At 04:30 PM 7/2/2014, Harold Teer wrote: >My question concerns the measurement between terminals 2 & 3 --- Bentley >says the value should be a resistance change when the air sensor flap is >moved If you measure resistance from either end of the pot to the wiper, it will vary in seemingly arbitrary fashion when you move the vane. Doing that is easy and enough to tell you that it's basically operating. If you hook the ends up to to ground and plus five volts, though, and measure voltage from ground to the wiper pin, you should see a smooth rise from close to zero to close to five volts. With an oscilloscope or an analog voltmeter with a lively needle you can detect little dropouts as you move the vane slowly. This is because of the special design of the resistor plate (made by Bourne, a USA company that builds fancy resistors) which is fed voltage through laser-trimmed resistors at several points along its length rather than only at the two ends. I think the purpose is to allow trimming the response curve and possibly to make it more resistant to track wear. You don't need to use five volts if the AFM is disconnected. Any voltage from around six down should work fine, with appropriate adjustments in the expected numbers. If the AFM is connected to the system, the five volts is supplied for you by the ECU. Yours, David |
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