DIY : Causes of failed smog / emissions tests
12-03-2006, 06:42 AM
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DIY : Causes of failed smog / emissions tests
This question floats on this forum quite regularly so I'm just going to post up what I go off of to give people answers. This is not a true DIY but the reason for the DIY in the topic title is to give those searching a way to distinguish from useless posts and this one. This is going to look like a clusterfuck of words, but I'll clean it up when I have a little more time.
Anyways:
The following is information to help you to understand some of the basics of smog and emissions.
<FONT COLOR="blue"><FONT SIZE="3">What is smog?</FONT></FONT>
Smog is airborne pollution. The type of smog that we're most concerned about in the automotive industry is ground level ozone. Ground level ozone is caused by Nitric oxides and Volatile Organic Compounds (VOCs). Nitric oxides are produced by your engine and gasoline is a VOC. Ground level ozone causes health problems such as asthma, immune system dysfunction, and cancer. It also is responsible for the orange haze you see in Los Angeles and we're beginning to see more often in the Bay Area.
<FONT COLOR="blue"><FONT SIZE="3">What are emissions?</FONT></FONT>
Emissions are the gasses that come out of your tailpipe. There are five automotive tailpipe emissions: Hydrocarbons, also known as HC, which is unburned gas, a contributor to ground level ozone. Carbon Monoxide, also known as CO, which is a byproduct of combustion (kind of like soot). Carbon Dioxide, also known as CO2, is a greenhouse gas which contributes to global warming. Nitric Oxides, also known as NOx, is a contributor to ground level ozone. Oxygen, also known as O2, is not bad for you or the environment. Unfortunately, only 1% of what comes out of the tailpipe is oxygen. We check the oxygen levels for diagnostic purposes.
<FONT COLOR="blue"><FONT SIZE="3">What is checked as part of a smog inspection? </FONT></FONT>
There are 3 areas of inspection: first, a visual inspection is done to make sure all of the smog equipment that is supposed to be on the car is there and properly hooked up. Next, a functional check of the timing and the EGR systems, to make sure that they are working properly. Finally there is a check of the emissions at idle and 2500 RPM. Currently only 4 of the 5 emissions are checked in our area. NOx is left out of the inspection because it is more difficult to check. Instead of checking the NOx emissions, the systems that are likely to cause high NOx are inspected during the functional check.
Update 08-02-2003 -- Now that the Bay Area is an Enhanced Area, the NOx level is inspected with the smog check.
<FONT COLOR="blue"><FONT SIZE="3">What causes high HC (hydrocarbon)?
</FONT></FONT> High HC is caused by incomplete combustion; in other words, the air and fuel that went in to the combustion chamber was not completely burned, now the unburned fuel has ended up in the tailpipe. Problems that can cause incomplete combustion include:
* An ignition misfire. If a spark plug does not spark, the air/fuel mixture in the combustion chamber does not burn and then goes out the tailpipe.
* Incorrect air fuel mixture. If there is not enough fuel in the combustion chamber to ignite, the fuel that is there goes out the tailpipe.
* Low compression. If the compression is too low the air/fuel mixture will not ignite and the unburned fuel will go out the tailpipe.
* A bad catalytic converter. The converter lives in the exhaust pipe and burns unburned gas as it passes through.
<FONT COLOR="blue"><FONT SIZE="3">What causes high CO (carbon monoxide)?</FONT></FONT> High CO is caused by a rich air/fuel mixture. The air fuel ratio should be 14.7 parts air to to 1 part fuel. Problems that can cause a rich mixture include:
* Problems with the feedback system (the system that regulates the fuel being added to the engine based on the amount of oxygen in the exhaust).
* Problems with a computer sensor such as the coolant temperature sensor, air flow meter, MAP sensor, etc..
* Problems with the fuel pressure. Fuel pressure that is too high can cause a rich mixture.
<FONT COLOR="blue"><FONT SIZE="3">What causes high CO2 (carbon dioxide)?
