Tacho sender

[suzygs1000]

Hi,

I recently spent $600 on my instrument panel 89 GQ Patrol TD42, as the tacho had not worked for a couple of years, and the speedo was starting to play up also.

The tacho still does not work, and the repairer assures me that the tacho is now good.

My question is how do I check if the tacho sender unit is operating or not. I have unplugged the unit at the plug near the injector pump, but there is no output according to my led continuity tester. This tester only registers from 6 to 24 volts.

I believe that the output from this sender may only be .5 volts or so. If this is correct, then my tester will not read this. Is this correct? If so, how can I test the sender unit, as I don't want to keep spending unneccessary money, if my sender unit is not faulty.

thanks Dave.

[NissanGQ4.2]

Hi Dave, although it not mandatory you might want to head over 2 the introduction thread (http://www.nissanpatrol.com.au/forums/forumdisplay.php?2-Introductions) and tell us a little bit about yourself and your rig. You might find more members are willing 2 help out if you have done an intro.

Cheers

Todd

[suzygs1000]

Sorry, Todd, I have now done that....

[Yendor]

To get an accurate reading you will need a scope.

You should be able to get some sort of reading with a multimeter. I'm not sure if it's a square wave or A/C wave, I think it will be A/C.

It doesn't really matter what you are looking for is an increase in voltage reading as the engine revs increase.

Disconnect the sensor and connect your multimeter across the the two wires at the sensor....start the engine and record the reading, then increase the engine revs, voltage should increase with higher engine revs.

I would start with the meter on A/C first, if you get no reading try D/C.

You will also need to check continuity of both wires between the sensor and instrument cluster and also check they aren't shorted to ground.

[suzygs1000]

To get an accurate reading you will need a scope.

You should be able to get some sort of reading with a multimeter. I'm not sure if it's a square wave or A/C wave, I think it will be A/C.

It doesn't really matter what you are looking for is an increase in voltage reading as the engine revs increase.

Disconnect the sensor and connect your multimeter across the the two wires at the sensor....start the engine and record the reading, then increase the engine revs, voltage should increase with higher engine revs.

I would start with the meter on A/C first, if you get no reading try D/C.

You will also need to check continuity of both wires between the sensor and instrument cluster and also check they aren't shorted to ground.


Thanks Yendor, I will try that...

[suzygs1000]

By the way, Yendor,

How is the signal generated by the sender unit if there is no power connected to it, as when I disconnect the plug, and put the meter across the wires, the sender is isolated from any power?

Not really that switched on with electrics....
Dave.

[Yendor]

Hi Dave,

The sensor produces it's own power as the engine rotates, the gauge measures this and shows it as a reading on the tacho.

Cheers Rodney