Hi All,

1996 850 w/ approx 200k. California Smog Test: On the low speed test, I have 0 NOx. At 25mph however, my NOx shoots through the roof.

I followed a local mechanics advice and replaced both O2 sensors. I went back to get another smog check, and my HC went down a bit, but my NOx got even worse! (see below)

-My 850 does NOT have an EGR valve. The air-intake valve is working correctly (tested it in the freezer).
-I've been throwing the P0410 code for a while but haven't been too worried about it (secondary air injection system) in regards to smog.
-I was checking the flame trap and noticed a split in one of the vacuum hoses leading up to the trap. The trap itself was very greasy. I suspect the PCV system is pretty gunky - could this alone be responsible for such high numbers?

-With high NOx, I've been told the car is running lean and hot: Should I consider replacing thermostat?

Big question: Could a bad CAT alone be responsible for such a high NOX reading?

(please see pics for smog readings before and after O2 sensor replacement)

 

Hi and welcome to the forum.

I would start with the PCV system replacement. That is the cause of a lot of crankcase and vacuum problems. Then you can try to clean out the cat by running some lacqure thinner through the gas tank at the rate of 10/1 mix. Ten gallons of gas and 1 gallon of lacqure thinner. If you to that, drive the car for about 200 miles to run most of the gas out then gas up again to protect the fuel system.

You'll also have to drive enough to get the READY notice in the OBD-II system.

 

Hey RSPI,

Thanks for the reply!

I just confirmed a vacuum leak at the flame trap with some carb cleaner, and also visualized smoke from the dip stick.

Would a gunked PCV system be sufficient to explain / effect the high NOx readings?

Thanks all