Trouble shooting high NO emission - 96 855 NA

Post by **jdw** » 18 Jan 2010, 19:46

I would like some advise on an emission problem with my '96 850 wagon. It is a GLT non-turbo with manual transmission and 130K miles.

The NO at 25 mph measured 2326 ppm (max = 717). At 15 mph it measured 399 ppm (max = 430). The NO was high, but below limits, on previous bi-annual inspections as well. This prompted me for requesting a pre-inspection today.

The CO% measures 0.09 (max = 0.50) at 15 mph and 0.00 (max = 0.47) at 25 mph.

My CEL occasionally comes on with code P0410. The air pump runs strong. I have not checked the SAS valve. The light resets every time and stays off for about a month.

The smog tech suggested a new cat and new O2 sensors. I think they have never been replaced on the car. Is there anything else I should check before opening my check book? Also how does the inspector verify if the catalytic converter is certified for California use?

Thanks.

Post by **jblackburn** » 18 Jan 2010, 21:02

New cat? I call shenanigans.

The P0410 code is definitely for the air pump. If the air pump runs, I'd check out the vacuum line and the SAS valve itself - these things are junk by design and start to leak, and if you catch it in time, you can probably save the air pump.

Drill holes in the bottom of the air pump housing to let out kempt-up moisture.

I know nothing about emission numbers, but it's possible the front O2 sensor may need to be replaced if those are high. The rear one only reads the numbers coming out of the cat. Were these numbers taken with the engine warmed up completely? How's your gas mileage?

A bad coolant temperature sensor can cause the car to use a lot of gas as well, and would account for high emissions. My car blew black smoke occasionally when its went bad. Have you noticed the temp gauge doing anything funny?

Both of these can throw codes, but sometimes won't.

Post by **jdw** » 18 Jan 2010, 22:39

Thank you jablackburn.

My mileage has dropped from ~25 when new to maybe ~21 mpg now but I also move to area with some hills. The car was fully warmed up when tested.

I'm also reading that NOx level can get bad if the EGR system is clogged up. I'll look at that as well.

Thx. JD.

Post by **jdw** » 30 Jan 2010, 19:22

My car failed it's second California smog check today. This time NO levels exceeded both the 15 and 25 mph limits. The emissions were even higher regardless of a new cat.

- Temperature gauge looks normal
- Car does not have EGR system
- I could not find any obvious vacuum leaks
- Throttle body was clean
- Engine is stock with exception for the 960 throttle plate
- Two new O2 sensors (never shown any codes)
- New CA certified universal Magnaflow 46006 catalytic converter
- Mileage near normal
- Engine was warm during test
- Intake hoses seem properly connected
- Timing belt recently replaced

I suspect that the PCV system needs to be cleaned/replaced. It hasn't been touched in 132K. The dipstick hole does smoke a little. I understand that a clogged PCV may cause too high temperatures causing high NO levels.

The PCV replacement instructions scare me a little. Does anyone have any other recommendations before I replace it?
Thanks.

Post by **polskamafia mjl** » 30 Jan 2010, 19:25

What kind of gas are you using?

Post by **jdw** » 30 Jan 2010, 19:55

I use premium in the months when I have to go through smog.

Plugs, wires, distributor are about 10k old. Recent oil change.

rcannon · Post by **rcannon** » 30 Jan 2010, 22:26

Generally NOx goes up as timing is advanced. Maybe regular gas would cause it to retard the timing and reduce NOx. Do you ever get any pinging? If so maybe the knock sensor is bad or something, causing too advanced timing. Don't know for sure about Volvos. And could your timing be off if your cam was off a tooth, since it drives the distributor? Or if a cam is off a tooth, that could affect air flow timing and NOx I suppose.