Well, have stock 305 TPI sys. With new 350 motor. My question is I bought a 89 350 PROM. Some say it wont fit into current ECM. Want to replace ECM. To 86-89 sys. Well, I read the tech. article on this site. Sounds very confusing. I'm not to good with wiring. Will it be better to get new ECM and new wiring harness and just do a swap? Has anyone here done this before? What is all involved? How hard will it be to do?

You're gonna need to get an ECM out of a bones yard for an 86-89 350ci TPI setup. Then you're gonna need a new wiring harness. I would use a new one as opposed to one out of the bones yard because heat, over time, can deteriorate the wire insulation. Check out www.painlessperformance.com They will hook you up with everything you need. Remember... the 86-89 TPI is dependent on MAF not speed density. If your new setup is speed density you may have to get an ECM from a 90-92 and the appropriate wiring harness. Don't take my word for gosple though, all of my experience is with TBI, I'm just going on what I know from my friends.

What do you currently have? If it is a 1985 TPI or a TBI ECM (or SD as mentioned above), then YES, it won't work.

The 1986-89 '7165 ECM can be found in late 80s 2.8 V6 Cavaliers...but double check as some years used a different ECM, but generally they work. Junk yards tend to charge more money if the ECM came out of a Firebird/Camaro/Corvette rather than a Cavalier.

Have 305 TPI in it. With the ECM that was for the 85 Z28. Just trying to find a safe and easy way to convert so my new 350 can run right. Any more suggestions out there? I think the stock number ECM is 1226870?

Look in the tech articles on this website. There's a link to a site that has step by step instructions for converting from the 85 to 86 style ECM. You don't need a new harness, just need to modify the current harness.