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748 Fuel Pump / Relay Question...

Discussion in 'Technical Help' started by witchellski, Feb 6, 2017.

  1. Hi Guys,

    Before I dig too much deeper, I thought I'd post a query up around the fuel pump / relay on a '99 748. When I switch on the ignition, flick the kill switch on, the fuel pump relay 'clicks' but the pump doesn't prime.

    I've tried running the pump independently using power direct from the battery and it runs just fine.

    So.... If I've got power going to the relay (assuming it is the left hand side one under the seat when sitting on the bike) then why would the pump not prime? I have checked the wires to the pump (from the relay and the battery) and have complete continuity.

    Any ideas what to do next?

    Thanks.
     
  2. Check the side stand relay it's one of the two small black ones on the left hand side of the battery. I had a similar problem were the pump would only come on sometimes.
     
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  3. I had the fuse holder (the larger of the 2 underseat) melt, it was actually still working but the whole thing including the fuse was a glob of molten plastic, so it's quite possible the fuse has blown.
     
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  4. Just because the relay is clicking it isn't necessarily passing current try swapping with the other relay to rule out dodgy unit..
     
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  5. Worth keeping a spare set under the seat as they can go at any time, only a few pounds each from main dealers and cheaper still elsewhere.
     
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  6. Will do a full trace over the weekend... weirdly, it was pumping and turning over, but not firing before the pump stopped responding. Charged the battery and tried again, but pump still not running.

    Like I said, pump runs when hooked up directly to the battery.

    Swapped both relays over and still the same result. Left hand relay still clicks.

    W
     
  7. Check the one at the battery
     
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  8. Witchellski, the two relays have a switching supply and the switched supply (pump and ecu power supply) , from what you describe the switching voltage that comes via the ignition switch and engine kill (orange/blue wire in the 10 pin connector under the RH seat subframe) is working ok. The switched supply has a permanent 12v feed, this is the red wire in the large three pin connector and it supplies both the pump and ecu via the two relays. The two earths in that big three pin connector provide an earth path for both the fuel pump and the ecu and they are usually connected to the black wire that is attached to the ecu mounting screws. You either have relays that are on their last legs, a break in the constant 12v supply or your earth at the ecu is failing or disconnected. Check for voltage at pin A on the battery side of the three pin plug (red wire) and on the ecu loom check for continuity between either of the two earth pins b and c and the ecu mounting screws. Did the bike have or does it have an alarm?
     
    #8 Denzil the Ducati, Feb 6, 2017
    Last edited: Feb 7, 2017
  9. Thanks Denzil... nice comprehensive diagnosis path! Sounds like a busy weekend for me. The bike used to have an alarm, but I stripped that out about 5 years ago. It was causing all sorts of problems!
     
  10. Witchellski, the former alarm splices are a good place to go if you do not have voltage or have intermittent voltage on that red wire in the three pin plug. It is normal for alarms to be spliced into that circuit as a primary immobilizer with others such as into the blue/orange wire as a sensor/secondary immobilizer. Usual place to make the splice is somewhere on the constant live 12v feed to the fuse box (red wire through fuse 1 IIRC), orange blue one is usually spliced under the rear RH of the fuel tank. The diagnosis above is really quite quick to do.
     
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  11. Well, checked fuses, charged battery, replaced relays under seat (engine management) and cleaned big three pin connector under subframe. Went to crank it over with a battery booster (just to give it some extra beans)... I got a splutter of life, but it didn't catch.

    I've got life back into my pump, but it feels like only intermittent sparking. I think a full clean up of the connectors is my next move.

    One question though... would a dodgy starter solenoid (round one on right hand side of battery) cause an issue with sparking? Starter motor turns over, so it's switching okay, but does it have another function? And would replacing it be a good plan?
     
  12. The solenoid won't affect the spark, it's only function is switching the starter motor.
    Steve
     
  13. Real head scratcher this one... for anyone who is still with me on this, here's what I've tried:

    - new battery
    - new relays under seat (and yellow one beside the battery)
    - cleaned three pin connector under seat (getting constant 12v)
    - cleaned main connector under right side fairing
    - checked fuel pump with 12v (runs no problem)
    - checked connector at CPU and all looks good

    I put on ignition and turn engine over on start switch, which it does without being sluggish and I can see the rev needle twitch. Was priming pump last weekend, but now it isn't. Fuel is low, but no warning light. Weird thing is, I rode the thing in there last year!

    Every other electrical item (lights, brake lights horn etc) are fully functional.

    Is there anything I can do diagnosticly to check before I strip the thing right down and check every wire?

    I guess the main symptoms are, intermittent fuel pump and the fact it simply won't burst into life!

    Any help would be appreciated!

    W
     
  14. Witchellski, I am still with you and there is plenty to have a look at. If you have intermittent fuel pump or ecu supply that can either be a broken wire (probably at an alarm splice) or it is feasibly a bad earth for the ecu or the ecu itself. Did you check continuity from the two earth pins in the 3 pin plug? From the plug to the frame and from the plug to the battery neg terminal?. If you have a test lead with bulb or multimeter you can connect up to known live test points (both permanent or switched) then start wiggling the loom, the light extinguishing/buzzer switching off can show a broken wire. Another way of testing is to use a spare length of wire for example from the battery negative direct to the black pins in the three way connector. Whilst you are in there look for the repaired sections of loom for when the alalrm was removed, those are the first places to look for broken wires
     
  15. Thanks Denzil... this makes sense. I'm no auto electrician (as you might have guessed) but this sounds like a straightforward plan, so I'll check out the continuity and earths. I can remember where the alarm was spliced into the loom (and where I subsequently removed it from). This could indeed be the weak point.

    Will post up results! Hopefully good news!

    W
     
  16. Well, after a morning in the garage with a multimeter and a takeaway coffee, I went through the entire ignition system wiring, checking continuity, earths and voltage.... just pulling connectors apart and cleaning the contacts, I got a result.

    Not entirely sure what was actually to fault, most likely a combination of things, but splitting and cleaning the 10 pin connector (under seat), 3 pin connector (again under seat), cleaning the fuse holders beside the CPU and replacing the relays, it finally burst into life!

    The bike has a full service history and has been garage stored all its life, so it just shows you how 'sensitive' they are.

    Big thanks to all of you for your suggestions... Denzil, you kept me focussed on the back end and Duke you were right to point out the fuses. Thankfully done before the decent weather arrives.

    Thanks again,

    W
     
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  17. Result:thumbsup::clapping:
     
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