I'm running a MS1 in a 95 turbo car using fab9 cop kit. The issue I'm having is tuner studio reads 13.4 volts when the car produces 14.4 everywhere else, at the battery, alternator, coil driver...... all grounds are good. the car is breaking up at about 4k rpm. Do I need easytherm or something else to correct the voltage difference? thanks in advance

 

Measure the voltage between the ground wire on the MS, and the engine block. Should be 0.00V, or say 0.01V. Do the same between the +12V wire on the MS and the battery, again should show 0.00V or 0.02, something very small. This is measuring the Voltage DROP across each wire.

If the car is 14.4 and the ECU is 13.4, you're missing 1.0V and you'll figure out which wire doing the above, then start narrowing it down till you find the "spot" where all the drop is happening.

Likely it's a bad ground.