I have a 85 Iroc want to upgrade to a faster computer It seems no one likes to work with these early units mine is number 1226870. THANKS FOR ALL REPLYS. MR.KIDD

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This question may get better response in the "DIY-PROM" board but I'll throw my .02 in.
I think the best would be the 1227730 or better known as the 730 ecm for 90 - 92 models, which are speed denesity systems. The chip has the most memory on it, 256K, and the guys on the prom board may have found a way to use EEPROM's.
The 1227165 better known as the 165 ecm is for, I think, 87 - 89 MAF models and has the same baud rate as the 730 ecm.
The 730 ecm is favored on the prom board but some guys are hacking out the MAF tables on the 165 and getting some results but slowly.
In either case you'll need a new wiring harnness and maybe some relays and senors.
I'm still getting into this prom burning so I could be a little off on the years and ecm numbers, sorry.
Ask the guys on the prom board.
Good Luck!