Sunday, January 12, 2014

MORE WORK ON FIERO TACHOMETER

Although, Larry Pratt, the original converter of the 1985 Fiero GT was able to get the speedometer to work, he was never able to get tachometer working. I was able to find the tach wire in the C500 connector in the engine bay.


C500 - C3 WHITE WIRE FOR TACH

Although I had the tach working yesterday, it was obvious it was reading high, so I went back through the files I had saved from earlier research and found that the V6 puts out 3 pulses per revolution, and the reluctance ring I was using had 6 tabs. This as an easy fix and I just cut off every other tab so there were only 3 tabs instead of 6 on the ring.


RELUCTANCE RING WITH 3 TABS

Now the tachometer appears to be reading closer to what the actual motor RPMs are but still seems to react a little slower that I feel it should.


FIERO TACH SHOWING RPMS

The tachometer circuit originally had a filter circuit that can be made or purchased from Rodney Dickman.


OEM FIERO TACH FILTER


RODNEY DICKMAN FIERO TACH FILTER


FIERO TACH FILTER SCHEMATIC

It looks like a fairly simple circuit, so I will probably just go to Radio Shack and get the components to build one.

The Synkromotive controller also has an input for a tach and I believe also an out put but I have not found a setting for putting out the 3 pulses per revolution I need for the Fiero tachometer, so will need to contact them to see if I can just use one pulse per revolution from the speed sensor and convert it to 3 inside the controller.

Until next time,

Randy
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