</FONT></FONT> High CO2 is the product of a good running engine. The better your engine runs, the more CO2 it produces. The only way to reduce CO2 emissions is to buy a fuel efficient car. The bigger your gas guzzler, the more CO2 it makes. This is what's so sad about the recent SUV trend. In addition to depleting the worlds oil reserves, and putting our country in a position where "we will go to war to protect our oil supply", the trend of building increasingly inefficient behemoths is making the planet a less hospitable place for our species (and others) by contributing to global warming.
<FONT COLOR="blue"><FONT SIZE="3">What causes high O2 (oxygen)?</FONT></FONT>
High O2 can be caused by a lean air/fuel mixture, but most of the time, noticeably high O2 is caused by either a leak in the exhaust pipe allowing air to enter, or air injection pumping air into the exhaust (this is done on some cars to aid in the burning of HC). High O2 is not a problem unless the smog machine decides the exhaust sample is too diluted to use; in which case, the car may fail the smog test for dilution.
<FONT COLOR="blue"><FONT SIZE="3">What causes high NOx (nitric oxide)?
</FONT></FONT> NOx is not measured in our area currently, but if your car is registered in an enhanced area (an area that requires testing of NOx), you may run into this problem. High NOx is caused by high combustion temperatures and pressures. Problems that can cause high NOx include:
* An inoperative EGR system. The EGR system was designed specifically to reduce NOx; that's it's only function. The EGR, which stands for Exhaust Gas Recirculation, allows exhaust gas to enter the combustion chamber through the intake. The exhaust gas has a cooling effect on the combustion chamber.
* Over advanced ignition timing. The more advanced the ignition timing, the higher the combustion chamber temperatures.
* Overheating. If the engine temperature is too high the NOx emissions will go up.
* Lean air/fuel mixture. If the air/fuel mixture is too lean the combustion temperature will go up.
* Compression over specification. Normally when we think of engines aging we think of the compression going down. However, there are a couple of ways the compression can increase as the engine is used. One is carbon buildup on the tops of the pistons. When carbon forms on the tops of the pistons, the combustion chamber area decreases and the compression ratio increases. The carbon can be manually scraped off the tops of the piston to correct this problem, but that would require disassembling the engine. Click here for cheap alternatives.
* Mysterious reasons. Sometimes NOx is too high and there's no obvious cause: the EGR works, the timing and advance work normally, the engine temperature is within range, the air fuel mixture is good, and the compression is within spec.. When this happens you can try a little tweaking. If there are two thermostats listed for the car, use the cooler one. If there are two spark plugs listed for the car, use the cooler one. Retard the timing 2 degrees (the maximum allowed). Clear out the EGR passage even if the passage seems fine. Cross your fingers.
<FONT COLOR="blue"><FONT SIZE="3">What is a Gross Polluter?</FONT></FONT>
A Gross Polluter is a vehicle that has failed the smog check by a certain amount, usually somewhere around 1.5 times the maximum allowable emissions or above. The CARB estimates that Gross Polluters cause half of all the vehicle related smog even though they only represent 10 to 15 % of the vehicles.
source: http://www.artsautomotive.com/thesmogstory.htm
Modified by FuNkDrSpOt at 1:33 AM 12/4/2006
Modified by FuNkDrSpOt at 1:34 AM 12/4/2006
Anyways:
The following is information to help you to understand some of the basics of smog and emissions.
<FONT COLOR="blue"><FONT SIZE="3">What is smog?</FONT></FONT>
Smog is airborne pollution. The type of smog that we're most concerned about in the automotive industry is ground level ozone. Ground level ozone is caused by Nitric oxides and Volatile Organic Compounds (VOCs). Nitric oxides are produced by your engine and gasoline is a VOC. Ground level ozone causes health problems such as asthma, immune system dysfunction, and cancer. It also is responsible for the orange haze you see in Los Angeles and we're beginning to see more often in the Bay Area.
<FONT COLOR="blue"><FONT SIZE="3">What are emissions?</FONT></FONT>
Emissions are the gasses that come out of your tailpipe. There are five automotive tailpipe emissions: Hydrocarbons, also known as HC, which is unburned gas, a contributor to ground level ozone. Carbon Monoxide, also known as CO, which is a byproduct of combustion (kind of like soot). Carbon Dioxide, also known as CO2, is a greenhouse gas which contributes to global warming. Nitric Oxides, also known as NOx, is a contributor to ground level ozone. Oxygen, also known as O2, is not bad for you or the environment. Unfortunately, only 1% of what comes out of the tailpipe is oxygen. We check the oxygen levels for diagnostic purposes.
