More weird emissions stuff

[ringram]

Ok, Ive been helping a guy with a case of a bad install.
Basically a shop installed headers with no o2 bungs, so mounted them post cat.
o2 switchpoints were well into the 500mv range and not surprisingly the vehicle failed emissions.

Ive advised him to relocate the sensors, but in the meantime we tried altering o2 switchpoints a little.
The vehicle now reports lambda 1.026 so a tiny bit lean, HC is now well down limit is 200ppm count is like 14ppm or something.
Problem is CO is well high, but thats werid because its running bang on or slightly lean. So what gives?

Also he thinks there might be a small exhaust leak.

Anyway plan is to try open loop, but preferably to get the O2 bungs in the collectors installed and relocate O2 and fix leak.

Just wondering if anyone had any thoughts on why CO is high but HC and Lambda is good.

[dfe1]

Double check your lambda readings. If a catalytic converter is operating properly, it should be consuming most of the free oxygen in the exhaust system. Typically you'll see very steady rear O2 sensor readings between 600 and 800 millivolts (if the converters are operating properly) and you should see no significant voltage drops under steady state conditions. That isn't an indication of a rich mixture, it's an indication that there isn't much free oxygen-- because it's been consumed in the catalytic process. In any event, if you're using a post catalyst O2 sensor placement for the primary sensors, the data collected by the sensors will be incorrect and that will cause strange readings across the board. It seems as though your problem might be that the actual air/fuel mixture is far enough off that there's enough O2 in the exhaust to oxidize the hydrocarbons, but not enough to convert CO to CO2.

[ringram]

Yep, we have decided to 1. relocate O2 sensors and/or 2. Go open loop.