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Bad thermoswitch prevent starting?

Discussion in 'Technical Q&A' started by pnorman, Feb 8, 2004.

  1. pnorman

    pnorman Rookie

    Dec 30, 2003
    47
    Can a bad thermotime switch create a starting problem because it controls the warm up regulator?
     
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  3. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    19,485
    Texas
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    Steve Magnusson
    What year/model/version F? (Your Profile is blank!)

    and

    Do you mean the thermo-time switch or a coolant thermoswitch?

    (However, my guess would be "NO" either way -- IIRC the K-Jet warm-up regulator is an open-loop device not relying on other sensor input, but give more information.)
     
  4. pnorman

    pnorman Rookie

    Dec 30, 2003
    47
    I'm sorry, I meant the thermotime switch. 82 Mondial 2v 308...Patrick
     
  5. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
    19,485
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    IIRC there is no functional association between the the warm-up regulator and the thermo-time switch (which controls how long the cold-start injector opens during cold starter cranking) on a K-Jet system.

    What is your symptom -- no cold start and no hot start even though starter cranks well? You've verified ignition spark?
     
  6. pnorman

    pnorman Rookie

    Dec 30, 2003
    47
    I have spark and fuel. If I don't unplug the cold start injector, my throttle body floods. What give the warm up regulator its signal?
     
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  8. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    19,485
    Texas
    Full Name:
    Steve Magnusson
    The K-Jet warm-up regulator is strictly an open-loop device -- it has an internal +12V heater, and it absorbs heat directly from the engine -- so it doesn't use any external electrical "signals" to actively control its behavior.

    Do an internet search on "K-Jetronic Warm-up regulator" you should get many good references like:

    http://www.320i.com/kjetronic.htm (and it shows three other reference links)

    I'd also recommend that you get the Aird Bosch CIS book, or, if you want more technical (but not as introductory) meat, the Probst Bosch CIS book from Amazon.

    With regard to the cold start injector, if you measure the voltage at the connector, it should go +12V for something like 1~8 seconds only during cold starter cranking -- if it doesn't (like it goes +12V during hot cranking), then you could have a problem with the thermo-time switch.
     

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