Steve Gough wrote: > Dear List, I'm trying to tell if I need a new air flow meter for my > '86 Vanagon. Can anybody enlighten me on how resistance should > changeas the vane moves? My manuals (even Probst) are vague.I have > two AFM's in hand. Both show similar resistance changeswith movement, > but one seems to have some drop-outs. Couldn't locate anything in the > archives. thanks, Steve Steve: The AFM is not a typical potentiometer. It is a rather unique configuration of a resistive track for the sliding contact with other resistors attached at various points. Measuring the resistance from the sliding contact to either the ground or the positive end of the array does not give a reading that increases or decreases continuously in one direction. Complete drop-outs (infinite resistance) are of course a bad sign. Otherwise it is hard to tell anything definite by checking resistance. A more meaningful test is to connect a voltage, perhaps 1.5 V from a D or C cell, to the ends and measure the voltage from the slider to either end, as you slowly move the vane from one extreme to the other. The voltage should vary smoothly between zero and the 1.5 V with no drop-outs. Perhaps you could even simulate engine vibration by tapping on the AFM while testing to see if there are any glitches. Have fun, Larry A. |
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