby2.5 Posted August 25, 2015 Share Posted August 25, 2015 (edited) Never mind I see what you did. Only feed from stock FP relay to new relay coil. Then Feed B+ with new relay which is direct from battery and wire from FP+ to the pump. Ill check mine out. Good find! Makes since that B+ is straight to FP+ internally as really the module is only pulsing the negative signal, changing the ground reference Edited August 25, 2015 by Scooby2.5 Link to comment Share on other sites More sharing options...
Scooby2.5 Posted August 25, 2015 Share Posted August 25, 2015 Just glad to know I am not the only one! Let us know how it works out for you Greg. My car is currently at Cobb Plano TX getting a new motor. Im picking it up this thursday so maybe next week I can fix the wiring. Again thanks for researching this. I drive my car every day but noticed that if I let it set for a few days it would start but I could tell something was draining the battery. Link to comment Share on other sites More sharing options...
Scooby2.5 Posted August 25, 2015 Share Posted August 25, 2015 BTW my next mod will be the 2015 rack Link to comment Share on other sites More sharing options...
Underdog Posted August 25, 2015 Author Share Posted August 25, 2015 Updated the OP with the resolution and differences between the original mod and my variation. Tried to be as concise as possible. I also put both schematics side-by-side for easier reference. Keep in mind I have my battery in the trunk, so my new power feed and relay is a very short run. People running the new power wire from the engine bay may have a higher voltage drop than my .05V. Greg - make sure you post up your STI rack swap impressions in my rack thread! I am sure you will love it especially coming from the slow OBXT rack. The Crimson Dynamo Link to comment Share on other sites More sharing options...
Scooby2.5 Posted August 25, 2015 Share Posted August 25, 2015 Will do man, and I found the rack for 525 Also i cant find anywhere that you posted your 1.5xtr results Link to comment Share on other sites More sharing options...
Underdog Posted August 25, 2015 Author Share Posted August 25, 2015 That is a great price. Used? That is a good deal less than wholesale. Haven't put the 1.5xtr on the dyno yet - still racking up miles to break in the new engine and clutch. The Crimson Dynamo Link to comment Share on other sites More sharing options...
Turkeylord Posted August 25, 2015 Share Posted August 25, 2015 - The plot thickens - So I realized it would be easy to check mine, as the pump is the only thing on my circuit breaker under the hood. When I cycle the key to run I see ~8.5A on my cheap-o Harbor Freight multimeter as the fuel pump primes the lines, then it drops to 0mA. However when I turn the key to off, I see 120mA. Maybe there is some sort of floating ground problem with the FPCM. For easy maths lets say you have a 60Ah battery - at 120mA draw that's 500 hours aka nearly 21 days. Pretty consistent with the idea that you're having issues and I'm not. I will still have to find out exactly where that 120mA is going - FPCM, relay, or pump. More sleuthing to follow... Link to comment Share on other sites More sharing options...
Scooby2.5 Posted August 27, 2015 Share Posted August 27, 2015 That is a great price. Used? That is a good deal less than wholesale. Haven't put the 1.5xtr on the dyno yet - still racking up miles to break in the new engine and clutch. brand new Link to comment Share on other sites More sharing options...
Underdog Posted August 27, 2015 Author Share Posted August 27, 2015 TL: I assume you are waiting until all lights go out, doors closed, and the BCM goes to sleep (~20sec)? If so that is essentially the same draw I was having when my relay was staying latched. Let us know how it turns out. The Crimson Dynamo Link to comment Share on other sites More sharing options...
Turkeylord Posted August 27, 2015 Share Posted August 27, 2015 No, but I was just measuring the fuel pump lead. I'll dig more for sure. Link to comment Share on other sites More sharing options...
Underdog Posted August 27, 2015 Author Share Posted August 27, 2015 (edited) So this is the lead from the battery to the power side of the added relay? If so, once you are seeing the 120ma, what happens if you break the circuit and then reestablish it? It might make sense that the "new" circuit can draw 0ma with key on and system primed (pump off) if the B+ is at the same potential as FP- and the draw to keep the relay latched is going through the original circuit (M/B #11 fuse). Path of least resistance = the one that doesn't go through the pump and FPCM. Edited August 27, 2015 by Underdog The Crimson Dynamo Link to comment Share on other sites More sharing options...
whitrzac Posted October 17, 2015 Share Posted October 17, 2015 This should be stickied.... I didn't get current measurements, but setup the way the 'guide' shows my battery would drain in about a week of non driving. No issues after changing to underdog's setup. Link to comment Share on other sites More sharing options...
