Underdog Posted June 18, 2015 Share Posted June 18, 2015 Problem: After modification, battery was draining to the point of no-start when car sat for 2+ weeks. Troubleshooting: Follow this thread and included links from the original post quoted below through to resolution. Resolution: In the original modification per this thread and the diagram below, the new relay is getting signal by tapping off the B+ wire that goes to the FPCM. The new relay sends battery power direct to the pump via the FP+ wire, with ground-side switching still being controlled by the FPCM. When the ECU stops commanding the FPCM to drive the pump, the FP- side of the circuit comes up to the same voltage as FP+. Due to the internal circuitry design of the FPCM, the 12V coming direct from the battery through the FP+/pump/FP- can then jump over to the B+ terminal and keep the relay switched, even though power from the stock FP relay (at the other end of the red/black wire) has been removed. In my modification as outlined in this next diagram, rather than tap off the B+ wire I disconnect it from the FPCM entirely, and use it to switch the new relay. The new relay sends battery power direct to the FPCM. This eliminates the voltage drop from the main fuse box #11 fuse to the stock FP relay, and through the long 18ga red/black wire back to the FPCM. Relevant to the original problem, this also allows the new relay to be switched open/closed by the stock circuitry, eliminating the battery drain. With the factory wiring I found ~.75V drop between the battery and B+ terminal at the FPCM. With the new wiring they are within .05V. Voltage at the FP+ terminal is within .05V of the B+ supply voltage, meaning the FPCM is not a significant restriction. I was not able to test the output of the STI FPCM as neither module procured from eBay worked for me. The other key element of this modification is beefing up the FP+ and FP- wires to the pump. By running the 12ga wire in parallel we can be certain the pump is getting as much of the voltage coming out of the FPCM as possible. I did not measure the drop across the original or modified wiring so I don't have numbers for this. Voltage gain from direct feed to FPCM B+ = .7V Voltage gain from 12ga wire FPCM-to-pump = unknown It is important to note that the numbers I observed were during warm idle when the pump is only driven 33% duty cycle. Under 100% duty cycle it is likely that the stock wiring dropped significantly more voltage due to the higher current passing through the wires. This is true for the modified wiring too, but the drop is proportional to the resistance (i.e. triple the current means 2.25V loss from battery voltage on original wiring and .15V on modified wiring). You might be able to get a similar result by soldering in some 10-12ga wire in parallel with the red/black wire from the stock FP relay back to the FPCM, but the passenger seat and carpet would need to be removed to get access to the wire chase. Also, there could be significant voltage drop between the main fuse box #11 fuse and the FP relay, which would be more difficult to resolve cleanly since the wires are tightly loomed and run along the firewall. Original Post said: Hey Folks, I have a bit of a head-scratcher here. Ever since I completed the last round of modifications on my '06 LGT I have had a small drain on the battery (~.1A). This causes a battery voltage drop of ~.1V/day. In the process of troubleshooting I discovered that pulling the FP relay's 30A fuse resolved the issue. I can make this problem occur simply by cycling the key to IGN and switching back off. Once I pull the 30A fuse the relay switches off and does not switch back on when the fuse is reinstalled. Once the contact is broken the current draw drops to ~.01A. I have verified that the wiring between the battery/relay/FPCM is correct. My battery is in my trunk and the wire runs are very short. 12V+ goes from the 30A fuse to Pin 30 on the relay. Pin 87 goes to FP+ at the pump. Pin 85 to chassis ground. Pin 86 to ("B+", red/black) at the FPCM. This has been verified against the instructions here, and in the DW FPHWK install instructions. I have used two different standard 40A/12V SPST relays in the process of troubleshooting. What appears to be happening is, once the connection is made, the current is feeding through the FP wiring and back into the FPCM via the "FP-" where it somehow keeps the "B+" pin hot. Since the FPCM "B+" is the trigger for the relay, it is keeping itself switched. The FPCM is the original from my car. Entirely possible it has an internal fault, although it seems unlikely. I do have a spare STI FPCM I received as a replacement for a DOA unit I bought off eBay, and I can try it. I have tried to duplicate the problem with the FPCM removed and it does not occur. The relay still switches with IGN since it is tapped off "B+" which gets power from the factory FP relay; but when the key is turned off the relay contacts open since there is no back-feed through the FPCM keeping B+ hot. P.S. The car drives fine and if anything is running quite rich (still on break-in map; pulling fuel, but not pegged, in A/F learning A-C). The Crimson Dynamo Link to comment Share on other sites More sharing options...
