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  #1  
Old 10-20-2015, 10:29 AM
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Speedometer an Tachometer reading incorrectly

I've had this problem since i bought it (used). The speedometer reads around 10mph lower than what I'm actually going and the Tachometer is reading about 500 rpm lower than the engine is running.

As far as the speedometer is concerned there seems to be nothing wrong with the speed sensor and my wheels/tires are stock.

The tachometer problem is the same kind of thing, Sitting at idle i can tell it's running normal but the gauge is saying 300rpm.

Anyone know where/what I should check to find theproblem?

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Old 10-20-2015, 11:51 AM
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Re: Speedometer an Tachometer reading incorrectly

Both speedo and tacho signal come from the PCM via the PCI data bus. So it could be that the PCM is sending a wrong signal, or the instrument cluster electronics is misreading the signal. Not sure if the instrument test will reveil anything, but its worth a try:
With ignition in off, push the odometer reset knob and while holding it, switch ignition in run. Now the self test will start, all indicator lights come on, but also the instruments should go to full scale and than back to normal indication. Odometer will count 0000000, 111111111, 2222222222 etc.
Do the speedo and tacho go to full scale and return to 0 during this test? (As soon as the test starts, you can release the odometer reset knob).
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Old 10-20-2015, 12:21 PM
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Re: Speedometer an Tachometer reading incorrectly

Quote:
Originally Posted by Frango100 View Post
Do the speedo and tacho go to full scale and return to 0 during this test? (As soon as the test starts, you can release the odometer reset knob).
Just did the test. They don't go all the way. Both gauges stop short during the test.
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Old 10-20-2015, 09:44 PM
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Re: Speedometer an Tachometer reading incorrectly

So than it seems to be a problem with the instrument cluster itself. Maybe a specialized repair shop can do adjustments on the cluster.
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Old 10-20-2015, 11:14 PM
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Re: Speedometer an Tachometer reading incorrectly

Alright. I'll probably just pick up a replacement. They seem to be readily available at fairly low price. When I do I'll post back here with the results (probably be a few weeks to a month). Thanks for the help in diagnosing that.
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Old 12-03-2015, 08:49 AM
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Re: Speedometer an Tachometer reading incorrectly

I said I would post results so here goes. It was indeed the instrument cluster. replaced with a used one and It works fine now.
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Old 12-03-2015, 07:22 PM
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Re: Speedometer an Tachometer reading incorrectly

Good to hear, happy jeeping.
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