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Old 03-26-2010, 02:46 PM   #1 (permalink)
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Looking for suggestions on installing a tach

Hello All,
I just acquired an 82 VW Rabbit diesel truck, 1.6 NA with a 4 speed, it is my intention to see how many MPG i can get this little thing up to. The first mod i want to do is add a tach, but it seems that VW in their infinite wisdom did not offer a tach for the diesel models. (at least the older ones)
I read on line that you can use a tach from a gas unit and a signal from the alternator (they call it the "W" terminal) to operate the tach. Involves rewiring some parts of the circuit board and the addition of a trim pot for "tuning"
While i am sure it works i suspect the accuracy.

Anyone know of an alternate way to get RPM data out of a diesel?

-OR - is my best bet to go with the conversion of the gas tach onto my diesel.
Thank you for taking the time to read this

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Old 03-26-2010, 03:45 PM   #2 (permalink)
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race bicycle tachs use a magnet placed on a spoke and a sensor that detects every pass, perhaps a little magnet on the cam belt gear or whater else turns with the engine like the water pump perhaps, than again the alternator signal, could skip this step.

you might be able to find an electronic kit, that is able to do the math. these educational kits usually come with instructions so you just need to know how to solder basically

you might also be able to find an electronic tach kit, wich will be set up to be calibrated etc (unlike stock tachs with might require some hacking)

just some random thoughts...
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Old 03-26-2010, 05:51 PM   #3 (permalink)
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Thank you - that is a great idea (never thought of a bicycle ) - I have no problem building circuits and have the tools to do so - just got to try thinking outside the box -

as a matter of fact i might be able to use a "standard" auto tach with a magnet and a couple of transistors to condition the signal

Thanks again - might have solved my problem - i will keep you advised

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