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

I don't really know anything about your model of car (electronic engine controls?) Sounds like what you need to do to pass is reduce the fueling somehow... adjusting the ALDA on older cars. I would think some kind of cetane boosting fuel system cleaner would help too. Was the car warmed up good for the test? If it was cold it will smoke a lot more than when it's warmed up good on that test.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k

Run Diesel Purge,,,,,get the car hot and go on a sunny day.

What a cumquat of an emissions test.....treehuggers

The car shouldn't respond any differently after running diesel purge. Diesel purge cleans the fuel system, particularly the injectors. Since the injectors are new, I doubt they are the problem.

I myself am a tree hugger, which is actually why I think this is the most asinine test possible. The test doesn't care how toxic my exhaust is, just how visible it is. Any smart enviro-conscious person out there knows that the visible crap is diesel exhaust is just harmless soot that settles to the earth anyways. My car is much better for our air quality than many gas burners out there.

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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

Any diesel in good repair should pass this test. Make sure there are no excessive restrictions in the intake system, air filter still clean, etc. Check your boost system. Low boost could cause an overfuel condition. If your model has an ALDA as a last resort you could disconnect/plug the line to it. That way no extra fuel with boost and it should run really clean! Hook it back up after the test. Sounds like you have another issue though, you should have no problem at all. Put a tankful of biodiesel in it and go get it tested. I bet it passes. RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

There are a lot of possibilities on a car with 200Kmi+. Injection pumps DO get out of calibration over time. Timing chains stretch and timing changes. Dirty fuel can clog injectors (even if new), dirty filters can restrict flow.

In 1991 I don't think there was electronically controlled boost. You may be able to squeak thru your test by pulling the boost sense line off the intake manifold. Your pump will not increase fuel so power will be cut considerably, for the sake of the emissions test, it may work. That is not a vacuum/emissions line, so you are not changing your emissions - though disconnecting your EGR may help out - its very illegal.

Please let us know what you end up doing and how it works!

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Brian Toscano

Where did you have the test done? I had my 85 300td tested at a diesel shop just of west Hampden between Federal and Sheridan (I believe). I can get you their number if you want. They seemed very competent and capable of repairing the vehicle to get it to pass. Stu Ritter on south Inca also could be of help.
I too would be inclined to plumb in a large container of diesel purge and run the car on that while taking the test. I'm pretty sure it would run cleaner on that than on #2 and I've never heard any requirements about what the vehicle must be burning when it is tested.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

There are some good suggestions in here, which I will at least second:

1) Get the freshest, best diesel you can. And put in the highest recommended dosage of additive, either Power Service or Red-Line.

2) Run the car on the highway before the test, and if possible do a few high-throttle accelerations. This helps clean the soot out of the exhaust system.

3) Pull off the boost sense line from the intake manifold. It looks like a rubber vacuum line and heads directly over to the driver's side fender. Probably should cap the fitting on the intake manifold.

4) Some kind of blockage of the EGR valve vacuum line would help. Perhaps a BB or a plastic line coupler that has been epoxied shut.

5) Is it really, really, REALLY cold like it is here? Like 10 degrees? Maybe you should thin the tank of diesel out with about five gallons of kerosene. It's getting tough to find road-taxed kerosene here that hasn't been dyed.

This may pull you through.

Other things that can have an impact could be timing chain stretch or compression on the low end.

If this doesn't work, please keep me in mind for wanting to buy the car. We live free in most of Virginia (no emissions testing).



Ken300D

Don't forget to check the air filter.... a new one wouldn't hurt.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k

mine failed the CT test(also an opacity test) changed filters,air,fuel, -changed oil- and also adjusted valves. passed on the re-test with flying colors.

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

Don't forget about checking the IP timing!

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87' 300sdl

Running just 20% biodiesel should reduce particulate and thus opacity by at least 50%. KEEP U.S. Farming

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87 300SDL 220K
85 300SD 218K
82 diesel Chevette 440K
85 subaru 4WD turbo
83 4.1L buick powered cutlass THE TOY

Ben300SD,

Try a search on the subject. I recall someone on the forum reported the same problem a few months ago, and they ended up cleaning up the emissions by fixing or bypassing the EGR circuit and cleaning out the intake manifold. I may be recalling things incorrectly but the subject is not new.

If you are a "tree-hugger" then just disabling the EGR system, which will increase some of the harmful emissions (NOx I believe), and passing the visual emissions test will not be a satisfying fix. A correctly running Diesel should not fail the test, and fixing the root cause will allow you to continue driving a car that makes a lesser detrimental effect on the environment than the gas powered cars with "invisible" exhaust.

The most likely causes are a malfunctioning EGR or an out of time injection pump. Someone has already posted the relationship between chain stretching retarding injection timing causing smoking at idle and low rpm that improves with rpm increases. So, I would give those options a try first. Good luck, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Speaking on a slight tangent here of biodiesel and "green" fuels:

Know anything about methane injection for a diesel car? Would this be something like propane injection but not as potentially damaging?

We got lots of methane around here..........



Ken300D

Ben:

At that milage, I'd suspect late injection timing. This would also account for the higher reading at 60 mph, since late timing has more effect at higher engine speed.

Check the chain stretch, and if more than 4 degrees, roll a new one in. This will correct both the late injection timing and the late valve timing, and will clean up the exhaust.

If the chain is OK, get the timing re-set properly, it is most likely late.

I had a serious smoke problem with the Volvo due to a sticking EGR valve. Check to make sure the EGR is closing properly -- it must close at high RPM to avoid quenching the flame at high fuel delivery rates. You can simply apply vac directly to the valve and then release -- it must pop closed at once. Mine would stick open after full opening, and would hang for a variable amount of time. However, I wouldn't stand a chance of passing an opacity test -- the smoke was dense, large, and BLACK!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!