We dyno my 86 vette today and discovered my Diacom GM PLus was showing a rich condition yet the dyno was showing a slight lean condition from idle to about 3000 rpms. The o2 sensor is a brand new bosh. Is there something I can adjust to get the ECM to reflect what the dyno is seeing?

Frank

Nope, you've just witnessed why there are WB O2s, and then Switching O2s.

A switching O2 just tells you if your rich or lean, that's all it can reliably do.

If you want a O2 sensor to monitor AFR then you need a WB.