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, 47 views)

What was the speed and load conditions for this test? I assume your emission test was ASM. What were the numbers?

Duke

Hey Duke,

Haven't talked to you in a while. Hope things are good with you and your family during this crazy time.

The readings I provided above were at idle no load. The corresponding test numbers for the actual emission test are attached here.

Kurt

Attached Files

ASM Test Results.pdf (257.3 KB, 59 views)

So the HC at idle is in the 250 ppm range? I recall that before ASM the HC limit at idle speed was about 100 ppm, so your car would bust the old two-speed test even though it has decent margin on the ASM test.

High HC seems to be the Achilles heel of the M103 engine family.

Your ASM numbers are very similar to what I get with my '88 190E 2.6 five-speed, but only with shorting the R16/1 resistor and plugging the manifold vacuum signal line to the EZL to disable vacuum advance. Otherwise, it might bust the HC limit.

My engine doesn't have EGR or an air pump. I believe yours has both, but the air pump is only energized during warm up and is disabled once the coolant temp reaches 60C and the system goes into closed loop operation.

Duke