GM900 2.0 runs with Hall Sensor disconnected
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Thread: GM900 2.0 runs with Hall Sensor disconnected

  1. #1
    Saab Fan InEurope's Avatar
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    GM900 2.0 runs with Hall Sensor disconnected

    Had a CEL for a while, but the car ran just fine. Went to the dealer for something else, and asked them to check the diagnostics. Answer was something to do with the Distributor/Ignition.

    So checked and it seems the plug for the Hall sensor had become detached (broken off from the distributor). Even with the connector completely off, the car runs fine.

    For looking in the manual and in other forums, seems that this should stop the car dead.

    Anyone any idea what is going on with the setup?

    2.0i non-Turbo, 1997

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  3. #2
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    Re: GM900 2.0 runs with Hall Sensor disconnected

    InEurope,

    Long time since I had anything to do with a distributor, and even longer one without points ( looked after a MkII Jag for a while ) so I can only assume that the broken connection was on the earth side of the circuit and so the circuit was completed some other way. Might be worth getting a meter out and checking for continuity.

    Even though it still runs, I'd fix it all the same.

    Paul @ Kippen.

  4. #3
    Saab Fan InEurope's Avatar
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    Re: GM900 2.0 runs with Hall Sensor disconnected

    Hi Paul,
    Yes this is really the last use of distributors. You can't adjust the timing/rotate the dizzy, and no points. It really is just a way of using only one coil and sending the spark to the right plug.

    In this case, to time the spark to be in line with the mechanical rotor arm alignment, the Hall sensor acts as the points and fires the coil secondary winding. Which should mean that the car can't run if this isn't connected.

    However this is not just an earth side issue; the connector cable has 3 wires to provide the voltage to the system, and to detect the change when the magnetic field is cut off. All 3 wires are disconnected but the car runs just fine!


    So clearly my understanding of what this does or at least how it's setup is not right. Or I have a magic dizzy

    But yes, I want to fix it, just not clear what I am fixing

    EDIT: Just found this old thread: http://www.saabscene.com/forum/threads/143250-Ignition-Amplifier
    s
    eems that the purpose of the Hall sensor is not too clear
    Last edited by InEurope; 02-15-2017 at 10:19 AM.

  5. #4
    Saab Fan InEurope's Avatar
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    Re: GM900 2.0 runs with Hall Sensor disconnected

    Just to add some information.
    Reconnected the plug to the distributor. Pulled fuse 17 for 30 mins, still had the CEL. Pulled fuse 17 and 28 for a good while, CEL cleared. Not sure if it was the extra time or the extra fuse that cleared the it.

    Anyway, engine runs with no warning light, so I just need to find a way to stop the plug falling off as a new dizzy is way too much.

    When connected, certainly no dramatic change in running or performance. Maybe it does pull under load a bit better, but not really sure if this is wishful thinking :-)

    So at worst, this is a vestigial setup like an appendix and all it does is cause a nuisance when it goes wrong, or it is a subtle sensor to help with timing setting. Some older Porches have a similar setup (Bosch Motronic), and as far as I can see on the forums the latter possibility is the general opinion.

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