Duramax smog check

2004LB7

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Dec 15, 2010
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Forgive me if this is posted in the wrong section

so, i did a smog check on my 04 LB7 (california :screwy:) and passed of course. anyways the technician and were discussing some of the differences in emissions between a gas rig and diesel.

we decided to put the sniffer in the tail pipe and run it on the dyno. yeah, i know it is not set up to check diesels but we wanted to see what we would get anyways. this was not an official, connected to the state, etc check. just the test procedures.

here are the readings

HC = 0%
CO = 0.06 %
CO2 = 14.2 %
Oxygen = 17.3%
NO = 1128 PPM

he said if he was to somehow get it to run as a gas truck it would have passed the test per EPA/CARB standards for that year

he was really surprised that the HC reading was so low it read "0", Oxygen was high which is not used in the smog check but interesting, CO was close but still within the limits and NO was well within the limits

to me this looks like a double standard when it comes to emission requirements

nothing too scientific, just some fun at a smog shop where fun rarely happens :driving:
 

2004LB7

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Sorry, yes NO is NOx

The test was maybe three to five minutes on the rollers. Engine was cold too. Didn't even warm up the cat first
 

2004LB7

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I wonder if the machine was incapable of detecting HC from diesel? Maybe the HCs in diesel are primarily locked up in the soot and may have been filtered out by the machine as thay would be too large unlike gas HC which is still a vapor