1994 Mercedes c220 California Smog Check II Results

[ericnguyen]

Dear friends:

My 1994 MB c220 has just passed the new California Smog Check II. However, I am worried about its HC emission results, which are pretty close to the maximum allowable limit for HC emission at both 15 mph and 25 mph.

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At 15 mph:

MEAS MAX AVERAGE
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%CO2 15.6 N/A N/A
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%O2 0.0 N/A N/A
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HC(ppm) 74 85 21
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%CO 0.09 0.50 0.06
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NO (ppm) 7 695 150
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At 25 mph:

MEAS MAX AVERAGE
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%CO2 15.6 N/A N/A
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%O2 0.00 N/A N/A
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HC(ppm) 47 50 13
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%CO 0.08 0.47 0.05
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NO (ppm) 2 717 136
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Legend:

MEAS = Measured results on my 1994 c220
MAX = Maximum Allowable Emissions
AVERAGE = Average Emissions for Passing Vehicles
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Here are my comments on the results:

Bad news:

-High HC (ppm) numbers are on the border of maximum allowable HC emission, which may be caused by either incomplete internal engine combustion OR the temperature of catalytic converter is too low to burn off the excess HC in the exhaust gas.


Good news:
- Extremely low CO and NO emissions (nasty gases)
- High %CO2 emission (15.6) = complete combustion OR complete reduction of NOx to NO, with extra oxygen to oxidize CO to CO2.
- %O2 = 0.0 means that either the oxygen sensor = good and/or catalytic converter = good.

My wife took the car to the smog check station, but I did remind her to rev the engine to 2K-3K RPMs several minutes before the smog check began. Unless she did not do what I asked her to do, the high HC numbers seem to indicate that the combustion process is not up to specs. I heard that several generations of MB engines have been rated as "high polluters" (in HC emission?) regardless of their condition, so I would like to ask any other C-class owners to post their smog check results for comparison purposes.

Please post your comments and suggestions!

BTW, I did a new oil change several hundred miles before the smog check.

Best regards,

Eric

[Dana B.]

Dunno Eric, you might want to post this in an MB gasser forum. Diesels don't require smog checks in CA.

[olpos]

eric, hope this sets your mind at ease. as a so. cal smog tech, there have been some changes to the test.
back when the two speed idle test was done ,the car ran the entire test. this gave you your best numbers.
now with the dyno test it is changed.
the test can run a long time if needed. but what happens is when the machine sees your car is passing it stops the 15mph test early, very early in most cases. then it jumps to the 25mph test and does the same thing.the test can run about 4 times longer. i think this is done to save a car from possible overheat or keep the dyno time low for more dyno life. with your co2 and 02 numbers great i think the test assumes your car is passing,then on to the next test.
most cars tested, even 2003 cars have hc numbers only 2 or 3 numbers from failing. this includes hondas with ultra low emision motors which should have numbers that are zero or almost. most new cars i test are at the almost fail on hc's. so anyway the numbers you got are not the best,by far. if you want better numbers ask for a tire dry run before the test.
with dyno test if you shut off the car before testing, it makes no change in 99 percent of the test. the 15mph part of the test will run longer to heat up the cat. seems to work pretty well.
after 1996,obd2 cars , they pass the test even when started stone cold and run for two minuites,
anyway's with your co2 numbers so high, the combo of fuel system and and cat are at thier peak, great numbers, higher than most cars. and your nox numbers are very,very good. with these numbers your car most likely runs at zero or almost zero on hc and co, when on the freeway with cat fully warmed up.
hope this is not too long winded. most cars don't hit 15 percent co2, which yours topped no problem. this is the number that says the most.
fellow mb nut
rich

[ericnguyen]

Dear olpos:

Thank you very much for your "insider" information. You've really made me feel better about my c220

Best regards,

Eric