Trying to make sense of emission results

[glucklich21]

So I live in a county that doesn't require testing. However our school does testing periodically that's ran by the state. I was curious about what was being emitted since I'm running my stock 318i exhaust with my M50. Turns out it's handling it just fine, but there's two values that are off that I can't make sense of.




Any ideas?

[Bimmeratic]

Trying to make sense of emission results

Judging by the AFR and O2 readings, you are running lean. Surprised you don't have a higher NOx reading. Everything else seems within range. Are you having any drivability issues?


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[328ijunkie]

Nox is 4?! Someone didnt write down that data right. AFR of 16.6 would be lean misfiring like hell.

[Bimmeratic]

If he was having a lean misfire issues, HC would be much higher and would be way out of the range of acceptable. And I'm assuming the 4 on NOx means 400ppm, which would make much more sense and affirm the fact he is running lean. Could either be a fuel or air related issue. But until the OP fills us in on any issues he is having, or lack of, all we can do is speculate.


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[Todd Black 88]

Tail pipe test?

Exhaust leak?

[glucklich21]

Judging by the AFR and O2 readings, you are running lean. Surprised you don't have a higher NOx reading. Everything else seems within range. Are you having any drivability issues?


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Nox is 4?! Someone didnt write down that data right. AFR of 16.6 would be lean misfiring like hell.

It's not misfiring, not all. It does feel slightly down on power, but gas mileage has been great and no check lights.

If he was having a lean misfire issues, HC would be much higher and would be way out of the range of acceptable. And I'm assuming the 4 on NOx means 400ppm, which would make much more sense and affirm the fact he is running lean. Could either be a fuel or air related issue. But until the OP fills us in on any issues he is having, or lack of, all we can do is speculate.

Tail pipe test?

Exhaust leak?

Tailpipe test and I wouldn't be surprised if there was, it's my car's low mileage albeit original, stock exhaust system.

Here's everyone else's results:

[Todd Black 88]

Idle only test?

[Bimmeratic]

Trying to make sense of emission results

Good gas mileage is definitely an effect of running lean. But it sounds like you might have an air leak somewhere. I would use a smoke machine, if you have access to one, and test the engine and exhaust for any leaks


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[glucklich21]

Idle only test?

Yup.

Good gas mileage is definitely an effect of running lean. But it sounds like you might have an air leak somewhere. I would use a smoke machine, if you have access to one, and test the engine and exhaust for any leaks


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I'll do one and see what I come up with.