Turkeylord Posted October 19, 2015 Share Posted October 19, 2015 I added a big red ***Notice*** to my thread, with a link back here. Link to comment Share on other sites More sharing options...
dr20t Posted January 18, 2016 Share Posted January 18, 2016 Was pointed here after complaining about my battery life to a local forum member. I have been through two batteries in the last 12 months. I put it down to it being a small battery and due to it not being driven very often. Great pickup underdog. Question - I popped a p230 error code on the weekend (fuel pump circuit), putting me into limp mode. Was about 20km from home so switching on and off allowed me to get home. It was intermittent and not constant. Any chance the current draw with vehicle off for a consistent period of time couldve fried the fpcm? The car gets driven once or twice a month and more recently sat for almost 3 months undriven. Mick Link to comment Share on other sites More sharing options...
Underdog Posted January 18, 2016 Author Share Posted January 18, 2016 Tough to say if the draw could have fried the FPCM, but it's not much of a stretch to imagine the possibility. For P0230 I would verify battery voltage at the B+ pin, resistance between GND and (-) terminal on the battery, and verify the FPCM and pump connections are good, including any solder/crimps you added. How is (was) your system wired when you got the CEL/DTC? The Crimson Dynamo Link to comment Share on other sites More sharing options...
dr20t Posted January 19, 2016 Share Posted January 19, 2016 Tough to say if the draw could have fried the FPCM, but it's not much of a stretch to imagine the possibility. For P0230 I would verify battery voltage at the B+ pin, resistance between GND and (-) terminal on the battery, and verify the FPCM and pump connections are good, including any solder/crimps you added. How is (was) your system wired when you got the CEL/DTC? Thanks for that. Would explain as this battery has been dead and not holding charge after jump starting. System wired per original thread in your original post. Will pull the multimeter out this week sometime and have a dig around Mick Link to comment Share on other sites More sharing options...
dr20t Posted January 24, 2016 Share Posted January 24, 2016 Update - checked entire system to find fuel pump negative inside the cradle was loose on the pigtail plug (walbro 460). This explains p0230 code. After failing to unpick the terminals from the plug to avoid wiring joints in the fuel pump cradle, I soldered and heat shrunk the connection to ensure it was solid. Then took the time to make the upgrade per Underdog's diagram. Im using the same 12ga fp+ and fp- wiring except now the fp+ is fed from the fpcm. Again due to a failed unpicking of the terminals, i had to cut the original wiring about 1 inch from the fpcm plug and soldered the B+ from the relay and the FP+ output to fuel pump onto the original 18ga wires. Voltage at pump tested at 12.2v with ignition priming circuit. This is with a brand new battery showing 12.55v at battery post static. Hopefully the wiring is adequate to cope with 16amp draw the walbro is pulling at 80psi Thanks again for the heads up Mick Link to comment Share on other sites More sharing options...
CapnJack Posted March 19, 2016 Share Posted March 19, 2016 Glad I found this thread. I didn't drive my LGT two years ago all winter and when I went to start it, I found my Optima Yellow Top was bad. It couldn't be revived! I put a new Red Top in and it drained too. I had just kept a trickle charger on it until I could dig into it. It all started after I did the wiring upgrade. I made the changes from this post this morning and all seems to be well. Thanks for this and the research done to find the issue!!! Link to comment Share on other sites More sharing options...
Underdog Posted March 19, 2016 Author Share Posted March 19, 2016 Awesome! Glad it worked for you. The Crimson Dynamo Link to comment Share on other sites More sharing options...
RooTBeeR Posted April 13, 2016 Share Posted April 13, 2016 Finally got around to installing my fuel pump rewire kit. Thanks underdog! Your diagram made it quite easy. "Build" Thread <--Link (OLD) '05 EJ255 now a '13 EJ257 Bottom End w/D25 heads (NEW) Forever Slow [sIGPIC][/sIGPIC] Link to comment Share on other sites More sharing options...
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