- Wed Jun 25, 2008 9:29 pm
#59785
**2016 edit ALL THE HELP I CAN PROVIDE IS NOW CONTAINED IN THIS FIRST POST
Here is a very basic rundown of smog failures and how you should address them on an OBD1 Honda. Essentially if you fail smog, you are not getting the most from your engine. Every effort should be made to pass smog legitimately because the end result is better performance, better fuel economy, better reliability, and less stress on the environment.
I am a certified I/M and Safety tech in the state of Utah where the ASM (dyno) test is required for OBD1 cars. I'm also very familiar with CA smog having lived there until recently.
Diagnosing an emissions issue requires looking at ALL of your gasses, not just the regulated gasses. Without analyzing CO2 and O2 readings, you cannot tell why the engine is running incorrectly.
CO Fail
High CO (above .1%) is caused by running rich. Besides failing smog, running rich reduces power and fuel economy, wears out your cat converter, and harms your O2 sensor. Running rich is commonly caused by a bad fuel pressure regulator (check vacuum and return line), aftermarket fpr, bad, clogged, or incorrect injectors for the application, bad O2 sensor, bad, missing, or tampered thermostat causing you to run cold, clogged air filter, chipped ECU, altered or tampered sensor wiring, etc.
HC Fail
There are two main causes of HC fails: air fuel ratio off, or weak ignition. %O2 and %CO will indicate a problem with air fuel ratio. %O2 above a couple % indicates you're running lean. If the idle speed is high, you have a vacuum leak. Check hoses and gaskets. If Idle is normal, check your fuel filter and O2 sensor. If %O2 is 0 and CO is high (.5 or higher), then you're running rich. Check your fpr, air filter, O2 sensor. Note that the O2 sensor can be weak and not throw a code. Remove it and clean it with a torch, wire brush, and compressed air. If it's old, just replace it.
If %O2 is near 0 and CO% is .0x or lower, then your problem is most likely a weak ignition system. Less commonly it could be low or uneven compression. Check your ignition rotor, distributor cap, spark plugs, ignition timing. Mist water over the spark plug wires with the engine running in the dark. If they're bad, you'll see sparks. If all these check out, get a multimeter and check the ignition coil and ignitor inside the distributor. If those are within spec, do a compression test. You can sometimes improve compression with a valve adjustment. Sometimes you have a burnt valve or worn piston rings.
Also make sure you are running the correct octane for the engine. SOHC Honda engines run best on 87 octane but have trouble burning 91. B Series VTEC motors have higher compression ratios and benefit from 91 octane.
NOx Fail
High NOx is caused by very hot combustion (1800-2500 F). Most Hondas do not have EGR (EGR cools the combustion chamber) except for Accords, the VTEC-E motors and 99 and later motors ie D17A, late D16Y8. When the EGR fails it most often is clogged on the intake side.
High coolant temps are often times the cause of high NOx for us. The gauge may indicate a normal temperature however I have found that it will give the same reading from 180-220 degrees F! A better indicator is that your radiator fan comes on often and stays on for a long period of time. An even better indicator is a pyrometer. Make sure the smog tech is using the dyno fan. Try flushing your coolant system at both the radiator and through the thermostat housing. One way to artificially increase the efficiency of your coolant system is to install a higher pressure radiator cap (stay within a few PSI of the stock rating). Just be aware that doing so will cause all your old hoses to blow. Silicon hoses are a very nice upgrade. Another option in non freezing climates is to run a slightly higher water concentration than the recommended 50/50 mix. Many people choose to run bigger and thicker radiators but this is usually overkill for non turbo applications.
JDM motors tend to have higher NOx emissions possibly due to their slightly higher compression. Retard the ignition timing to the low side of spec and run high octane. Seafoam the combustion chamber and make sure the coolant system is operating at its best. High NOx are also caused by lean mixtures (up to about 16.5:1 after which NOx levels tend to fall off). Check the O2 sensor, fuel filter, fuel pump strainer, and fuel pump.
