How to help pass NOX for smog test S13

[92sxCalifornia]

Here are a couple of things that might help NOX.

I failed NOX on stock S13 after doing all the regular things, EGR working, Sea Foam, warm engine, RXP, etc. Don’t want to take everything apart for a real de-carbon.

I always had a broken detonation sensor and passed smog, but I had fixed that recently. But does a working DET help, or hurt? A failed detonation sensor (code 34) does not trigger the MIL light, and the engine compensates by retarding the timing. Retarded timing helps NOX.

I passed the next smog test by doing 2 things. I pulled the detonation cable (actually electrical taped it to look intact) and I got aggressive with the timing, setting it at -15 with a timing light. Weird, Consultan reported -20, and the smog shop showed -19 (they check in CA). Whatever, it worked.

Anyway, maybe you can consider this for your NOX arsenal.

[WDRacing]

Ignition timing has a sweet spot where the combustion process becomes the most efficient. Playing with ignition timing is definitely something you can do to pass emissions.

What I found odd was that your ecu is pulling timing. It shouldn't unless you're getting knock.

[92sxCalifornia]

My understanding is that with the DET connected, the ECU will attempt to keep timing efficiently advanced until the sensor hears a knock under load. Then it backs off timing under acceleration (or cruising?) just enough to prevent knocks. When the sensor is defective (code 34), the ECU makes a more global timing adjustment when the engine is under load to ensure no damage to the engine. Performance and fuel economy suffer, but maybe NOX benefits on the dyno.

All said, I don't know for sure that disconnecting the sensor made the difference, I just know that the one time I tested with a working sensor I failed. I'll disconnect it for future tests as a precaution.