Ca. Smog High Nox
Thread Starter
Racer
Joined: Jun 2011
Posts: 283
Likes: 5
Ca. Smog High Nox
Hi everyone. Well, just failed smog check for the first time. All the numbers look great except the NOX at 15mph. CO2=0.0 @ 15 & 25 mph, HC=1 @15 & 25 mph and CO=0.0 @ 15 & 25 mph. This is the results for the NOX which I failed. NOX = 612 @ 15mph FAIL and NOX=705 @ 25 mph barely pass. No codes but I'm thinking it's either egr valve, egr solenoid or the passages might have some carbon build up. The egr valve and solenoid were changed 2 years ago. I will check both the valve and solenoid but I want to clean the passages also. What's the best way to clean the passages and could there be something else I'm missing?
Safety Car
Joined: Jun 2003
Posts: 4,250
Likes: 656
From: San Diego Ca
An owner of a local STAR smog station (individually owned but qualified by California to do smogs of high emissions vehicles) told me that the first thing to do when faced with a near pass, but fail condition is to replace the Oxygen Sensors. If you have the same one wire AFS 21 my 93 has they are $14 each and only need a 7/8ths inch wrench to replace although special sensor sockets are available.
After that you might datalog the car to see that it is in fact controlling near the Stoich Point and not running particularly lean or particilarly rich. If lean it robs the exhaust of oxygen needed for the converter to reduce the NOx.
After all that you can replace the converters. I did it back in the day when you could find a low mileage C4 in the junkyard with really good cats. Don't know about that supply these days.
Perry
After that you might datalog the car to see that it is in fact controlling near the Stoich Point and not running particularly lean or particilarly rich. If lean it robs the exhaust of oxygen needed for the converter to reduce the NOx.
After all that you can replace the converters. I did it back in the day when you could find a low mileage C4 in the junkyard with really good cats. Don't know about that supply these days.
Perry
Thread Starter
Racer
Joined: Jun 2011
Posts: 283
Likes: 5
An owner of a local STAR smog station (individually owned but qualified by California to do smogs of high emissions vehicles) told me that the first thing to do when faced with a near pass, but fail condition is to replace the Oxygen Sensors. If you have the same one wire AFS 21 my 93 has they are $14 each and only need a 7/8ths inch wrench to replace although special sensor sockets are available.
After that you might datalog the car to see that it is in fact controlling near the Stoich Point and not running particularly lean or particilarly rich. If lean it robs the exhaust of oxygen needed for the converter to reduce the NOx.
After all that you can replace the converters. I did it back in the day when you could find a low mileage C4 in the junkyard with really good cats. Don't know about that supply these days.
Perry
After that you might datalog the car to see that it is in fact controlling near the Stoich Point and not running particularly lean or particilarly rich. If lean it robs the exhaust of oxygen needed for the converter to reduce the NOx.
After all that you can replace the converters. I did it back in the day when you could find a low mileage C4 in the junkyard with really good cats. Don't know about that supply these days.
Perry
Safety Car
Joined: Jun 2003
Posts: 4,250
Likes: 656
From: San Diego Ca
The fact that they were allowing oxidation take place certainly would indicate that. But the NOx removal is a reduction step and takes even more oxygen. However I would not redo the cats lightly. My point was that at $28 and shipping, 2 sensors are a trivial thing. I don't even know if that recommendation was a good one, but the guy had been owning a smog station in Ca a long time, so I have decided to take his advice and ordered 4 sensors for both my 93s.
I can't mention my vendor at that price as they don't pay this forum, but it was a simple parts search on Google for the AFS 21 one wire sensors
I can't mention my vendor at that price as they don't pay this forum, but it was a simple parts search on Google for the AFS 21 one wire sensors
Thread Starter
Racer
Joined: Jun 2011
Posts: 283
Likes: 5
The fact that they were allowing oxidation take place certainly would indicate that. But the NOx removal is a reduction step and takes even more oxygen. However I would not redo the cats lightly. My point was that at $28 and shipping, 2 sensors are a trivial thing. I don't even know if that recommendation was a good one, but the guy had been owning a smog station in Ca a long time, so I have decided to take his advice and ordered 4 sensors for both my 93s.
