These are the pins that need to be changed when converting an 1226870 1985 Model TPI ECM to the later 1227165 1986-'89 ECM, special thanks to Mike Davis.

Old C3          NEW P4
('6870)         ('7165)
==================================================================
Repinning
-----------                                   Diagram says Grn/Wht  
A11             C12  -- Manifold air temp   - but memory says Tan
D2              C1   -- Cooling fan control - Green/White
D8              C15  -- EGR diag switch     - Green 
B4              D4   -- EST control         - White
D12             D2   -- Black TPS 5V return - Black
C9              D11  -- Fan Request         - Dark Green
B11             B12  -- MAF Sensor          - Dark Green
D13             A11  -- Multi Sensor Gnd    - Black 

Splicing
-----------
C15 splice to   D16  -- 2,4,6,8 Injector    - Light Green
D14 splice to   D15  -- 2,4,6,8 Injector    - Light Green
     NOTE: Seems like one of these was backwards on my '870 ECM,
            makes no difference though, as all 8 injectors fire at once.

New hookup
------------
                D12 goes to Maf Burnoff relay
Removal (unused)
------------
C12 remove           -- Backup mode TPS     - Dark Blue

NOTE: When using an '89 Calibration, GM changed the A/C pressure switch
      from normally open, to normally closed.  If left unchanged, your
      fans may run all the time.

ALSO: Keep in mind that relays will have to be wired in for the MAF Power
      and burnoff functions.  See diagams on this site.