I am trying to determine the interchangeability of two Lean Burn ECUs. The original ECU on a 1985 Diplomat is part number 4289673. I acquired a Lean Burn ECU with the part number of 4379255. The 2002 Mopar Remanufactured Parts catalog (see attachment) lists ECU 4379255 as fitting 1986-1988 RWD vehicles and notes that it is a "Field Fix". The original 4289673 ECU is shown to fit 1985-1989 RWD vehicles. Since ECU 4379255 is listed as a "Field Fix", I assume that a service bulletin was issued to address a specific drivability problem in the field. Is anyone familiar with a Lean Burn ECU swap for the 1986-1988 Diplomat and Grand Fury? What service bulletin(s) addressed this issue? Thanks!