<FONT COLOR="blue"><FONT SIZE="3">What is checked as part of a smog inspection? </FONT></FONT>
There are 3 areas of inspection: first, a visual inspection is done to make sure all of the smog equipment that is supposed to be on the car is there and properly hooked up. Next, a functional check of the timing and the EGR systems, to make sure that they are working properly. Finally there is a check of the emissions at idle and 2500 RPM. Currently only 4 of the 5 emissions are checked in our area. NOx is left out of the inspection because it is more difficult to check. Instead of checking the NOx emissions, the systems that are likely to cause high NOx are inspected during the functional check.
Update 08-02-2003 -- Now that the Bay Area is an Enhanced Area, the NOx level is inspected with the smog check.
<FONT COLOR="blue"><FONT SIZE="3">What causes high HC (hydrocarbon)?
</FONT></FONT> High HC is caused by incomplete combustion; in other words, the air and fuel that went in to the combustion chamber was not completely burned, now the unburned fuel has ended up in the tailpipe. Problems that can cause incomplete combustion include:
* An ignition misfire. If a spark plug does not spark, the air/fuel mixture in the combustion chamber does not burn and then goes out the tailpipe.
* Incorrect air fuel mixture. If there is not enough fuel in the combustion chamber to ignite, the fuel that is there goes out the tailpipe.
* Low compression. If the compression is too low the air/fuel mixture will not ignite and the unburned fuel will go out the tailpipe.
* A bad catalytic converter. The converter lives in the exhaust pipe and burns unburned gas as it passes through.
<FONT COLOR="blue"><FONT SIZE="3">What causes high CO (carbon monoxide)?</FONT></FONT> High CO is caused by a rich air/fuel mixture. The air fuel ratio should be 14.7 parts air to to 1 part fuel. Problems that can cause a rich mixture include:
* Problems with the feedback system (the system that regulates the fuel being added to the engine based on the amount of oxygen in the exhaust).
* Problems with a computer sensor such as the coolant temperature sensor, air flow meter, MAP sensor, etc..
* Problems with the fuel pressure. Fuel pressure that is too high can cause a rich mixture.
<FONT COLOR="blue"><FONT SIZE="3">What causes high CO2 (carbon dioxide)?
</FONT></FONT> High CO2 is the product of a good running engine. The better your engine runs, the more CO2 it produces. The only way to reduce CO2 emissions is to buy a fuel efficient car. The bigger your gas guzzler, the more CO2 it makes. This is what's so sad about the recent SUV trend. In addition to depleting the worlds oil reserves, and putting our country in a position where "we will go to war to protect our oil supply", the trend of building increasingly inefficient behemoths is making the planet a less hospitable place for our species (and others) by contributing to global warming.
<FONT COLOR="blue"><FONT SIZE="3">What causes high O2 (oxygen)?</FONT></FONT>
High O2 can be caused by a lean air/fuel mixture, but most of the time, noticeably high O2 is caused by either a leak in the exhaust pipe allowing air to enter, or air injection pumping air into the exhaust (this is done on some cars to aid in the burning of HC). High O2 is not a problem unless the smog machine decides the exhaust sample is too diluted to use; in which case, the car may fail the smog test for dilution.
<FONT COLOR="blue"><FONT SIZE="3">What causes high NOx (nitric oxide)?
</FONT></FONT> NOx is not measured in our area currently, but if your car is registered in an enhanced area (an area that requires testing of NOx), you may run into this problem. High NOx is caused by high combustion temperatures and pressures. Problems that can cause high NOx include:
* An inoperative EGR system. The EGR system was designed specifically to reduce NOx; that's it's only function. The EGR, which stands for Exhaust Gas Recirculation, allows exhaust gas to enter the combustion chamber through the intake. The exhaust gas has a cooling effect on the combustion chamber.
* Over advanced ignition timing. The more advanced the ignition timing, the higher the combustion chamber temperatures.
* Overheating. If the engine temperature is too high the NOx emissions will go up.
