LJ70 tachometer diagnosis

stgibson Dec 1, 2019

  1. stgibson

    stgibson New Member I am in panama

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    I have an 86 LJ70 with a 2L diesel. The tach is not functioning. I originally thought the culprit was the printed circuit on the dash because it was pretty much toast and only one of my gauges was working. I finally found a circuit board in Italy and replaced it and now all of my gauges work except the tach. I have two tachs so I tried both and neither functioned. I then went to the sender which is located in the injection pump and replaced it with a new OEM sender. Nothing. Tried both tachs. nothing. My question is how does one check the signal from the sender to the tach to see if the signal is coming thru and correct??? I have heard you need an oscilloscope. Is this true or is there another way to test it? I would think that out of 2 tachs, one would work, but just in case does anyone have a working tach for this configuration and for diesel?
    Sorry, can't get a photo to upload. I will try later, but the configuration is the same for all 70 series from 1984-1995 w/diesel.
     
  2. Chris Boorer

    Chris Boorer Member I am in australia

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    Just a thought have you checked the fuses
     
  3. stgibson

    stgibson New Member I am in panama

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    It is powered off the printed circuit board on the instrument panel, so if the fuse was blown none of the instruments would work. No individual fuse for the tach.
     
  4. stgibson

    stgibson New Member I am in panama

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    20191201_143542[1].jpg
    This is the instrument cluster configuration for the LJ70
     
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