Underdog Posted June 19, 2015 Author Share Posted June 19, 2015 Tested the other 22750AA010 FPCM - pump will not prime. Relay switches on with IGN (again - getting power off "B+" from factory FP relay) and switches off with key off. Back to LGT FPCM pump will prime and relay stays switched with key off. The Crimson Dynamo Link to comment Share on other sites More sharing options...
Turkeylord Posted June 19, 2015 Share Posted June 19, 2015 I had a similar issue - start here? http://legacygt.com/forums/showthread.php/fuel-pump-control-module-143860.html?p=4569538 Link to comment Share on other sites More sharing options...
Underdog Posted June 19, 2015 Author Share Posted June 19, 2015 (edited) Interesting. I have removed the Green/Yellow wire by removing the terminal from the FPCM connector housing and snipping off the last 3" of wire (and insulating the cut end). My relay switch signal is teed from the red/black ("B+") which is still connected to the FPCM. The only thing left to confirm is that my connections at the pump side are correct. It also seems weird that neither STI FPCM will allow the FP to run but are still receiving power at the pins when key is in IGN. Edited June 19, 2015 by Underdog The Crimson Dynamo Link to comment Share on other sites More sharing options...
Underdog Posted June 19, 2015 Author Share Posted June 19, 2015 I just checked the connections at the pump - everything is correct there as well. The Crimson Dynamo Link to comment Share on other sites More sharing options...
Underdog Posted June 19, 2015 Author Share Posted June 19, 2015 As further proof that it is coming from the power side of the new relay and back through the FPCM I just cycled the key and pulled the M/B #11 (15A) fuse which is for the power side of the factory FP relay (and provides power to the red/black "B+" wire at the FPCM) - no change, relay is still switched. The Crimson Dynamo Link to comment Share on other sites More sharing options...
Benjamin M Posted June 19, 2015 Share Posted June 19, 2015 I believe I experienced/am experiencing the same issue, also having completed the FP/FPCM wiring upgrade. Normal day to day driving I never noticed an issue, but when I would come back from offshore (the car being parked for 15 days) the battery would be dead. I'd jump it and not experience any issues over the 12 days I would be home. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Underdog Posted June 19, 2015 Author Share Posted June 19, 2015 (edited) I am starting to think that everyone with the upgraded wiring may be having this problem, but it is only observable if the car is left undriven for an extended period of time. It is not unusual for me to go 2+ weeks in between drives, which is when I experienced the dead battery. Ever since I discovered that pulling the new fuse stopped the draw I have not had that problem (plus I've been keeping it on a trickle charger since I proved the cause and solution). Here are the internals of my factory FPCM. When I probe between the red (FP-) and blue (FP+) locations there is definitely a connection - with my meter set in the 200kohm range it climbs from about ~35 and settles around ~44. Between the blue (FP+) and green (B+) locations there is a direct and obvious current path. With the key in IGN and probing the inside of the FPCM the FP+ and FP- are hovering right around the same voltage, but with the key off there seems to be a .6-.7V drop between the red (FP-) and blue (FP+) locations, i.e. 12.2V at the FP- and 11.6V at the FP+ and B+. Edited June 19, 2015 by Underdog The Crimson Dynamo Link to comment Share on other sites More sharing options...
Underdog Posted June 19, 2015 Author Share Posted June 19, 2015 I'm going to remove the relay and return the wiring to stock, save for the 12awg wires bolstering the FP- and FP+ (which I will reconnect to the yellow/green wire and reinstall the terminal in the FPCM connector). The Crimson Dynamo Link to comment Share on other sites More sharing options...
Benjamin M Posted June 19, 2015 Share Posted June 19, 2015 Back to stock?! Boo says I. Hmm Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Underdog Posted June 19, 2015 Author Share Posted June 19, 2015 I'm gonna chew on it for a bit - maybe hack up a junk FPCM to better understand the circuitry. I checked the voltage at the FPCM B+ and it was only .05V lower than at the battery. With the uprated wire between the FPCM and FP, and the beefed up ground wire from the FPCM to chassis, I shouldn't be losing too much at the pump. The Crimson Dynamo Link to comment Share on other sites More sharing options...
