Porsche ‘air volume’ to ‘air mass’ meter conversion (1999)

 

To achieve faster throttle response and less air resistance we replaced a standard Air Mass Volume sensor like this:

Bosch_Air_Mass_Sensor

in a Porsche 911 (964 3.6L engine) by a newer type Bosch Air Flow sensor (HFC unit) like this:

bosch_mass_air_flow_sensor

Unfortunately the output signals don’t match and at that moment reprogramming the Motronic was not an option. So I decided to make a programmable converter which took the signal from the HFC unit and emitted a signal the Motronic would accept as valid input.

The converter unit was made with a PIC16F84 microcontroller connected to a Philips I2C PCF8591 8 bit AD/DA converter mounted in a sturdy metal box.

IMAG0051 IMAG0052 IMAG0053 IMAG0054 IMAG0055 IMAG0056

With a laptop and some special written software (with Xforms under Linux) the curve for the signal was adjustable by mouse and after some hours of tweaking, CO measuring and testdriving the best settings were found.

Bosch_Mass_Air_Sensor_correction_curve_plotter

 

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