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Discussion Starter · #1 ·
Hello,

I have a 1995 RRC LWB and everything works except for the tach.

The tach works but doesnt register correctly. When the motor is running it registers 1,000 rpm. I have a tach/dwell meter that I use to verify rpm and it shows 725 rpm. When I shut the motor off the tach needle doesnt return to 0 but instead freezes at what ever position its at. When I rev the motor the tach will move very slowly and doesnt register correctly. If I rev to 3,500 the tach will only show 2,250, and takes forever to move.

Any ideas as to what this may be? Where does the tach get its signal from?

Thank you.

I will try to post a video showing what Im seeing.
 

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Discussion Starter · #3 ·
sounds like 2 issues. tach gets read from alternator. you might want to change that belt, and also if the tach sticks or reads incorrectly its also a contact issue in instrument cluster.
Thanks!

The belt is new and didnt change anything.

Im weary about pulling that cluster out of the dash. Is it a difficult job? Im worried about breaking something.

Any advice would be most appreciated.
 

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Just an update.

If you put a voltage meter between ground/earth and the wire at the alternator, you are supposed to read voltage. However the voltage output is between 0(when off) and +/- 3-volts at high engine speed. You need to set your meter so it can read very low voltages. I set mine on 3-volts (as a maximum) reading. When I revved the engine, the needle on my meter behaved just like the tach.
 

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Discussion Starter · #7 ·
Thanks for the replies. I have not had a chance to address this issue.

I will check the alternator using the multimeter method described by Paparrover.

Check back for my findings.
 

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The tach essentially reads alternator RPM and calculates engine RPM based off it. If the alternator gas been replaced and the one they installed has a different size pulley then the engine RPM will not correctly correlate with the alternator RPM and you will have tach error.
 
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