84-87 Grand National 1226459 1227148


The 84-87 Grand National was a unique car available in limited production. These vehicles featured sequential injection, distributorless ignition systems and other groundbreaking features. A combination of unusual and off the shelf ECMs/electronic components make for some unique needs.

These vehicles used two ECMs. 84-85 vehicles came equipped with the 1226459 and 86-87 vehicles came equipped with the 1227148.  These ECMs were used in a very select few other V6 vehicles of this generation with different programming for non-turbo applications.  It is possible to swap the 86-87 computers into the earlier vehicles.  Datalogging is improved with the later computers.

The Grand Nationals have a cult following.  There is a lot of information to be found in general on www.gnttype.org and the chips/ECMs are covered especially here.

Hardware Required for Tuning

  • The “early” 84-85 1226459 use the G2 *** 0.6″ *** Chip adapter
  • The “late” 86-87 1227148 use the G2 *** 0.45″ *** Chip adapter
  • To reprogram the ECM, both adapters accept a 28 pin EPROM like the C2 27SF512 chip.
  • WARNING: This is NOT plug and play!  Desoldering factory chip is required and soldering install for G2 adapter.  (view install)  Order the “Install Service” and send us your ECM if you’re not comfortable with soldering work.
  • After a chip adapter is installed, our “standard” OBD1 GM tools can be used:
    • BURN2 chip programmer programs chips
    • ALDU1+CABL1 cable allows laptop to log data with appropriate software
    • Ostrich 2 with SocketBooster allows real time tuning while vehicle is running
    • APU1 / AutoProm programs chips, logs data and allows realtime programming in one unit along with optional wideband logging.
    • TunerPro RT can be used with the $1D (84-85) or $31T /1227148Turbo (86-87) definitions for editing and logging