Innocent
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| posted on 20/8/16 at 03:25 PM |
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Fuel pump short circuit?
Hi, first post on here since buying my first bike engine car (spire gtr zx12), having a bit of an electrical issue. Shut the engine down with the FIA
kill switch, and wouldnt restart... thats when I noticed that the alternator earth protection switch was open - connector was pulled out. Have so far
confirmed that the ecu relay and ecu fuse were fried, and the fuel pump relay seems to now be stuck closed. Starter circuit is fine but no power to
fuel or ignition. So new relays on order and until they arrive im stuck with doing continuity tests only. All sensors and alternator are checking
out ok, just got the regulator to check.
I noticed that the earth wire from the fuel pump has melted through parts of its insulation. I think maybe the alternator discharged through the pump
as the path of least resistance (although I dont know for sure that the wire wasn't like it before this issue and the wire is still in tact and
working). This continues from the pump connector to a point where the earth joins with a wider guage main loom earth wire. No signs of melting between
pump loom connector and pump. So ive tested continuity in the pump, and pos to neg on the loom connector is fine (i assume this is normal for a pump
if its not switched internally?). But.... I am also getting continuity between pos feed on the connector and the tank (or any point on the
chassis/block, grounds are all good). This is when the pump connector is disconnected from the loom. So I assume that this is a fault? And if so, I
cant think what would be causing it without removing tank and pump, a short that maintains continuity from the + to - connectors wouldn't also
give continuity between + and tank would it?
All help appreciated!
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gremlin1234
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| posted on 20/8/16 at 04:58 PM |
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quote:
a short that maintains continuity from the + to - connectors wouldn't also give continuity between + and tank would it?
All help appreciated!
it probably would, since the pump id likely to be nominally earthed on the tank, as well an an explicit earth.
normally, I would suggest a little percussion maintenance to the pump (hit it with something), but I suspect it is a more serious problem than that.
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twybrow
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| posted on 20/8/16 at 07:22 PM |
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Are the fuel pump and ecu relays clicking on when you turn it on? I have had my fair share of ZX12 wiring woes. I had similar symptoms to you after
having fixed another electrical issue. It then wouldn't start. Turned out that the resistor in the grey wire from the ignition switch to the ecu
had broken. This meant no ecu and therefore no fuel etc.
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Innocent
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| posted on 20/8/16 at 08:33 PM |
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Thanks for replies. No, the relays dont switch. They are definitely blown, so waiting for replacements. There's no grey wire on my ignition, I
guess because its been extended with a different colour wire. Ill open up the loom if the relays turn out to not be the only problem.
Gremlin, so are my thoughts right that continuity between feed to the pump and the tank = dead pump? I could test it once the relays are in, but im
not keen given its surrounded by fuel and something has melted the earth wire...
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gremlin1234
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| posted on 20/8/16 at 09:02 PM |
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I don't know what pump you are using, or how you are testing 'continuity'.
however, if just using a meter with a buzzer, a pump would show continuity correctly, as would a light bulb. measuring its apparent resistance is more
meaningful.
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britishtrident
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| posted on 20/8/16 at 09:59 PM |
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You need to work logically and do voltage drop testing. It looks to me very much like a main earth problem, the fuel pump body is acting as path for
the main ground. Testing continuity or resisstance with a DMM is not a valid test where high currents loads are
involved. To check main grounds you need to measure the voltage drop when the circuit is under working load. For example to check the main
engine ground check the voltage between the engine block and the battery negative post when the engine is being cranked.
You can also do it with a test lamp.
see https://www.youtube.com/watch?v=-fyKizH_oQ8
[Edited on 20/8/16 by britishtrident]
[Edited on 20/8/16 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Innocent
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| posted on 20/8/16 at 10:37 PM |
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Thanks, that makes a lot of sense, will check.
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