NOx feeds back on itself meaning the NOx causes runaway NOx, often resulting in readings of 2000+. If your readings are this high it's a good indication that simply replacing the cat converter isn't going to be enough.
Catalytic Converter
Catalytic converters are the 2nd highest oversold item (meaning that good cat converters are often times replaced w/out cause). Repair shops love to replace catalytic converters because they are a high price item so there's a big margin. Often times a fresh cat converter will mask an engine problem and get you to pass smog, but the underlying problem will then destroy the cat converter so that you need to replace it again at your next smog check. Federal law requires that they are warrantied not to fail for at least 8 years or 80,000 miles (on a properly running engine). For this reason I recommend doing a complete tune-up and replacing the cat converter only as a last resort.
Catalytic converters should never wear out. Some things that kill cat converters or cause it not to work properly are 1) dropping it/scraping it, 2) running rich (overheats it and melts the precious metals inside) 3) Silicone (gives off a gas when hot which will temporarily coat the precious metals but will later burn off) 4) Phosphorus (from crappy oil or gas and from not changing the oil regularly).
Many times when your cat converter is not working efficiently you can remove it and blast the insides with a torch. It will give off some bright green and blue flames.
If your cat converter turns out to be bad, you can recycle it for about $20-30.
Properly Diagnosing the Cat Converter
The best way to test your cat converter is to first test your tail pipe emissions. Then drill a 3/16 hole in your exhaust pipe before the cat. Install the auxilliary adapter to the smog test probe and insert it in the hole. Measure the emissions and compare them to your previous reading. Comparing the pre and post cat readings will tell you its efficiency. OBD2 cars have an O2 sensor before an after the cat for this purpose.
O2 Sensor
O2 sensors greatly affect your AFR ratio because they are used for AFR feedback. A bad O2 sensor causing you to run rich will hurt your power in the driving range (WOT is unaffected unless you're in limp mode from a catastrophic O2 sensor failure). A bad O2 sensor causing you to run overly lean can cause additional stress on your engine. The most common symptom of a bad or lazy O2 sensor is hesitation, loss of power, and loss of fuel economy.
Note that under heavy load conditions (heavy and wide open throttle), O2 feedback is ignored and the ECU reads from a fuel table. This is why having your car dyno tuned can result in a significant power increase.
O2 Sensors are a maintenance part and will wear out and "get lazy" over time. Most times it will not cause a check engine light unless it's a catastrophic failure. You can test O2 sensors for laziness using a digital multimeter. The procedure can be found in the repair manual. Do not replace the O2 sensor w/out first verifying that it is bad. If your O2 sensor fails prematurely it's probably due to a blown headgasket (burning coolant), bad piston rings (burning oil), or running rich. Some types of engine cleaners and liquid gaskets can harm O2 sensors as well.
O2 and CO2 as Indicators
A good running engine will have low O2 (near zero) and high CO2 (near 14.9). There should be almost no O2 reading unless you have an air injected cat converter (S2000?). If you have a lot of O2, you're running lean. O2 can sometimes be caused by an exhaust leak.
Full Tune-Up
Besides the regular tune up items (distributor cap, rotor, spark plugs, synthetic oil change, base ignition timing, tire pressure, air filter, PCV) you should also perform the following according to the maintenance schedule: fuel filter, fuel pump strainer (inside fuel tank), have your injectors balanced/blueprinted (especially on JDM imports), remove and clean out your throttle body, IACV, and intake manifold. Adjust the slack in the throttle cable and a/t cable. Seafoam the motor a few dozen miles before you change the oil and filter spark plugs and O2 sensor if applicable. Check plug wires. Test O2 sensor with a multimeter. Some states have begun testing charcoal canisters. Your fuel cap may need to be replaced if it fails the test.
