I would like to know what are the normal Nox levels for a D16Y7 engine on the California smog check. If I know what is normal then I'll know whether or not I should be looking for a problem. This engine does not have an EGR system.

For example, my '96 DX w/ AT produces Nox values near the maximum allowed at 15 mph, but the 25 mph values are fairly low. My past four tests (performed every two years) for Nox @ 15 mph are: 430, 471, 433, and 471 ppm. The max is 487. My Nox @ 25 mph are: 181, 176, 77, 59 ppm. The max is 774. The car just passed a smog test last week and there are no codes present, but the high Nox bothers me. Other gases are at or near the average (see attached pdf).

If anyone knows their past Nox numbers on tests they've passed, or if you have an opinion on whether I should be concerned or not please let me know.

 

For my D16Y7 on a '99 Civic, the smog station reported low single digits for NO at both measured engine speeds. O2 readings were 0.0. CO was just above 0. Everything else comparable to what you saw.

What do your fuel trims and/or O2 sensor voltages look like at both RPMs?

Mine does. Is yours not a California native?

 

Maybe the higher numbers at 15 mph are because they test that first and the converter isn't warmed up. That is mainly what the factory heat shields on the converter and front pipe are for. Usually after replacing you end up with no heat shields. Are you using the DX style combo unit or EX style separate manifold and converter?

 

Either you don't have an EGR, or you don't have a Y7. The only EGR equipped Civic model would be the HX, and that's a D16Y5 engine. EGR was equipped on the intake manifold.

 

I stand corrected. The Service Manual (page 11-254) indicates only the D16Y5 has an EGR system.

 

No problem. The motors look very similar, so I can see somebody getting confused.

 

The first of the four smog tests I show in the attachment was performed with the original DX cat/EM. Between the first and second smog test the original exhaust manifold cracked and it was replaced with a direct fit CARB compliant Magnaflow 56029. Changing the cat didn't seem to affect the smog numbers at all. I do have the original heat shield and it bolts onto the Magnaflow cat/EM just like the original, although it wasn't in place for the smog tests. I did, however, drive around for 30 min before stopping at the smog station.

I recently bought a blue-tooth scan tool for Android, but haven't bought the app. I fiddled around with the free version of Torque to check my idle rpm, but that's all I've done with it.

Thanks for sharing your smog data. Seems like I should be able to get my Nox emissions lower (for the sake of my engine and the environment). The reason I mentioned that the engine does not have an EGR system is because I thought that may explain the elevated Nox, that is, I didn't know if my car is operating as it should.

 

I checked the timing* and it was at about 6 degrees BTDC. So I advanced it as far the distributor allows and it went to 10 degrees BTDC. Spec is 12 degrees BTDC. Is that good enough or is there something else I should do to get to 12 degrees BTDC? The timing chain was replaced by the dealer about 60K mi/12 yrs ago, so I doubt mechanical timing is out of wack. Further, I adjusted the valves a year or two ago and the mechanical timing seemed to be OK.

[*Timing was performed on an engine warmed up for at least two fan cycles, service connector installed (which turned the MIL on), non-adjustable inductive timing light. Idle was within spec (700 + or - 50 rpm).]