As long as all of the sensors and EEC are healthy, the computer will make sure the mixture is exactly where it needs to be to make the least amount of emissions (and the most power). If any of the sensors were reading any of the monitored engine operations to be out of range, you would get a CHECK ENGINE light. That is exactly what the CHECK ENGINE light alerts you to - any emissions control function not operating properly. It's having a miscalibrated EPROM chip (LPM, Superchip, etc.) that will let you get away with a condition that will fail the emissions test.
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Scott
1991, 252K miles, glass hood, police grill, SVO shifter, Catz fogs,
K&N, 73mm MAF, Superchip, PP Y-pipe, Borla cat-back, 190 lph pump
Eibach/Tokico/polyurethane, SHO Shop front & rear strut braces,
16x7.5" Moda R1, 225/55ZR16 Bridgestone RE730, -1 deg camber x 4,
Class II hitch, Silver award at the SHOklahoma Car Show
[This message has been edited by sdpatt (edited 10-28-2001).]