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Thread: fuel pump runs all the time, even when engine is stopped - mk2 digifant

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    Default fuel pump runs all the time, even when engine is stopped - mk2 digifant

    Hi

    my digi used to do the correct thing, ie on turning the key to "on" the fuel pumps would run for a second or so to pressurise the system and then stop. They'd then run when cranking or when the engine was running. (I understand this is a safety thing such that the pumps would always cut out in an accident where the engine stopped).

    Now (since Sunday) the pumps run from the moment I turn the key to "on", and if I stall the car they're still running.

    From my quick review of the wiring diagrams the signal for the pumps to run comes from the ECU (pin 3) which provides an earth to the fuel pump relay when the engine is running or cranking, and for that short initial buzz to pressurise the system I guess.

    any ideas what has gone wrong? must be an ECU fault I guess. Are those common?

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    it can be caused by a blown ecu, but usually if this happens the injectors are also stuck open and engine floods + car wont run. check in the scuttle tray for a red/yel wire on a 2 pin plug, follow this and make sure its not earthed itself anywhere. disconnect the plug, if pump still runs there is a wiring issue issue between the plug and the fusebox, or the relay is shot
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    thanks John, in the scuttle = under the pastic tray near the ECU and ignition amp module, yes? Is the red/yellow wire you talk about the wire that heads from terminal 3 of the ECU to terminal 85 of the fuel pump relay?

    relay is good, have tested it and replaced it also. No effect.

    see my other post in the 8v section re running problems as I think there may be an issue with the injectors also, I'd assumed a sticky injector but I did check yesterday that the plug for the injectors had 0 volts (and it did) when the pump was running but the engine was not (obviously as I had the injectors unplugged )

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    yeah thats the one, on a ce1 the plugs are on the passenger side where the wiper loom goes thru the bulkhead into the scuttle. the injectors on the CE1 are powered by the ECU relay rather than the fuel pump relay as on CE2, and are earthed by the ecu (hence blown ecu = stuck open injectors)
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    cheers for that.

    Don't suppose you have a wiring diagram handy do you? Haynes is distinctly unhelpful on this problem.

    My car is CE1, which relay is the ECU relay?

    I'm also looking at how the alarm might be impacting on this. Looking at pin 87 of the fuel pump relay I'm getting different resistances dependent on whether the immob is on or off, so I'm guessing one of the immobiliser's "switches" sits between the fuel pump relay and the fuel pump. Pretty sure I couldn't get permanent running of the pump without the ECU signal though as without this there would be no power at pin 87 of the relay anyway.

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    ecu relay is socket 1, its a bog std 53 relay.
    't5a' on the diagram doesnt exist on mk2 digi, you have some spade connectors instead. oh, and ignore injectors to pin N, this is incorrect on mk2 there is a yellow/black wire from a spade connector which feeds them, as i say above its from ecu relay. you'll note there are 2 wires into 1 spade, 1 to the injectors other to the ecu

    Last edited by rubjonny; 27th October 2010 at 11:53.
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    superstar, thanks RJ

    just looking at the fuel pump relay here it is a 6 pin jobbie, mine has only 4 pins! and is a bog standard 30, 85, 86, 87 pinned relay. Could I have been a donkey and just mixed my relays up?? What number should it have on it? (mine is 18.) If this turns out to be it I will do public penance for my stupidity. Per Haynes, which covers CE2 digifant engine management in diagrams 71 and 72, the relay is indeed a bog standard 4 pin jobbie.

    Also on the above, the injectors are still powered by the fuel pump relay, and not the ECU relay

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    18 is the x-relief relay which powers wipers, lights etc. fuel pump relay is 67, 80 or 167. have a look at the fusebox faq stickied at the top of this section

    i never noticed before but the relay in that diagram is also wrong, its showing a k-jet relay rather than a 4 pin digi one!
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    found an 80 relay on the passenger's seat, must have got them mixed up whilst I was troubleshooting the running problems at the weekend.

    I am a muppet

    all works fine now, thanks John

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    Hello my name is John and I'm a dub addict.

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