failed NOx miserable.....2784, when the max allowed it 1277....bought the car last year...doing tune up soon...always had bad gas mileage...like 200 to the tank about...black smoke at high rpms...tune up should be done this friday...thinking about cat and egr although no error codes or ccheck engine light, and exhaust does not smell like sulfer...smells a little rich i think though...just want your guys opinions...thanks

 

im am having the same NOx problem. I have a larger exhaust so my EGR valve is not opening due to low backpressure. you might want to make sure your EGR valve is functioning, lowering NOx is its main purpose. Also i found out that my air diverter valve (connects to smog pump) is constantly sending fresh air to my header AIR tubes (only suppose to do this in warm up mode, not when the car is in closed loop or heated up), the o2 sensor is picking up this extra o2 and dumping more fuel into the engine, making it run rich. You might have a similar problem. And lastly, check your catalytic converter.

 

vjo, have you tried replacing the egr valve to see if it works new?

 

yeah, i put a new one on there and it didnt seem to do anything. The mechanic that was working on my car gave me a non backpressure valve to test but i dought that it will work. He is also going to try to find a negative backpressure one or test another positive backpressure.

 

hmmm, keep us updated on the results of the tests. I'm pretty interested in this myself.