* Lean air/fuel mixture. If the air/fuel mixture is too lean the combustion temperature will go up.
* Compression over specification. Normally when we think of engines aging we think of the compression going down. However, there are a couple of ways the compression can increase as the engine is used. One is carbon buildup on the tops of the pistons. When carbon forms on the tops of the pistons, the combustion chamber area decreases and the compression ratio increases. The carbon can be manually scraped off the tops of the piston to correct this problem, but that would require disassembling the engine. Click here for cheap alternatives.
* Mysterious reasons. Sometimes NOx is too high and there's no obvious cause: the EGR works, the timing and advance work normally, the engine temperature is within range, the air fuel mixture is good, and the compression is within spec.. When this happens you can try a little tweaking. If there are two thermostats listed for the car, use the cooler one. If there are two spark plugs listed for the car, use the cooler one. Retard the timing 2 degrees (the maximum allowed). Clear out the EGR passage even if the passage seems fine. Cross your fingers.
<FONT COLOR="blue"><FONT SIZE="3">What is a Gross Polluter?</FONT></FONT>
A Gross Polluter is a vehicle that has failed the smog check by a certain amount, usually somewhere around 1.5 times the maximum allowable emissions or above. The CARB estimates that Gross Polluters cause half of all the vehicle related smog even though they only represent 10 to 15 % of the vehicles.
source: http://www.artsautomotive.com/thesmogstory.htm
Modified by FuNkDrSpOt at 1:33 AM 12/4/2006
Modified by FuNkDrSpOt at 1:34 AM 12/4/2006
12-03-2006, 07:06 AM
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Re: (axtran)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by axtran »</TD></TR><TR><TD CLASS="quote">i know this already but still interesting for many people who don't understand what is going on. CA has to make it hard for everyone 
</TD></TR></TABLE>
Well this post obviously isn't for people who already know it, smart ***
. I'm just slowing the flood of "why did my car fail emissions" posts.
CA doesn't really make it hard. Smog tests are a good thing. THe only thing that sucks about smog is that you should be able to make as many mods to your car as you want, as long as you can PASS SMOG, not show that you have some arbitrary sticker that some performance company bought from CARB.
</TD></TR></TABLE>Well this post obviously isn't for people who already know it, smart ***
. I'm just slowing the flood of "why did my car fail emissions" posts.CA doesn't really make it hard. Smog tests are a good thing. THe only thing that sucks about smog is that you should be able to make as many mods to your car as you want, as long as you can PASS SMOG, not show that you have some arbitrary sticker that some performance company bought from CARB.
12-04-2006, 05:41 AM
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Re: DIY : Causes of failed smog / emissions tests (FuNkDrSpOt)
Nice post ....This is something that most of us on the east coast don't have to worry about we have some emission testing but nothing like CA. However if the bill passes PA is talking about making emission laws that are as strict as CA.
12-04-2006, 07:59 AM
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its more of an issue here. i still see 81 corollas rollin around LA putting black smoke into the air and i wonder sometimes why i am always paranoid of maintenance
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12-04-2006, 08:11 AM
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12-07-2006, 10:43 PM
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Re: (Duane_in_Japan)
That's not true. What you mean to say is that if you have low income you can qualify to have the smog repairs up to a certain cost paid by the state. You usually pay a deductible. If you want the exact details I can break out my paper work.
This post is good start but I'd like to see some Honda specific troubleshooting or recommended course of action for each of the "what causes..." topics.
Smog/oil change/tune up shops just want to sell you an O2 sensor and a cat converter, then if it still fails, they either charge you up the *** and keep throwing parts at it, or they throw their hands up.
This post is good start but I'd like to see some Honda specific troubleshooting or recommended course of action for each of the "what causes..." topics.
Smog/oil change/tune up shops just want to sell you an O2 sensor and a cat converter, then if it still fails, they either charge you up the *** and keep throwing parts at it, or they throw their hands up.
12-07-2006, 11:55 PM
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Re: DIY : Causes of failed smog / emissions tests (FuNkDrSpOt)
good info... im no mod but im pretty sure you can only have standard size font in your sig... im not haten just dont want you to get droped to 98%... 
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