Effect on the Environment
NOx
Oxides of Nitrogen cause a nasty haze above cities that carries over into many famous wilderness areas ie the Grand Canyon. It combines with industrial emissions and hydrocarbons from cars to cause acid rain. It causes eutrophication which kills fish and degrades water quality. It creates particulate matter small enough to bypass the tiny hair follicles in your throat and embed directly into your lung tissue causing cancer. Most NOx emissions come from power plants and diesel engines.
CO2
Carbon Dioxide is a greenhouse gas and a cause of climate change. Plants convert CO2 into sugar and O2 but cannot keep up with the amount we are generating. An effort needs to be made to limit the amount of CO2 emitted in the atmosphere so that the plants and plankton in the ocean can handle it so the world is still livable for puppies and children.
CO
Carbon Monoxide is clear, odorless, and poisonous. It gets into your blood displacing the oxygen and stays there until the blood cells die. Over time, CO accumulates in your system causing you to be forgetful, feel lazy, and have headaches. It also contributes to global warming.
Interestingly, the most effective regulation to reduce air pollution has been the requirement to test gas caps. A bad gas cap will cause many times as much pollution as a car that failed on HC's. The worst part about a bad gas cap is that the car doesn't even have to be running to emit pollution.
2014 edit (taken from page 4)
So for background info I posted this thread in 2008 and haven't worked in safety/emissions in over 4 years. Honestly, when I have an emissions problem I'll often reference this thread, as I often reference some of my other threads on other sites for other info and of course my own damn website I never imagined I would still be messing with Hondas and answering questions on forums 6 years later (got into the game in 2002 actually) but I just bought another VX winter 2013 and this is a great little community so here goes:
EVERYONE IN THIS THREAD SHOULD READ THIS
These cars are all over 20 years old and in the hundreds of thousands of miles. A simple tune up (oil, spark plugs, rotor, cap, PCV, check wires, ignition timing, fuel filter, check O2 sensor, check idle speed) just doesn't cut it anymore. If you haven't even gotten this far, put away your smart phone and come back when you have.
(On your VX make sure you have the right spark plugs in there and only use NGK or dealer plugs. Most VXs have the wrong ones since the application is often incorrect and most parts stores stopped carrying the correct plugs (try amazon).)
After the basics, you still need to do some reconditioning before you can even get a baseline for diagnosis.
All VX's and most other models need the intake manifold removed and thoroughly cleaned, especially around the EGR ports. Remove the MAP sensor as it is sensitive to cleaners and solvents. You'll need a new throttle body gasket and intake manifold gasket and you can't count on the bigger auto parts chain stores having them anymore. Oven cleaner works reasonably well for cleaning baked on gunk, but it will still require a lot of soaking and brushing. Aircraft remover helps get the old gasket off along with a razorblade scraper and a fine grit sand paper on a grinder. Also clean the head ports and injector holes a bit but don't get a bunch of gunk into the cylinders and don't spray too much throttle body cleaner in there or you'll have a fun time drying it out so it can start again. While you have the manifold off, pull the breather box off, clean it out and replace the O ring to the block. You'll need the exact right size O ring.
All EGs need fuel injector service. I like Injector Rehab. VXs and CXs have smaller injectors than all other D and B series (which are all 240CC) so keep this in mind if you plan to send junkyard injectors in to minimize downtime.
All EGs need valve adjustments (see my other thread). You will find that each valve is inconsistent with the next and that the intake side is often too tight and the exhaust side too loose. This is wasted power potential, wasted gas, preventable emissions, premature death for your O2 sensor and cat converter, and it's hard on your engine because some cylinders are running rich and others lean.
Put 1/3rd can of Seafoam in the fuel tank, oil, and suck the other 1/3rd in the brake hose. Before you do the latter, remove your O2 sensor and put a spark plug in it's place to plug the hole. PS, have fun getting that O2 sensor out w/out stripping it. Get yourself an O2 sensor wrench (not socket) and a thread chaser.
