ECM appears to be defective?

Asked by Jul 03, 2017 at 01:09 PM about the 2004 Mazda RX-8 6-speed

Question type: Maintenance & Repair

The wiring harnesses on the Mazda 2008 RX8s include a shielded 2
conductor branch  for the ESS signal lines. The shielded leads are paired for
conduction of the ESS generated signal to the ECM.  The reasoning for the
shielding and pairing are understood.
Oddly, we have encountered 2 ECMs both of which, when measured, have  
one of the 2 input signal pins shorted to ground. ???
OBSERVATION:
The resulting non-isolated input allows electrical noise to improperly
influence the ignition/injection triggering data. i.e. Hash from the ignition can
sometimes  cause problems at idle. And, arching from the starter brushes,
sometimes will disrupt ignition altogether, preventing engine startup.
QUESTION.
Is this a design/manufacturing flaw, or have we encountered 2 ECMs with
identical defects?
Note:
The 2 ECM inputs from the ESS are 2U and 2X.  The shield connects to 2H.
(See: http://www.rotaryheads.com/PDF/RX8/4EngineControl.pdf)
In our case, we have encountered 2 ECM with pins 2X and 2H shorted
together. We have a work-around but do NOT want to employ it on a
customer vehicle!
Are both of these ECMs defective does MAZDA a reason for tying 2X and
2H together?

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