Failed idle CO, what to look at.

[NM Tom]

Failed idle CO today. Here are the readings

High speed Idle

HC 59 Limit=200 HC 186 Limit=200
CO .76 Limit=1.20 CO 2.04 Limit=1.20
CO2 13.0 CO2 12.1
O2 2.67 O2 2.65

Currently running 60# injectors with Eric's emission chip. Cat installed and it was only used once, last years test when all passed. What should I look at to lower the idle CO level.

 

[Eric Stage I]

High CO typically can mean it's too rich. Get the car running with the emissions chip and see what the BLM is at idle. Make sure the BLM has not hit the high or low limit (90 and 160 in that chip). Also, an exhaust leak before the O2 sensor might throw the mixture off.

Regards,
Eric

 

[NM Tom]

Hey Eric, my BLM's were high. I set the FP at 36# line off, I think thats were I had it last year. My translator setting is set to no change, should I run it at 10% lean?

 

[Eric Stage I]

You could try it, but the BLM will go up to compensate for it. It's feedback from the oxygen sensor that dictates the air/fuel ratio in closed loop. If you lean out the fuel, the BLM will keep going up to get the A/F back to 14.7. It would have to hit the upper BLM limit (160) before it would stop adding fuel.
It sounds like maybe the O2 sensor thinks it lean and is adding fuel. That could come from an exhaust leak, or a bad O2 sensor.

 

[gofstbuick]

CO2 is too high. If a new O2 sensor does not drive the CO2 up and the O2 down, I would suspect a cat. The cat completes combustion, therefore, it should use O2 during the oxidation process. Make sure you don't have an exhaust leak before the cat causing false O2 readings. On good cat, O2 will be 0-0.3 and CO2 will be 14.7 or higher (especially on a two speed idle test).

 

[NM Tom]

Did you mean my O2's were too high? It shows my CO2's being low compared to your example. I took my THDP off and put the stock DP on with the cat and I did find a leak at the elbow\DP joint. I fixed that and I'm going to install a new Denso. The O2 sensor "seemed" to be OK, but it does have quite a bit of race gas that has gone through it. I was close before, maybe these 2 things will get my O2's lower, and my CO2's higher which I assume will bring the CO down at the same time.

 

[gofstbuick]

Perfect combustion(for an internal combustion engine) converts HC and CO (along with ignition, pressure and O2) to energy and yields a byproduct of CO2 and H2O. Consequently, O2 is used up during the combustion process. A catalytic converter uses heat, a catalyst (platinum or plaladuim) and O2 (stored in the substrate) to convert HC and CO to CO2 and H2O. Hence if the catalyst is working properly, exhaust O2 content will be 0.3% or less and CO2 will be very high. From your readings, O2 is 2.67% and 2.65% respectively and CO2 is much less than normal. So either you have an exhaust leak (could come from the EGR valve), a compression issue, an O2 sensor issue, possible fueling problems or your cat is dead. The cat is the last item to look at assuming the engine management is in fuel control. Typical two speed idle emissions (with a cat) should result in zero O2,HC and CO and around 15.3% - 15.6% CO2.

 

[NM Tom]

I sealed up the elbow\DP joint and threw on a new Denso and she blew clean enough for a 2 year pass. Thanks for the help guys.