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Discussion Starter · #1 ·
When I was doing my compression test I just pulled the main spakr wire off the coil.

Noticed a few times that coil had enough jam to Jump a spark across a 1.5" gap to the fender.

After I did comp test, got the air box mouse house cleaned out, I restarted it.

Noticed at idle the Tach is now showing 3500 rpm...

Did the coil sending 20K+ volts randomly to ground kill the Tach signal?

Still runs absolutely fine.
 

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Year/Model/Engine?
The tach signal comes from the engine controller to the cluster, through the tach drive module to the tach.
It is possible that you spiked the tach or the tach drive module, I have seen this before and sometimes it corrects itself.
1)Check to see if you have the correct voltage at the appropriate cavity of the cluster connectors.
a)Voltage should read 2 volts AC.

Next time you are removing a coil/plug wire and cranking the engine use one of these to prevent what happened here from happening again..
 
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