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Old 08-18-2014, 04:42 PM   #27 (permalink)
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If you want to see how GM did it in a previous generation, the ecm for the 86-87 turbo 3.8V6 Buick Grand Nationals has been completely cracked and decoded. It is OBDI, not II. Go to Turbo Regal Web Site, resources, tech info, ecm and sensors, ecm secrets revealed (this is the disassembly of the code in the rom and the 2K of code in the removable 4k chip). Then get chip secrets revealed and more chip secrets revealed, these are the 2k of data tables in the chip with descriptions and formulas, in spreadsheet form. This ecm used both dfco, and for throttle closing conditions not quite vigorous enough for dfco it also did dfe, decal fuel enleanment, where it cut the fuel 10-15% but didn't turn it off. Anyway, you can see the control parameters in the spreadsheets and the code if you want the real explanation :-). GM tended to reuse code so I imagine other ecms from this time frame were pretty similar in their control strategies. No telling how it evolved later, though.

Two other web sites with lots of gm ecm info is the Welcome to diy_efi/efi332 site and Mark Mansur's site, TunerPro and TunerPro RT - Professional Automobile Tuning Software. Tunerpro is a freenware (basic version) and shareware) full version chip editing program, and he has lots of definition files for various ecms so you can browse for yours and see what data tables are accessible. I've done lots of chipmaking for the buick TR's, starting with a calculator and doing manual hex conversions and editing and then using several freeware packages as they were released, and the free tunerpro is very good. I've never had to deal with obdII so I don't know what its capabilities are there, sorry.
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