28' 2001 ZXO Scorpion, port engine runs for 15 mins cruising at 3000RPM and then loses 500RPM, with occasional backfires. Problem gets worse as time progresses, to the point it loses plane. We have swapped ignition modules (in the distributors) and the Ignition coils. Was able to run our DIACOM scanner on the engine and record the event, the only thing that really changes is the MAP sensor voltage increases from 3.53 volts to 3.85 volts as rpms drop... I would think that at a constant throttle position that the number should decrease as RPM's drop but I very well could be wrong. Only other thing I can think of is the pickup coil in the scorpion style distributor, but I am unfamiliar with how to get it off. Does anyone have any thoughts on this? Also something peculiar was that both engines read -40F on the MAT sensors. Also our Fuel pressure gauge indicated 30lbs fuel pressure port motor, but only 23 on the engine that runs well. I will attach screenshots of scanner results before and after power loss.
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