O2 sensor ever replaced?

I can see a vacuum leak increasing combustion temps = higher NOx (nitrogen oxidizes >1200C)but this should actually drop your HC and CO.

I found the following article (posted here via Noel a few months back) of good general interest. It is primarily aimed at solving NOx failures, but it does provide some background info on HC and CO.

One thing I learned during re-reading of the article is CO2 is "oxidized" from CO. Of course if the CO2 readings are high, then there must be more CO present to raise the readings. BTW, our local emissions testing facility doesn't test for CO2, just the Big Three.

Motorage - Real-World Repairs for Real-World� NOx Failures
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Norm Cook Vancouver BC; 1989 745T 204,000KM