CornerHard Posted February 24, 2008 Share Posted February 24, 2008 A bit of a dumb question, but I haven't found the answer yet by scouring the FSM or searching around here: Where does the power wire to the fuel pump come from, and how is it wired? Today my fuel pump stopped working, and testing voltage at the fuel pump showed that it would get just a tiny blip when starting to crank the engine, then go back to 0V. Does the power come directly out of the Fuel Pump Control Unit? Quote Link to comment Share on other sites More sharing options...
MilesFox Posted February 24, 2008 Share Posted February 24, 2008 there is a relay above the steering column directly above the ecu. the BROWN one it will trip with a signal from the ecu caused by a pulse from the distributor. if you plug in the green test (static timing) clips the pump/relay will cycle onand off every 2 seconds. if the test clips prove to work, then you need to look at the distributor, mainly to see if it is turning or not(broken timing belt) turnong the key to the on position will kick on the pump for a second until it sees a signal from the disty to keep going it is possible the fuel pump is getting voltage but is not grounding. the ground side ties in withthe rest of the body ground. you can jump a new wire directly to the body if it is necessary Quote Link to comment Share on other sites More sharing options...
Skip Posted February 24, 2008 Share Posted February 24, 2008 It is a total guess not knowing what car/year/fuel system could be a rev sensor (control unit) could be a relay could be?? The system most prevelent is a relay controled by the ignition switch. The ground being provided by the ECU You say "control unit", I don't think you have an ECU. ????? Why do so many people these days think we know what car their working on?? Quote Link to comment Share on other sites More sharing options...
brokebill Posted February 24, 2008 Share Posted February 24, 2008 Why do so many people these days think we know what car their working on?? ______________________________ you mean youre not omnipotent?! Quote Link to comment Share on other sites More sharing options...
Skip Posted February 24, 2008 Share Posted February 24, 2008 No Bill it's not that. At my school of higher learning, Mind Reading 101 will not be offered until next semister. ;^) Quote Link to comment Share on other sites More sharing options...
brokebill Posted February 24, 2008 Share Posted February 24, 2008 just dont let our incompetence sour you! Be a lot of us walking within a month! Quote Link to comment Share on other sites More sharing options...
Cougar Posted February 24, 2008 Share Posted February 24, 2008 I assume the OP is working on his '83 Soob which is stated in his profile area. It is easier when they state what it is in the first part of the post though. I made a reply to this in post #25 of another thread. http://www.ultimatesubaru.org/forum/showthread.php?t=82917&page=3 Quote Link to comment Share on other sites More sharing options...
CornerHard Posted February 25, 2008 Author Share Posted February 25, 2008 Sorry, it is indeed the 83 GL wagon listed in my profile, and no, I don't have a timing belt I thought the FPCU was a black box above and behind the hood release? Quote Link to comment Share on other sites More sharing options...
CornerHard Posted February 25, 2008 Author Share Posted February 25, 2008 Ok, I traced the fuel pump wiring back to the FPCU, and it was having the same issue at the source - the voltage blips to about 3v when you start cranking the engine, then it goes back to 0v. I tried wiring the black power wire from that connector directly to the fuel pump wire, and with 12v, the fuel pump started working normally again. I assume this means my FPCU is bad? Quote Link to comment Share on other sites More sharing options...
Cougar Posted February 25, 2008 Share Posted February 25, 2008 It does sound like it is bad. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted February 25, 2008 Share Posted February 25, 2008 Could still be the ignition switch as well. Sometimes they have a "sweet spot" that if you go past voltage will stop flowing. Also could be ignition related - if you aren't getting spark, then there will be no tach signal, and the FPCU will not power the pump. GD Quote Link to comment Share on other sites More sharing options...
Cougar Posted February 25, 2008 Share Posted February 25, 2008 Checking for voltage at the coil will tell the story there. Quote Link to comment Share on other sites More sharing options...
newsoobdude Posted February 25, 2008 Share Posted February 25, 2008 At my school of higher learning,Mind Reading 101 will not be offered until next semister. ;^) Yeah, I've failed that class more times than not yet everyone at work thinks I gradiated with honors in it Good info to know everybody, unfortunately, I have no input though on the situation, just knowledge gained. Quote Link to comment Share on other sites More sharing options...
CornerHard Posted February 25, 2008 Author Share Posted February 25, 2008 Thanks for all the tips guys (and GeneralDisorder - I'm amazed that you always have something useful to say in every one of these troubleshooting threads I've posted on ) I have 12v at the coil, but I'm not getting any sort of tach signal or spark. I just got my distributor back from having it rebuilt at Philbin, and now it doesn't seem to be working Before it would work, but the car just wouldn't run. Now I have these fuel pump problems as well I was under the impression the fuel pump should get full voltage if I'm cranking, regardless of the tach signal, though? Quote Link to comment Share on other sites More sharing options...
