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Old 03-14-2003, 09:57 AM
sbourg sbourg is offline
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Join Date: Jul 2001
Location: SoCal
Posts: 1,303
If you get a varying voltage reading as the rpm varies, this means the resistance is not always infinity. Best is to clip the leads on the unplugged sensor while slowly moving the speed sensor vane (engine off). Across some 2 pins, you should see the resistance vary smoothly across some range. If the reading at any point jumps to infinity (or a much larger value), the sensor is bad. Be careful, though. All meters have a maximum resistance capability, and will read infinity above that. If your meter is not autoranging, this point will occur in each range at a different value. Too, digital meters can be frustrating for this sort of measurement - an analog meter is better for trying to judge smooth pot operation.

You will likely find the pot operation is acceptable for readings off-idle, due to the larger amount of time the wipers spend moving about at idle than at higher load conditions. If you replace the sensor, take as many resistance readings as possible corresponding to different positions of the sensor vane. Also measure the total resistance from 1-3 (where you measured the 4.88V). This information will allow you to mechanically calibrate the new sensor (assuming that is possible, I haven't yet had to do this on ours).


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