Hello,

I recently had my car emissions tested and luckily it passed. I had been using a Gunson Gas Tester but it failed the last time I used it. I set the duty cycle at 40-45% and hoped for the best. After the test I asked the shop owner if I could pay for some time on his machine so I could record so data and find an appropriate setting for the car.

Attached is the data I took which I graphed in Excel. This is prescriptive but I thought it would be an interesting discussion to look at real data instead of general thoughts and opinions about adjusting your CIS.

Note: These are tailpipe reading after the CAT so I didn't expect to see a large deviation.

What I think I learned is that, for my car in it's current running condition:
1. A leaner setting around 55% yielded the best numbers for both %CO and HC PPM.
2. There is a dip in the numbers around the 35% duty cycle range. I'm hypothesizing that this corresponds to a more complete burn and it also correlates to a smooth running engine. It was slightly rougher at the leaner settings.

I hope you find it useful to see this data and maybe it will give you some insight about what is going on when you adjust the mixture on your CIS

Attached Files

CO vs Duty Cycle Readings.pdf (105.2 KB, 97 views)