Failed Emissions NOx - Mercedes-Benz Forum

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post #1 of 7 (permalink) Old 05-07-2007, 09:57 AM Thread Starter
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Failed Emissions NOx

See attached picture... Failed NOx by alot. I was thinkin new cats. The car has not been touched in over 10 years, and I don't want to put a dime into unless it passes emissions. I can get 2 new cats for about $180 and that is my limit on spending. I will do that unless you guys have any other ideas.
1986 560 SEL
250k miles
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1984 Mercedes Benz 300SD Turbo Diesel
1999 Mazda Miata AE, 1989 Tbird Supercoupe
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post #2 of 7 (permalink) Old 05-07-2007, 11:28 AM
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Fix all your vacuum leaks first, injector seals, manifold half donuts, manifold gaskets, clean out the carbon buildup in the EGR system. There are rubber hoses too that need to be replaced.

EGR, check the small short pipe under the air cleaner that connects to the rear cam cover.

It's a big job but worth it.

Check the cat(s) for scrapes or dents indeicating broken elements inside.

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post #3 of 7 (permalink) Old 05-07-2007, 11:30 AM
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Change the oil, spark plugs, and airfilter, and then richen your fuel mixture. Look how much wiggle room you have in HC and CO, but yet you're way high on NOx, so you're apparently running lean.
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post #4 of 7 (permalink) Old 05-07-2007, 02:34 PM
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The cats won't have as much to do with NOx as the EGR and fuel mixture. The hotter the combustion (lean mixture), the more NOx. The EGR takes care of that off idle, and the fuel mixture needs to be 14.7 for best emissions.
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post #5 of 7 (permalink) Old 05-08-2007, 12:56 PM
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EGR is probably your problem. Without CO2 and O2 measurements it's hard to know how the cats are operating but make sure the EGR is working, I'll bet its plugged up.
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post #6 of 7 (permalink) Old 05-08-2007, 01:34 PM
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Also, back off on your timing if you can... I don't know these cars, but that will help, and you're lean--as mentioned before. Also make sure that your car is properly warmed up before the test. Don't turn off your car while waiting in line.

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post #7 of 7 (permalink) Old 05-08-2007, 04:51 PM
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I'll pretty much be repeating what others are saying...

Change out the plugs (Bosch), check your plug wires, cap, rotor, change the oil and filter, check your fuel filter, check/clean the EGR vavle, check for vacuum leaks (seems to be the culprit) and check for any other leaks in the intake system. (around the plugs, EHA, injectors, etc.) New cats could possibly do the trick. But, I don't think you should retard your timing unless you were running high on Hydrocarbons. Your car passed HC pretty good. When I had to get the 190e to pass (from high HC) I retarded the timing to 12 degrees and "created" a vacuum leak to lean out the mixture. If your car uses the R16/1 resistor setup for timing, than you can remove the resistor for 0 degrees timing (runs richer) and run her through emissions again. After checking everything else, of course.

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