The Mass Air-Flow sensor is connected directly after the airfilter with large rubber boots on each side (one to the airbox, and the other to the DK inlets). There is one on all models, except the V8 and V12s have two because of the dual manifolds and inlets.
These readings are performed on my 91 750iL using dual digital multimeters. Please note that the right one (multimeter) had a low battery and thus displayed a little lower than the left one. Grounding the meters at the big jumpstart nut on the left shock-housing, the setup looked like this:
To be able to probe the MAFs you can follow this procedure.
Disconnect the MAF-plug to read the pin-numbers located on the plug. These are very small digits and I had a little trouble making sure which was which. But I finally discovered that they are numbered 1 through 6 in a circular pattern, with number 7 (not connected) in the middle of the plug.
Then when you have located the desired numbers you can pull back the rubber boot on the backside of the plugs and locate that pin for easy backprobing while the connector is pluged into the MAF. The engine will not run if the MAFs are unplugged.
The mixture can be adjusted by drilling out the black plastic cap indicated in the picture. Behind it is a screw that controls the mixture by adjusting the voltage to pin #6...
The above picture displays the reading of pin #6 on the MAFs when the engine is heated up and running at idle, and without having engaged any gears on an automatic transmission. This reading varies and increases somewhat with higher RPM, but should settle around this reading after a short amount of time (just tested to around 2000 RPM).
Below you will see the reading for the same pins with just the ignition turned to position 2 and engine not running.
The reading from pin #3 on the MAFs is a constant +5 volts regardless of engine temperature. It was measured constantly while warming up. This voltage is probably used to supply any electronics within the MAFs their constant operating voltage. +B (constant battery voltage) is supplied through pin #2 on the MAFs. And pin #1 (or 5 as I don´t recall) reads out a frequency of about 1.65kHz (varies from around 1.55 to 1.75kHz) when the engine is running, and hot. This could seem to be about twice the engine RPM, but is just a theory of mine.
The wiring to the MAFs consist of 6 wires which I´ve outlined in the below table.
I didn't do any extensive probing, and forgot to make a note of which of pin #1 and 5 that carried the 1.65kHz frequency... The Mixture Voltage was 1.38VDC with ignition on, and engine not running. While running, and hot, the voltage was 2.38-2.40VDC.
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