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Air Flow switch for fuel pump control
Posted: Tue Jan 29, 2008 6:03 pm
by cmonref
I have not seen any discussion of the use of an airflow switch in the intake air stream for disabling the fuel pump if the engine is not running. CIS K-Jetronic systems use this method. What would be a source for such an airflow switch?
Posted: Tue Jan 29, 2008 11:15 pm
by john.p.clegg
Why?,when the Ms switches off the fuel pump when the engine is not running already?
John
Posted: Wed Jan 30, 2008 8:04 am
by cmonref
Good question -- as I think I understand it, MS provides a ground for the fuel pump relay control for normal operation, then UN-grounds it when MS gets no tach signal.
For a CIS-equipped 911, the existing fuel pump circuitry can be reused in its entirety. The existing airflow sensor switch's wiring can be connected to the MS fuel pump signal. Or, an airflow sensor can be installed in the MS setup and connected to that same existing wiring to provide a pump shutoff that is independent of MS. That is the method I am exploring. And yup, an airflow sensor/switch is one more mechanical device that can fail ...