i have '89 350 tpi and its in a '86 trans-am i sold my origall harness with the old motor and i found a '85 trans-am tpi harness at the jukyard I'm having trouble with the ecm the '89 350 tpi came with the reason is vats now i could splice wires to make it work with the vats on other modules needed to run the engine but my friend has a parts car a '91 trans-am that originally came tpi but i know it was for speed density could it ne possible to use the harness of the '91 on my '89 ecm and follow the wire of the speed density and remove it and put in its place the maf wire or wires on the harness

 

Have to do reverse of this. Lots of work

http://www.s10wildside.com/wildside/ecmandtuning.htm

Easier to get a SD '730 computer to go with the 91 harness and run SD.
Many upgrade from MAF to SD because it involves less wiring ; no burn off relays , MAF sensor or spark control module
The 89 engine won't know any different ,