How to lower NOx emissions
June 6, 2006 6:10 AM Subscribe
Is there anything I can do, without the help of a mechanic, to lower my car's NOx emissions by ~60ppm?
My '93 Cutlass Supreme only just failed the NOx part of its required emissions test. (Driveclean.) It passed the HC and CO no problem.
To get a pass for the NOx emissions as well, every mechanic I've talked to wants to start with a $100 diagnostic test. If the emissions were way over, I'd do the test and get whatever repairs are required (clean air, and all.) But the mitigating factors here are: 1) it failed by only 60ppm, and 2) I'll be selling the car before the end of the year. I don't want to spend a penny on it if I don't have to.
Is there anything I can do myself to reduce the NOx emissions? I'm pretty sure the Cutlass Supreme's timing is computer controlled, so that's probably not an option. What about the fuel/air mix? Is there any way I can adjust that myself? Or what about simpler options like fuel additives?
Some other quick notes:
- I had the air filter and oil changed last week.
- The catalytic converter was replaced 18 months ago, and has less than 20,000 miles on it.
- For all the good it did, I ran one of those "guaranteed to pass" products through a full tank of gas, and filled up with Sunoco 94 before the test.
My '93 Cutlass Supreme only just failed the NOx part of its required emissions test. (Driveclean.) It passed the HC and CO no problem.
To get a pass for the NOx emissions as well, every mechanic I've talked to wants to start with a $100 diagnostic test. If the emissions were way over, I'd do the test and get whatever repairs are required (clean air, and all.) But the mitigating factors here are: 1) it failed by only 60ppm, and 2) I'll be selling the car before the end of the year. I don't want to spend a penny on it if I don't have to.
Is there anything I can do myself to reduce the NOx emissions? I'm pretty sure the Cutlass Supreme's timing is computer controlled, so that's probably not an option. What about the fuel/air mix? Is there any way I can adjust that myself? Or what about simpler options like fuel additives?
Some other quick notes:
- I had the air filter and oil changed last week.
- The catalytic converter was replaced 18 months ago, and has less than 20,000 miles on it.
- For all the good it did, I ran one of those "guaranteed to pass" products through a full tank of gas, and filled up with Sunoco 94 before the test.
Response by poster: Ya, I took it on the highway for half an hour, and left it idling at the testing center while I waited.
posted by ParsonWreck at 6:23 AM on June 6, 2006
posted by ParsonWreck at 6:23 AM on June 6, 2006
NOx is generally the result of really high temperature exhaust. Being the son of a mechanic, it is difficult for me to say what is beyond the scope of most individuals. I would richen the mixture slightly to lower temperatures, or advance the timing slightly. I think that will cool the engine down enough. A 30 minute run on the highway straight onto the test dyno would likely help if you can arrange it.
On preview: try to book the test for first one of the day or slip the mechanic a $10er to get it right on there off the highway.
posted by KevCed at 6:50 AM on June 6, 2006
On preview: try to book the test for first one of the day or slip the mechanic a $10er to get it right on there off the highway.
posted by KevCed at 6:50 AM on June 6, 2006
or advance the timing slightly.
You mean retard the timing?
Parson, just because the timing is electronically controlled doesn't mean you can't adjust it. There is usually a base timing setting that is used as a starting point, which is adjustable by turning the distributor. Of course, I don't know about your particular car, but this is what I know from my cars. Good luck trying to tune your emissions in your driveway without a sniffer test though.
Does your car have multiple cats? Usually there is a primary and a secondary, at least. If you've replaced one, consider replacing the other. Replacing cats is the only reliable way I've seen to lower NOx emissions.
posted by knave at 7:34 AM on June 6, 2006
You mean retard the timing?
Parson, just because the timing is electronically controlled doesn't mean you can't adjust it. There is usually a base timing setting that is used as a starting point, which is adjustable by turning the distributor. Of course, I don't know about your particular car, but this is what I know from my cars. Good luck trying to tune your emissions in your driveway without a sniffer test though.
Does your car have multiple cats? Usually there is a primary and a secondary, at least. If you've replaced one, consider replacing the other. Replacing cats is the only reliable way I've seen to lower NOx emissions.
posted by knave at 7:34 AM on June 6, 2006
Richening the mixture, even if it does lower NOX, may adversely affect the HC/CO numbers
posted by Pressed Rat at 9:27 AM on June 6, 2006
posted by Pressed Rat at 9:27 AM on June 6, 2006
This car has closed loop fuel control - you can't richen the mixture without changing the calibration prom. Also, many cars in this time frame didn't have distributors, and do not have a way to adjust spark timing. You might check to make sure your EGR valve is working (if equipped).
posted by rfs at 10:20 AM on June 6, 2006
posted by rfs at 10:20 AM on June 6, 2006
Response by poster: For future searchers, here's what I did to get a pass:
First, high-octance gas, at least the Sunoco stuff with ethanol added, was a poor choice to reduce my NOx levels. A couple of references:
"The downside of gasohol use can be increased emissions of nitrogen oxides (NOx)"
"The auto/oil study concluded that there was a statistically significant increase in NOx of about 5% with the addition of 10% ethanol."
Second, I found info how to clean the EGR valve myself. (Instructions are specific to my Cutlass, though:)
Autozone
About.com
Finally, I ran a can of carb and fuel line cleaner through the system, filled up with regular (87 octance) gas, and re-tested.
I passed, just barely. But hey!
posted by ParsonWreck at 6:48 AM on June 21, 2006
First, high-octance gas, at least the Sunoco stuff with ethanol added, was a poor choice to reduce my NOx levels. A couple of references:
Second, I found info how to clean the EGR valve myself. (Instructions are specific to my Cutlass, though:)
Finally, I ran a can of carb and fuel line cleaner through the system, filled up with regular (87 octance) gas, and re-tested.
I passed, just barely. But hey!
posted by ParsonWreck at 6:48 AM on June 21, 2006
This thread is closed to new comments.
posted by croutonsupafreak at 6:18 AM on June 6, 2006