Now get your car tested, note which gas failed and refer to page one. Honestly I would be VERY surprised if you failed after this and if you did, there's not a whole lot else you can do. All you're left with is an intermittent fault ie coil, ignitor or the piston rings are shot and you need an engine swap
Here is a very basic rundown of smog failures and how you should address them on an OBD1 Honda. Essentially if you fail smog, you are not getting the most from your engine. Every effort should be made to pass smog legitimately because the end result is better performance, better fuel economy, better reliability, and less stress on the environment.
I am a certified I/M and Safety tech in the state of Utah where the ASM (dyno) test is required for OBD1 cars. I'm also very familiar with CA smog having lived there until recently.
Diagnosing an emissions issue requires looking at ALL of your gasses, not just the regulated gasses. Without analyzing CO2 and O2 readings, you cannot tell why the engine is running incorrectly.
CO Fail
High CO (above .1%) is caused by running rich. Besides failing smog, running rich reduces power and fuel economy, wears out your cat converter, and harms your O2 sensor. Running rich is commonly caused by a bad fuel pressure regulator (check vacuum and return line), aftermarket fpr, bad, clogged, or incorrect injectors for the application, bad O2 sensor, bad, missing, or tampered thermostat causing you to run cold, clogged air filter, chipped ECU, altered or tampered sensor wiring, etc.
HC Fail
There are two main causes of HC fails: air fuel ratio off, or weak ignition. %O2 and %CO will indicate a problem with air fuel ratio. %O2 above a couple % indicates you're running lean. If the idle speed is high, you have a vacuum leak. Check hoses and gaskets. If Idle is normal, check your fuel filter and O2 sensor. If %O2 is 0 and CO is high (.5 or higher), then you're running rich. Check your fpr, air filter, O2 sensor. Note that the O2 sensor can be weak and not throw a code. Remove it and clean it with a torch, wire brush, and compressed air. If it's old, just replace it.
If %O2 is near 0 and CO% is .0x or lower, then your problem is most likely a weak ignition system. Less commonly it could be low or uneven compression. Check your ignition rotor, distributor cap, spark plugs, ignition timing. Mist water over the spark plug wires with the engine running in the dark. If they're bad, you'll see sparks. If all these check out, get a multimeter and check the ignition coil and ignitor inside the distributor. If those are within spec, do a compression test. You can sometimes improve compression with a valve adjustment. Sometimes you have a burnt valve or worn piston rings.
Also make sure you are running the correct octane for the engine. SOHC Honda engines run best on 87 octane but have trouble burning 91. B Series VTEC motors have higher compression ratios and benefit from 91 octane.
NOx Fail
High NOx is caused by very hot combustion (1800-2500 F). Most Hondas do not have EGR (EGR cools the combustion chamber) except for Accords, the VTEC-E motors and 99 and later motors ie D17A, late D16Y8. When the EGR fails it most often is clogged on the intake side.
High coolant temps are often times the cause of high NOx for us. The gauge may indicate a normal temperature however I have found that it will give the same reading from 180-220 degrees F! A better indicator is that your radiator fan comes on often and stays on for a long period of time. An even better indicator is a pyrometer. Make sure the smog tech is using the dyno fan. Try flushing your coolant system at both the radiator and through the thermostat housing. One way to artificially increase the efficiency of your coolant system is to install a higher pressure radiator cap (stay within a few PSI of the stock rating). Just be aware that doing so will cause all your old hoses to blow. Silicon hoses are a very nice upgrade. Another option in non freezing climates is to run a slightly higher water concentration than the recommended 50/50 mix. Many people choose to run bigger and thicker radiators but this is usually overkill for non turbo applications.
JDM motors tend to have higher NOx emissions possibly due to their slightly higher compression. Retard the ignition timing to the low side of spec and run high octane. Seafoam the combustion chamber and make sure the coolant system is operating at its best. High NOx are also caused by lean mixtures (up to about 16.5:1 after which NOx levels tend to fall off). Check the O2 sensor, fuel filter, fuel pump strainer, and fuel pump.
