mbc280

I have a '94 C280 and it failed AirCare when I took it for the test a few days ago -I'm in Canada, BC. The reason was high emissioning of NOx -everything else like CO or CO2 was fine... Anyhow, frankly I'm not willing to spend hundreds of dollars to fix this and want a rather cheap way -perhaps a trick to fix it temporarily I've heard the problem *might* go away if I take out the air filter for the test (or just replace it with a new one). But I'm not sure...

I'd appreciate any advices.

MARK CUMMINS

Check the EGR Pipe from the valve to the Manifold...It May be restricted with carbon build up...seen several

Hal H

+1 for Mark's comment. The primary function of EGR system is to reduce NOx emissions.

It introduces an inert gas (no oxygen basically) that will lower the combustion temp which in turn reduces the NOx levels. Very common to have carbon build up in either the valve or the ports/tubes which render it non-functional.

In older M-B's this happens a lot if the car is primary driven at low speeds - city driving - short distances.

Longer highway speed driving conditions help burn off carbon build up, but actual driving conditions vary from one driver to the next.

mbc280

Thanks folks. Could it also be the cat converter?

Hal H

Since you have a '94 (OBD-I system) it's unlikely you have the two-cat system that '96 and newer cars have. On the newer cars, the cats deal with NOx differently than the earlier single-cat setups.

I'd check out the EGR system first to eliminate that as a possibility. The cats mainly deal with converting HC byproducts into less harmful pollutants.

mbc280

Thanks alot. If indeed the valves and/or pipes are clogged can I just clean them (like rinse them or something) or do I need to replace them?

Hal H

There are chemicals used for removing carbon build up (these are very strong solvents, so extra care is necessary when using them).

I recall an old article in the The Star that mentioned a tech that would use an old metal speedo cable on an electric drill to route out a carboned up EGR port tube on an MB engine.

The chemical would be used on the EGR valve, providing it was salvagable AND the diaphram on the valve still worked properly.

Which brings me to another item - yours very likely may be vacuum operated and checking the vacuum lines, valves and any solenoids in the EGR circuit are other items to check...you'll need to refer the the workshop manuals on your particular application to see what components exist on your MY '94 C280...

\Hal