Underdog Posted June 21, 2015 Author Share Posted June 21, 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. The Crimson Dynamo Link to comment Share on other sites More sharing options...
bigBADbenny Posted June 22, 2015 Share Posted June 22, 2015 Excellent diagram thanks! Link to comment Share on other sites More sharing options...
Scooby2.5 Posted August 24, 2015 Share Posted August 24, 2015 Thanks for this underdog. I recently discovered my car was draining the battery. I never thought about the fact the relay was not turning off. Ill have to look into fixing mine with your new diagram. You saved me some troubleshooting!! Link to comment Share on other sites More sharing options...
Underdog Posted August 24, 2015 Author Share Posted August 24, 2015 Just glad to know I am not the only one! Let us know how it works out for you Greg. The Crimson Dynamo Link to comment Share on other sites More sharing options...
Turkeylord Posted August 24, 2015 Share Posted August 24, 2015 Interesting, so that's a little different than what I did. You're still running the +12 through the FPCM, I'm bypassing it completely. Link to comment Share on other sites More sharing options...
Underdog Posted August 24, 2015 Author Share Posted August 24, 2015 (edited) Yes but if you are switching negative side (FP-) with FPCM then the relay & module is staying powered with ignition off. I originally had it wired per your walkthrough and found FP- feeds back to B+ through the FPCM so the relay would essentially keep itself switched on once the key was cycled, until the in-line fuse to the relay was pulled. Edited August 24, 2015 by Underdog The Crimson Dynamo Link to comment Share on other sites More sharing options...
Turkeylord Posted August 24, 2015 Share Posted August 24, 2015 I don't believe I'm having that issue. The car sat for 9 days a couple weeks ago with no problems. I'll have to take it apart and probe the pins to be sure. The only thing feeding power to my FPCM is the stock Red/Black, switched by the stock fuel pump relay. No additional +12 goes to my FPCM. Link to comment Share on other sites More sharing options...
Underdog Posted August 24, 2015 Author Share Posted August 24, 2015 9 days would be less than 1v drop for me at the battery. It was the 2-3+ week sits that I would start to have trouble. Does your FP- get switched by the FPCM? If so then the 12v from the battery is going through the pump and back into the FPCM on the FP- wire. That is assuming you have it wired per your own walkthrough like I did. The Crimson Dynamo Link to comment Share on other sites More sharing options...
Turkeylord Posted August 24, 2015 Share Posted August 24, 2015 If so then the 12v from the battery is going through the pump and back into the FPCM on the FP- wire. My +12 battery feed is cut by the relay, so there is no positive connection to the pump when the key is off. Looking at your diagram, I'm guessing you didn't un-pin the FP+ from the FPCM plug. Link to comment Share on other sites More sharing options...
Turkeylord Posted August 24, 2015 Share Posted August 24, 2015 Unplug the FPCM plug and remove the Green/Yellow. Pry up the white retainer, then un-pin the terminal.http://i.imgur.com/mSydYWPl.jpghttp://i.imgur.com/8AwVJ5zl.jpg I loomed the harness back up and taped the terminal to it making sure it was well covered after this pic was taken.http://i.imgur.com/jrONDuDl.jpg Link to comment Share on other sites More sharing options...
Underdog Posted August 24, 2015 Author Share Posted August 24, 2015 Nope, I did unpin FP+. I'm telling you, it was wired exactly the same as your walkthrough. Read this thread start to finish, its all here. All you need to do is cycle the key and check if your relay is still switched, then pull the fuse and see if it opens. The Crimson Dynamo Link to comment Share on other sites More sharing options...
Underdog Posted August 24, 2015 Author Share Posted August 24, 2015 Interesting. I have removed the Green/Yellow wire by removing the terminal from the FPCM connector housing and snipping off the last 3" of wire (and insulating the cut end). The Crimson Dynamo Link to comment Share on other sites More sharing options...
Turkeylord Posted August 24, 2015 Share Posted August 24, 2015 My relay opens and closes with the key, no latching problem. I still need to A/B test the STi FPCM. When I do that I will confirm my wiring and power state of the relay and FPCM. I didn't provide an overall schematic in my walk through. SBT did, but I don't think it's 100% correct. Link to comment Share on other sites More sharing options...
Underdog Posted August 24, 2015 Author Share Posted August 24, 2015 I dont recall any discrepancies between your walkthrough and his write-up/diagram. Will be interested to see what you find next time you're in there. The Crimson Dynamo Link to comment Share on other sites More sharing options...
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