Failed E-TEST => High NOx ~ Any Solutions?

[quantass]

I own a 1991 Mercedes 190E 2.3. The vehicle has just FAILED the Emission Test here in Ontario. According to the report it passed every metric but failed only on the "NO ppm" (limit: 700, reading: 1178).

The Ontario Drive Clean pamphlet states for "High NOx on Driving Test" the possible causes:

* Inoperative/ineffective exhaust gas recirculation (EGR) system
* Excessively lean air/fuel ratio
* Malfunctioning or missing catalytic converter (3-way catalyst only)
* Excessive spark advance
* Faulty Thermostatic Air Cleaner system
* Engine deposits or mechanical defect
* Faulty cooling system

A little insight into my vehicle's current condition:

* When i cold start or even warm start for the most part the car will ride rough to idle then shut-off after a few seconds. Turning it back on and giving it gas makes it eventually hold idle ok.

* The rear muffler is in rough shape though I've patched it with some foil and muffler cement

* The catalytic converter is fairly rusty but doesnt appear to have any holes though the piping entering into it had a couple tiny fractures which i used foil and cement to plaster over.

* When driving the car and waiting at a light it runs fine and mostly doesnt threaten to shut off.

* Last year i replaced all the spark plugs and distributor cap/rotor.

* The fuel filter possibly has never been changed on the vehicle since its purchase back in 1993?

* We consistently drive the vehicle with a very low gas tank and have ONLY ever used Regular Unleaded.

* I went to a mechanic before the E-Test to do an oil change and he said from the sound of the car and such he would guess the EGR Valve could be an issue but he was also a bit concerned about the small fractures just before the cat converter.


What is the most cost-effective way for me to approach getting my vehicle up to standards to pass the E-Test "High NOx"? Can i simply CHECK / CLEAN my EGR Valve and perform some in-house NOx test to confirm?

Is the $150 Canadian Tires diagnosis worth looking into to determine the exact issue(s)?

[quantass]

WRT the EGR Valve, there appears to be one vacuum hose coming from the side and 2 nuts near the base. There is also some large piping that attaches / screws into it near the base. I'm going to try removing the EGR by first removing the single tiny hose then unscrewing the nuts and hopefully the whole thing slides out. I will then proceed to clean the innards with some solution and reinstall? Can the gasket be re-used?

[quantass]

Would you guys recommend the EGR clean or should i just skip it and go into Mercedes for a complete diagnosis?

[Blago]

How did they test your car, did they idle it for a while before they tested it? Did they have a fan blowing in front of the car during the whole test? Did you watch them as they were testing it? What were your CO and HC readings?

I bet the car was very hot when they did test. Test the car again, as it is, but with a cold engine, and I bet you it will pass NOx. I once personally tested an older vehicle, in a hot summer day, which failed NOx with a reading of more than 2000 ppm. Let it sit for one hour, did the test again, and it passed no problem.