My 1991 300D failed the Colorado diesel exhaust opacity test today. The test doesn't actually test the exhaust for anything bad, it just checks to see how much light can shine through the exhaust. It is a joke, but regardless, my car failed and I cannot renew its registration.

The limits set for my car in the lug down test they perform are 35% at 60, 50, and 40 mpg. My car showed 28%, 36%, and 45% in each respective test.

Where should I start? I need to reduce the amount of visible smoke that my car makes. It does not burn any oil or coolant. All of the smoke is unburnt fuel. The air filter was changed two months ago. The fuel filters are pretty old (probable cause?). The injectors were replaced less than a year ago. I normally run with DFC or 85+, but I have been out for two months.

HELP!!!

Edit: I just had a friend drive the car while I followed and observed in another car. The emissions test seems reasonable, as my car does produce more smoke than it probably should. The smoke is black/grey in color. It is mildly present on idle, heavier on acceleration, and not present when cruising at speeds >45 or when decelerating.

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Ben

The MBs:
1976 300D (W115) - 330K and still going (sort of)
1991 300D 2.5 Turbo - Sold at 221K
1983 280SEL - Sold at 206K
1981 300SD - Sold at 232K