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,