spiderwebfx Posted January 8, 2015 Share Posted January 8, 2015 I'm having trouble with the fuel pump in my S12.Firstly, specs: S14 SR20DES14 WA ECU (Manual) S14 DE fuel pump Some custom wiring. So, the problem: I wired it all up, but the ECU will not control the fuel pump. It will start and run if I hard wire the fuel pump so it's constantly running, but I don't want this as a permanent fixture. I have tried two different manual ECU's, and they're are both the same. Can anyone tell me what I'm doing wrong? It's the only thing I need to sort and then the wiring is all finished proper. Its wired like this: This is the ECU pinout. Thanks, Chris Quote Link to comment Share on other sites More sharing options...
Escorto. Posted January 8, 2015 Share Posted January 8, 2015 Cant figure out your diagram but Ecu supplies a switched negative. could be your prob. Edit had another look. Diagram looks right. Quote Link to comment Share on other sites More sharing options...
spiderwebfx Posted January 8, 2015 Author Share Posted January 8, 2015 Cheers, sorry, the diagram isn't very good. I'm not an electrician. The two top lines are +12 constant in. The bottom right is to the fuel pump. The bottom left is the ECU's switchable ground. I believe the switchable ground is where the fault is. Is it possible there is an ungrounded black wire, or do I have two faulty ECU's? Quote Link to comment Share on other sites More sharing options...
spiderwebfx Posted January 8, 2015 Author Share Posted January 8, 2015 I have checked all of the grounds on the ECU and everything is grounded. Unfortunately, I think that means I just have two faulty ECU's. Quote Link to comment Share on other sites More sharing options...
kyteler Posted January 8, 2015 Share Posted January 8, 2015 Didn't you try an auto ECU and it worked or did I imagine that? Quote Link to comment Share on other sites More sharing options...
spiderwebfx Posted January 8, 2015 Author Share Posted January 8, 2015 The fuel pump did yes, but it won't start, or stay running. Most of the automatic related stuff (I've sinced discovered) has been removed from the loom. Quote Link to comment Share on other sites More sharing options...
kyteler Posted January 8, 2015 Share Posted January 8, 2015 Right, so part of the neutral switch might be problematic for both the auto ecu not starting as well as the manual ecu not engaging. If the loom has been butchered you may well need to pull it to bits. Quote Link to comment Share on other sites More sharing options...
spiderwebfx Posted January 8, 2015 Author Share Posted January 8, 2015 Would that prevent the ECU from being able to keep the engine running if I hard wire the fuel pump? Or does that just stop the fuel pump running. Quote Link to comment Share on other sites More sharing options...
kyteler Posted January 8, 2015 Share Posted January 8, 2015 The neutral switch signal not being correct would stop the Auto ECU from letting you start the car. It should still engage the pump on your manual ECU's the same as it does for the auto ECU (I would have thought) but if someone has been butchering the loom then that's likely where the problem is as opposed to two fried ECUs as that just seems unlikely (though not impossible) Quote Link to comment Share on other sites More sharing options...
kyteler Posted January 8, 2015 Share Posted January 8, 2015 Found this on Driftworks: http://www.driftworks.com/forum/technical/77974-sx-s14-auto-manual-ecu.html Sounds like what you're experiencing. No easy solution there but same problems where the Auto ECU is gravy (to a point) but the manual is not. Try bypassing the nuetral switch and using the Auto ECU to run the car up/check if everything works. Quote Link to comment Share on other sites More sharing options...
downtrail Posted January 8, 2015 Share Posted January 8, 2015 Theres a few things that could be wrong. One is a missing ground to ecu some are for injector drives some are for sensors some are for power supply etc. Double check this. The next is 2 speed fuel pump control if the resistor is missing it wont run unless motor is above a certin load point. Short out resistor to by pass as they start and run on lower voltages untill a certin load point is passed ( im not sure if yours is like this but alot are) the inhibitor normally only prevents the starter excitor from energizing but worth a look as im not 100% on that Quote Link to comment Share on other sites More sharing options...
spiderwebfx Posted January 8, 2015 Author Share Posted January 8, 2015 Theres a few things that could be wrong. One is a missing ground to ecu some are for injector drives some are for sensors some are for power supply etc. Double check this. The next is 2 speed fuel pump control if the resistor is missing it wont run unless motor is above a certin load point. Short out resistor to by pass as they start and run on lower voltages untill a certin load point is passed ( im not sure if yours is like this but alot are) the inhibitor normally only prevents the starter excitor from energizing but worth a look as im not 100% on that Fuel pump wiring has been completely replaced. All new wires, relay and fuse so there are no resistors in the circuit. As far as I can tell, all the grounds are grounded, this was checked with a test light. In this car the starter is controlled directly off the ignition I think. It will crank regardless of ECU, even if it's not plugged in, and once it's started, it doesn't die. I'm looking into the neutral switch on it now, although the wire color doesn't match the diagram so I'm not sure whats going on there. Quote Link to comment Share on other sites More sharing options...
spiderwebfx Posted January 8, 2015 Author Share Posted January 8, 2015 Following on from the neutral switch. The wire colors don't match my loom. But one thing I found strange.On the manual ECU, pin 35 G/O is an output to ground via the neutral switch.On the auto ECU, pin 35 G/O is an input to the ECU from the neutral switch.On my one, the ignition input is split off to this pin 35 giving it a constant signal when the car is on.Could this be why the auto ECU works, but the manual doesn't? Is it possible that on the manual, the fuel pump relay is earthed through the neutral position switch on start up? It seems unlikely, but I don't know. Or am I exploring the wrong area altogether? Quote Link to comment Share on other sites More sharing options...
downtrail Posted January 8, 2015 Share Posted January 8, 2015 Check grounds with meter set to ohms even a large resistance will set your test light off but may not be good enough to trigger relay. Disconnect relay coil and test from fuel pump trigger to ground with meter set to ohms to check turn ign on should show dead short during priming then go open circuit Quote Link to comment Share on other sites More sharing options...
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