No RPM and IAT & Water Temp drop during cranking
 

I have a 92 JDM FD which has the weirdest no start condition.

During cranking the rpm readout on the commander monitor screen stays at zero.
The IAT and Water temp go from valid values (~15degC) to "---".

-PFC tested in other FD and fired right up
-Rywire engine harness
-Known working rpm sensors
-less than 1mm gap between rpm sensors and trigger wheel
-All engine bay grounds redone

Thoughts?