for reference:

http://www.w-body.com/showthread.php/43001-Rebuilt-Turbo-Grand-Prix-exhaust-crossover-(x-over)-pipes-300-with-core-return
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C21 is position 21 of the C connector for the ECM itself. assuming you acquire a spare wire/terminal, you would remove the red "hairclip" retainer, remove the little silicone plug that sits in the...

yes. with 8F, it's quite popular to feed a wideband signal to pin C21, which on the 91-up grand prixs was used for the a/c pressure sensor. the TGPs used pressure switches instead, so the A/D channel...