so i pulled the motor and harness outta my car today and noticed the tpi harness and the LO3 harness are generally the same, but the LO3 harness has 2 extra pins in the harness. anyone else notice this? are they important wires? ahhhh

 

You really need to be more specific. What year is the car, what year is the harness. Where are the pins located?

 

This link should be the Schematics for the 86-89 TPI ecm

http://chevythunder.com/198689_f__y_body_1227165.htm

This link should be a Schematics of the lo3 ecm

http://chevythunder.com/1228746_ecm_198992_tbi.htm

print them out and compare. You will find that several pins differ from one to the other. I used my lo3 harness for my TPI but a few pins had to be moved. The schematice links are the very ones I used

This is a link to the tpi ecm pinout, it will help but I can't find one for the lo3 so you will have to trace each wire down.

http://chevythunder.com/fuel%20injec...ecm%20#1227165)

You will also have to do some work to the engine end of the harness to make it work. Again, use the links

If I can help let me know,
Dewayne