Cougar Posted February 25, 2008 Share Posted February 25, 2008 The REV sensor will shut down the pump if there isn't any tach pulses. You now need to see if the pickup in the disty is working. Also make sure then is voltage on the minus side of the coil. Quote Link to comment Share on other sites More sharing options...
CornerHard Posted February 27, 2008 Author Share Posted February 27, 2008 It looks like that's what it is - if I turn the ignition to "on", then take the black and yellow harness wires from the ignition coil and tap them together to create a fake RPM signal, my fuel pump and tach start working again. Quote Link to comment Share on other sites More sharing options...
Cougar Posted February 27, 2008 Share Posted February 27, 2008 Good sluthing CornerHard. I wonder what happened to the disty while it was in the shop? Are you sure you got the same unit back? Quote Link to comment Share on other sites More sharing options...
CornerHard Posted February 28, 2008 Author Share Posted February 28, 2008 Thanks for the help, Cougar. I suppose I don't really know if it's the same one or not, since they rebuilt just about everything in it. I'm trying to understand what's going on here, though: The wires coming from the car harness: Black wire (power supply): +12v and almost perfect continuity with ground Yellow wire (tach signal): No voltage or ground The wires coming from the distributor: Black wire (+ terminal): some continuity with ground Yellow wire (- terminal): slightly less continuity with ground The ignition coil fires when there's a change in the current flowing through the two terminals. The distributor either causes flow through the coil periodically or interrupts flow through the coil periodically - I've heard conflicting reports as to which way it works. What I'm wondering is, why is the power supply wire also a ground? It seems like almost all the current is just going to flow through that circuit and not go through the coil at all. Is the power supply wire supposed to be a ground? What changes about the distributor wires as the rotor goes around? Could I wire a straight 12v to the positive terminal or is that where the external resistor is needed? Quote Link to comment Share on other sites More sharing options...
Cougar Posted February 29, 2008 Share Posted February 29, 2008 The coil generates a high voltage when the current running through it is interrupted. The sudden stop of current flow makes the coil's electric field collapse and the high voltage is produced. I think you have a reluctor type circuit in your disty. If it was working before had it worked on then the shop should fix this for you. The replacement parts are expensive. Quote Link to comment Share on other sites More sharing options...
CornerHard Posted February 29, 2008 Author Share Posted February 29, 2008 Yep, the shop warranties their work, so I may end up sending it back. So the yellow wire on the distributor is the one that has its ground interrupted by the reluctor, correct? That would cause the current to stop flowing through the ignition coil. Quote Link to comment Share on other sites More sharing options...
Cougar Posted February 29, 2008 Share Posted February 29, 2008 Yes, I think that is correct. One other thing, in my previous post it may have been more correct to say the magnetic field of the coil collapses instead of electric field. Though the two are related to each other. (Where's OB99W when you need him?) Quote Link to comment Share on other sites More sharing options...
WoodsWagon Posted March 1, 2008 Share Posted March 1, 2008 DId the engine sputter and die, and choke alonge a bit before it stopped, or did it just die? If the timing belt snaps, the disty won't get turned, the rpm signal won't get sent, and the pul pump won't get turned on. My dad was chasing a fuel pump problem , had all the diagrams printied out and laminated, and spent lots of time on it before he gave up on the car. I fixed the broken T-belt, and the fuel pump issue remedied its self. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted March 1, 2008 Share Posted March 1, 2008 I fixed the broken T-belt, and the fuel pump issue remedied its self. That's nice and all, but EA81 land doesn't have timing belts. GD Quote Link to comment Share on other sites More sharing options...
CornerHard Posted March 17, 2008 Author Share Posted March 17, 2008 In my case the fuel pump wasn't working because the distributor wasn't sending an RPM signal. Apparently, the car won't even prime the fuel filter unless there's at least some signal. Once I got the distributor working, everything was good again. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted March 18, 2008 Share Posted March 18, 2008 In my case the fuel pump wasn't working because the distributor wasn't sending an RPM signal. Apparently, the car won't even prime the fuel filter unless there's at least some signal. Once I got the distributor working, everything was good again. It should prime for about 1.5 seconds after key-on regardless of tach signal. Of course that's not long enough to get much fuel flowing to the filter - but the pump should still run. incidentally - what was wrong with the distributor? Was it something the shop did? GD Quote Link to comment Share on other sites More sharing options...
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