TowerCrisis

Heya folks. I just did a smog test to verify if everything was in working order on my 1997 NA. Unfortunately, test results were as follows and failed CA smog on my newly built engine. I've put ~2000 miles on the car since installing this new motor.

@ 15mph
Co2: 14.5 O2: 2.4 HC: 32 CO: 0.00 NOx: 700

@ 25mph
Co2: 14.8 O2: 1.8 HC: 49 CO: 0.00 NOx: 557

Now here's where things get a little funky. I'm running naturally aspirated on 8:1 pistons, with a 1.3mm head gasket. So my CR is very low to begin with. I'm running 12 degrees timing. Stock cams with VS855's. K&N drop in stock airbox filter. Stock EGR system. With a Cobalt 4-2-1 header. Magnaflow CA compliant CAT. And from my understanding I don't have a huge vacuum leak, but I might have to look harder. I additionally had a mishap a couple months ago where I drove ~15 highway miles with my primary O2 sensor unplugged. My understanding is that these numbers imply a very lean run condition.

What should my next moves be? I've gotten advice to replace my O2 sensor next, not sure what I should try out and know the dangers of throwing new parts at a problem.

And yes, I know I'm stupid for running low comp pistons naturally aspirated. It will be boosted once I get this thing running well and take care of other fronts.

thebeerbaron

iTrader: (1)

Which of those values were failures? I don't recall what CA is expecting these days. I think everything except the NOx looks good, but that's just my (failing) memory.

Isn't stock timing 10 degrees? I'm surprised those couple of degrees would cause a failure, but what do I know. I'd definitely set that back to stock.

It's a 97 and you're running the stock ECU? Are there any emissions-related codes?

sonofthehill

iTrader: (1)

You are right at the max HC for 25 but 15 is fine. Then the NOx is high on the 15 but acceptable on the 25. I think it suggests that you are a little bit lean but as the baron pointed out 2 degrees might just make the difference. I might also consider a fuel filter or perhaps a tired pump. A fresh oil change might bring the HC down a bit, but it might not. Also I always use fresh plugs, the stock spec.

TowerCrisis

Ah I should have clarified. CA limits are as follows
@ 15mph limit
HC: 66 CO: 0.57 NOx: 487

@ 25mph limit
HC: 49 CO: 0.55 NOx: 774

My HC and CO are quite low, and I'm happy with where they're at. NOx seems unreasonably high. On my original motor it was only ~20% of the max, and the cat is only a couple years old. I do worry that somehow the car is running in open loop mode all the time. Is there a way to check that?

I'll verify my ignition timing and set it to 10. Additionally this car's on the stock ECU, stock injectors.

patsmx5

iTrader: (16)

Going off memory but I think less timing will improve things.

Ted75zcar

iTrader: (2)

Check your base timing. Here is a nifty table for you.