1989 T/A ECM question...

I've got an '89 T/A that came from the factory with a 5.7 250 TPI engine. Somewhere along the line a 5.0 305 found its way into the car which is what I found under the hood. It had a spun main bearing so I replaced it with a 4 bolt 350 block but kept the 305 heads as they were the H.O. heads and would flow enough for my purposes. This raised the compression ratio to somewhere in the neighborhood of 9.5-10.0:1. The motor has the stock 350 TPI roller cam specifications, timing gears, all new sensors, dumped the AIR system and EGR, is bored .030 over, but is otherwise stock. Dished pistons, standard 350 crank, etc.

My question is this. Are the ECMs different from the 305 to 350 engines in this year or do the MAF sensor and various other sensors compensate for the different motors. I have heard both. The dealer pulled the part number for my year and the ECM I have matches the numbers on both 305 and 350 engines, but there were other numbers as well. I ask because it has trouble starting and the check engine light comes on when I finally do get it started but goes off once the rpms go above 2000 or it warms up. However, it idles at like 1100 once warm and hesitates on throttle response. It is a brand new motor and I need to get some miles on it to loosen all the tightness of that up a little, but if it is running lean due to a wrong ECM, if that is possible, or some other issue is there that can hurt the engine, I want to take care of it so I dont destroy a brand new motor in under 1000 miles.

My next move is to get a scan tool on it to read what codes its throwing, if it starts that is, but thought Id ask some questions before monday when I can get a scan tool.

Alright, I did a little research today and found some interesting things out for any of your 3rd gen. guys who might be interested. It turns out, that the difference between ECMs in these cars were the same between 305 and 350 cars, but the PROMS were different. The injectors on 305s are smaller 19lb vs 22 lbs. on 350s. You can use the 19s on a 350 but you have to have a PROM that knows that...basically, custom programming. In addition, the knock sensors are different from the 305 to 350. Lastly, the ESC module needs to be replaced with the 350 one. Everything else was fairly interchangable...intake, runners, fuel rails, etc.

Hope this helps any of you with those 305 to 350 questions. I have a good print out for anyone seriously looking to do the swap.