Hello,

what a sad day ! I took my 1991 190E 2.6 to the state inspection today for the first time I own it and failed the emission test.

It failed for HC and NOx:

HC ppm 189 Hi-speed (should <120) 188 lo-speed (should <124)
NOx 1685 Hi speed (should <848), 1894 lo-speed (should <937)
CO % 0.42 / 0.43
CO2 % 14.3 / 14.3
O2% 0.6 / 0.6
Dilution % 14.7 / 14.7

One mistake I already realized was that I had low octane fuel in the tank.

Any recommendation what I need to look for ? Is the catalytic converter damaged ? Is the engine burning oil or coolant water ?

Any help is welcome !

Thanks !

Only you would know if its burning oil or coolant....Are you topping up either?

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

No, not for the last 3000 miles.

I checked the car a bit and found the following:

- charcoal container is not connected any more (tube seems to be cut and draws vacuum under certain circumstances).

- Oxygen sensor signal looks ok, alternating between 0.2 and 0.7V, though there is a slow response to load changes. Alternating frequency about 1...2s at 1500rpm.

- EGR valve vacuum present.


I guess the HC value can brought below the limit by an oil change.

But I am worried about the NOX content. It looks like it is twice the max. I will check the EGR for clogging, but if that does not help I am clueless.

Any more ideas ?

With everything being high I suspect the catalytic converter; it may have even been gutted by someone previously. CO is normal for pre-converter exhaust and your O2 is switching normally. If the EGR is operating normally I would just get the converter replaced then retest the vehicle. Should ideally have no O2 in the exhaust; it should be burnt (oxidized) in the catalytic converter as it combines with the CO to form CO2.

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Erich Loepke
2010 Ford Focus
Currently Benz-less

Thanks for the feedback. I passed the test in the meantime. This is what I did:

- disconnecting A/C vacuum hose to the cockpit since there seems to be a vacuum leak there.
- found an other vacuum leak in the charcoal canister line.
- Disconnected smog pump so that no air is feed into exhaust system (not sure if the system leaked air).
- cleaned ignition rotor/distributor
- changed "R16" resistor to a lower value to retard ignition timing
- changed oil
- put 2 bottles of ISO heat into almost empty fuel tank
- drove the car for 30 min on the interstate in 3rd gear prior to inspection

NOx is right on the limit at high speed, and about 10% below limit on low speed.