If he got an OBD2 P75 it wouldn't even plug in to his harness. As far as your problem, you say you feel like you get detonation...can you hear it detonating, or the car just sputters? Do you have a known good OEM ECU that you can substitute in? The PR4 and P75 ECUs should be the same, as is the P74.
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2015 Ford Mustang GT Fastback - Ingot Silver - 6M - Performance Package - Gibson Catback, JLT CAI, FR 47lb injectors, BAMA E85 tune, Eibach Sportline, BMR wheel hop kit, UPR oil separator, Steeda shifter bushing/bracket
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