I have an 89 iroc z. Had the 305 TBI in it but i am putting a 305 TPI motor in it from a 90-92 camaro. The wiring harness and ECM is also from a 90-92 camaro. BUT...... I read that there will be some wiring alternating required if the year of the body does not match the year of the harness. Is this true? and if so.....what alternations would I have to make?

From tacreationsusa.com

Since TPI uses 8 injectors VS 2 (TBI), it uses a different ECM and harness. It will be easier if you swap a harness from the same year and make vehicle, as it will plug right into the dash with no changes. For example, if you have an 89 TBI Camaro, you would want an 89 TPI Camaro harness. Only the 90-92 TPI harnesses will require a wiring alteration, only 2 wires. If you mismatch years, the harness will require some rewiring.

 

Really, what your doing is converting from maf to speed density. Better read up on that as well. You "will" experience wiring harness incompatibilities. Sorry. Expect it. Basically put, replace the harnesses as needed to be compatible with the computer and your new motor and drivetrain. No telling where that may lead you. Welcome to your journey! Been there, done that and it's a long and winding road. Be patient and do not cut stuff. Hopefully, you have a complete donar vehicle?

Here's a helpful thread; http://www.chevythunder.com

Good luck

PS. I did the same conversion with my 87 IROC. PM me if you'd like more details.