I can't mention my vendor at that price as they don't pay this forum, but it was a simple parts search on Google for the AFS 21 one wire sensors
I can't mention my vendor at that price as they don't pay this forum, but it was a simple parts search on Google for the AFS 21 one wire sensors
Melting Slicks
Joined: Apr 2001
Posts: 2,115
Likes: 221
From: Ca.
Pull it off and actually test it.
I applied vacuum to the in port (with brake bleeder) and a vacuum gauge to the out port; and applied ground and power to the leads to really test it.
I went thru 3 new that all had various types of shorts/malfunctions before I found a used one that actually worked.
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Thread Starter
Racer
Joined: Jun 2011
Posts: 283
Likes: 5
Odds are your egr solenoid is not working. (been there/done that!)
Pull it off and actually test it.
I applied vacuum to the in port (with brake bleeder) and a vacuum gauge to the out port; and applied ground and power to the leads to really test it.
I went thru 3 new that all had various types of shorts/malfunctions before I found a used one that actually worked.
Pull it off and actually test it.
I applied vacuum to the in port (with brake bleeder) and a vacuum gauge to the out port; and applied ground and power to the leads to really test it.
I went thru 3 new that all had various types of shorts/malfunctions before I found a used one that actually worked.
Melting Slicks
Joined: Apr 2001
Posts: 2,115
Likes: 221
From: Ca.
It's the solenoid that controls the vacuum to the egr that I have found the main problems with.
Thread Starter
Racer
Joined: Jun 2011
Posts: 283
Likes: 5
Yeah, I'm in San Francisco, California. I just changed the egr valve and the old one's diaphragm seemed a little stiff but I'm beginning to think it might also be the solenoid. I have the solenoid ordered and should get here in a couple of days. Decided to change the egr valve, solenoid and vacuum hoses because the cost for all parts are under $80 and that way I can cover all the bases.
Burning Brakes
Joined: Apr 2012
Posts: 888
Likes: 4
From: Ridgecrest Ca
High NOX at low speed usually indicates lean running. The EGR won't open or begin opening until about 1800 - 2000 rpm. You ought to look at the 02 sensors. It's fairly easy to test the EGR.
Melting Slicks
Joined: Apr 2001
Posts: 2,115
Likes: 221
From: Ca.
In Cali they run it at 15mph and 25mph loaded on a dyno, so rpms are usually 1500 to 1800 rpm depending on your gearing.
Kali smog is a pia-if you burn your own proms it makes it easier-really necessary with mods.
And yes if too lean the nox goes up.
You should buy a scan tool that will show live data also, not just codes-see what blms are. You'll probably wonder how you ever got along without the scan tool after you have it a while!
Thread Starter
Racer
Joined: Jun 2011
Posts: 283
Likes: 5
Actually if you look at the code in the bins egr begins at 1200 rpm.
In Cali they run it at 15mph and 25mph loaded on a dyno, so rpms are usually 1500 to 1800 rpm depending on your gearing.
Kali smog is a pia-if you burn your own proms it makes it easier-really necessary with mods.
And yes if too lean the nox goes up.
You should buy a scan tool that will show live data also, not just codes-see what blms are. You'll probably wonder how you ever got along without the scan tool after you have it a while!
In Cali they run it at 15mph and 25mph loaded on a dyno, so rpms are usually 1500 to 1800 rpm depending on your gearing.
Kali smog is a pia-if you burn your own proms it makes it easier-really necessary with mods.
And yes if too lean the nox goes up.
You should buy a scan tool that will show live data also, not just codes-see what blms are. You'll probably wonder how you ever got along without the scan tool after you have it a while!