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4050 analog tach -- testing crankshaft sensor

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11-28-2009 11:25:32

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deere 4050 with analog tach. prev post said to check for 0.8 volts AC. there are two wires going to and from crankshaft position sensor ( red & blue). when at low idle should one wire show volts coming to the sensor ? which wire red or blue ? should this be DC volts ? other wire (from senor) should show 0.8 volts DC or AC ?

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11-28-2009 14:18:41

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 Re: 4050 analog tach -- testing crankshaft sensor in reply to cob_crusher, 11-28-2009 11:25:32  
sensor read 0.52 vac, then increase rpm giving 0.56, increase giving 0.58. sensor should be aok. does tach end plug have two wires so i can check continuity and vac increase ?

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Lee B

11-29-2009 17:31:16

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 Re: 4050 analog tach -- testing crankshaft sensor in reply to cob_crusher, 11-28-2009 14:18:41  
You have a simple magnet and coil generating the AC pulses in the sensor. It would be normal for the voltage to rise when speed increases.

The other end of the wires must complete the circuit in order for it to work so YES, you can check continutiy at the tach end of the wires provided you have access to them.

With voltages these low, wiring problems occur with the slightest leak of either water or oil into connectors or wires themselves. Even when all connections are clean and sealed, signals can get lost when they start out at .52 volts. One tool to use in this event would be Radio Shack's Contact cleaner, it will clean connections and prevent further contamination if used with current weather proof connections likely to be found in your tach sender circuit.

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11-28-2009 14:31:10

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 Re: 4050 analog tach -- testing crankshaft sensor in reply to cob_crusher, 11-28-2009 14:18:41  
It's frequency/pulses, not voltage that is sending the signal to the tach.

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11-28-2009 11:39:21

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 Re: 4050 analog tach -- testing crankshaft sensor in reply to cob_crusher, 11-28-2009 11:25:32  
Check for AC voltage BETWEEN the two leads from the pickup coil.

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