Failed CA smog 90 civic LX after rebuild
 

Hey there. Just rebuilt a d15b2 with 160k miles. Had nothing wrong with it but wanted to increase reliability. Has been 300 miles since rebuild. Honed cylinders, new honda rings, honda bearings, all new pcv hoses, coolant hoses, every item new with oem tuneup parts.

The old engine in this actual car(not the one which was rebuilt) was burning quite a bit of oil for many many miles and used this same cat converter. I am thinking its the cat converter and o2 sensor but wanted to see if anyone else had any suggestions. The O2 sensor is from an eBay manifold, so who knows what its worth:

Full tank of Shell 87 octane, ignition timing 17
15mph test - CO2% 13.1, O2% 1.1, HC measured 184, HC max 91
CO% measured 1.23, CO% max 0.57, Nox measured 2022, nox max 835

25mph test CO2% 13.7, O2% 1.5%, HC measured 48, HC max 71,
CO% measured 0.01, CO% max 0.48, Nox measured 2781, nox max 774

Replaced cat 2 years ago with aftermarket but it burned lots and lots of oil. Do you think just a cat replacement and o2 sensor would fix the issue?

Temps are normal, new themrostat, honda coolant, no water pump, no coolant consumption.

The high NOx says possible EGR, although the low speed test with high unburned hydrocarbons could be a lot of thigs. Suggests incomplete combustion. Not sure what to make of this?

I always suspect aftermarket cats first. Second guess would be a problem causing one cylinder to run lean, pumping out nox. So then to make the O2 sensor happy, the rest of the cyls run a bit rich, pumping out some co and hc.

There ya go. That sounds plausible

its a weird one. I'm going to try and replace the cat and O2 sensor and hopefully it fixes itself.

Also it has no EGR valve

CO and HC improve at higher rpm, does it misfire or hesitate at low rpm?

It actually seems like it runs great, that's why I am confused

Failing catalytic converters? Idk. Only thing that would cause it to fail and not have the car acting weird.

The last motor burned a ton of oil so maybe that destroyed the cat?