Differential Pressure Switch - Who knows how these work | FerrariChat

Differential Pressure Switch - Who knows how these work

Discussion in '308/328' started by Archer911, Jun 23, 2018.

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  1. Archer911

    Archer911 Formula Junior

    Sep 26, 2016
    907
    New England
    Full Name:
    Tim
    I thought this switch would either close or open when vacuum was applied but was wrong.

    What happens is that:
    There is no contact closure without vacuum.
    There is no contact closure under vacuum.

    BUT when under vacuum, just after vacuum is released there is is intermittent contact closure.
    I have tested a brand new switch with the same result.

    I tested for variable resistance and found none. I am perhaps testing the wrong way.

    Anyone know how these devices are supposed to behave. Can't find a damn thing on Google.

    This is Ferrari part number 121748 location 18 Table 9 Air Injection.

    Thanks

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  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    That is the correct operation. During cold-running, if you open the throttle quickly (i.e., the intake vacuum drops quickly), the differential pressure switch closes briefly to briefly close the relay that fires the cold start injector to add a "squirt" of enrichment. It's very similar to how the accelerator pump on a carburetor works.
     
    ME308, maurice70 and StuR like this.
  3. Archer911

    Archer911 Formula Junior

    Sep 26, 2016
    907
    New England
    Full Name:
    Tim
    Thank you very much Steve. This is very good to know.
     

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