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Discussion Starter #1 (Edited)
Bought a gauge cluster from a member here, is there a difference between the 6 cyl
El camino tach and the one for the v8 ,the reason iam asking is my tach is showing way more rmps than the Rpm calculator shows for my set up ? Yes i have a v8 and not a six. I know they dont interchange,thought some one might know a trick ?
 

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you are sending two extra pulses per revolution so yes the 6 cyl tach will read high when hooked to a v8.
I have no idea how to re-calibrate.
 

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Discussion Starter #3
I know its not correct,just looking for a solution short of going after market.:beer:
 

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Originally Posted by Sandslot;
Is there a way to change the setting to make it work?

Yes.

A tach lets you know the RPM VIA counting pulses from the ignition system.

An 8 cylinder engine produces 4 pulses per revolution.

A 6 cylinder engine produces 3 pulses per revolution.

A 4 cylinder engine produces 2 pulses per revolution.

Your problem can be remedied in the circuit inside the dash that moves the pointer.

It’s contained on a small plug-in PCB or integrated in the main board.

On the PCB you’ll see a resistor chip.

Desolder pins 4 & 10.

Use a 500K potentiometer.

Solder it across traces 4 & 10.

Move the potentiometer to half way.

Start the engine and compare the tach reading with a test equipment quality tach.

Dial it in, unsolder one side of the potentiometer, measure it and buy the matching resistor.

Copied from here:

http://www.thirdgen.org/techboard/electronics/550863-v6-tach-v8-tach.html

More links on the subject:

http://www.s-series.org/htm/how2/recalibr.htm
 

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Sounds a lot easier to buy an aftermarket tach the same size, take it apart and mount it in the dash.
 

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Discussion Starter #6
Wow,i had no idea ! i have been schooled !! thinkk i will wait for the seller to maybe send me the correct v8 tach ,or just go with autometer :beer::texas:
 

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LOL I'm currently working on the similiar thing. While I am taking the time to go the repair route. Since I am the proud new owner of a fluke 123 silly scope and an 87 I wanted to take my crack at the repair. my tach maxes out on power on and nothing else happens. upon further inspection the resister chip spoken of earlier at pins 4 and 10 were burnt. so took the time to go to radio shack to get 2 100k pcb pots and soldered them in series. I get a max of 201k on them and as low as 31k so nice range! I built a signal generator with a 555 timer *got a bad board found out my traces came ungled and broke it was an old spare board.* it goes from 40hz to 580hz you only need 300hz maybe I'll make a calibrator so


at 100 hz you should read 1500 rpms on a V8
at 300 hz you should read 4500 rpms on a V8

so 100hz / 4 pulses = 25rps * 60 seconds = 1500RPM

Now That I think about it that would be an awesome kit to keep your factory tach and have it calibrated.

I need a new board but i am going to try again next week i'll keep you informed if you want. :)
 

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oh and on another noteI plan on leaving my pots in the board for future calibrations bt will be "glueing" them in place.
 
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