NOx feeds back on itself meaning the NOx causes runaway NOx, often resulting in readings of 2000+. If your readings are this high it's a good indication that simply replacing the cat converter isn't going to be enough.
Catalytic Converter
Catalytic converters are the 2nd highest oversold item (meaning that good cat converters are often times replaced w/out cause). Repair shops love to replace catalytic converters because they are a high price item so there's a big margin. Often times a fresh cat converter will mask an engine problem and get you to pass smog, but the underlying problem will then destroy the cat converter so that you need to replace it again at your next smog check. Federal law requires that they are warrantied not to fail for at least 8 years or 80,000 miles (on a properly running engine). For this reason I recommend doing a complete tune-up and replacing the cat converter only as a last resort.
Catalytic converters should never wear out. Some things that kill cat converters or cause it not to work properly are 1) dropping it/scraping it, 2) running rich (overheats it and melts the precious metals inside) 3) Silicone (gives off a gas when hot which will temporarily coat the precious metals but will later burn off) 4) Phosphorus (from crappy oil or gas and from not changing the oil regularly).
Many times when your cat converter is not working efficiently you can remove it and blast the insides with a torch. It will give off some bright green and blue flames.
If your cat converter turns out to be bad, you can recycle it for about $20-30.
Properly Diagnosing the Cat Converter
The best way to test your cat converter is to first test your tail pipe emissions. Then drill a 3/16 hole in your exhaust pipe before the cat. Install the auxilliary adapter to the smog test probe and insert it in the hole. Measure the emissions and compare them to your previous reading. Comparing the pre and post cat readings will tell you its efficiency. OBD2 cars have an O2 sensor before an after the cat for this purpose.
O2 Sensor
O2 sensors greatly affect your AFR ratio because they are used for AFR feedback. A bad O2 sensor causing you to run rich will hurt your power in the driving range (WOT is unaffected unless you're in limp mode from a catastrophic O2 sensor failure). A bad O2 sensor causing you to run overly lean can cause additional stress on your engine. The most common symptom of a bad or lazy O2 sensor is hesitation, loss of power, and loss of fuel economy.
Note that under heavy load conditions (heavy and wide open throttle), O2 feedback is ignored and the ECU reads from a fuel table. This is why having your car dyno tuned can result in a significant power increase.
O2 Sensors are a maintenance part and will wear out and "get lazy" over time. Most times it will not cause a check engine light unless it's a catastrophic failure. You can test O2 sensors for laziness using a digital multimeter. The procedure can be found in the repair manual. Do not replace the O2 sensor w/out first verifying that it is bad. If your O2 sensor fails prematurely it's probably due to a blown headgasket (burning coolant), bad piston rings (burning oil), or running rich. Some types of engine cleaners and liquid gaskets can harm O2 sensors as well.
O2 and CO2 as Indicators
A good running engine will have low O2 (near zero) and high CO2 (near 14.9). There should be almost no O2 reading unless you have an air injected cat converter (S2000?). If you have a lot of O2, you're running lean. O2 can sometimes be caused by an exhaust leak.
Full Tune-Up
Besides the regular tune up items (distributor cap, rotor, spark plugs, synthetic oil change, base ignition timing, tire pressure, air filter, PCV) you should also perform the following according to the maintenance schedule: fuel filter, fuel pump strainer (inside fuel tank), have your injectors balanced/blueprinted (especially on JDM imports), remove and clean out your throttle body, IACV, and intake manifold. Adjust the slack in the throttle cable and a/t cable. Seafoam the motor a few dozen miles before you change the oil and filter spark plugs and O2 sensor if applicable. Check plug wires. Test O2 sensor with a multimeter. Some states have begun testing charcoal canisters. Your fuel cap may need to be replaced if it fails the test.
Effect on the Environment
NOx
Oxides of Nitrogen cause a nasty haze above cities that carries over into many famous wilderness areas ie the Grand Canyon. It combines with industrial emissions and hydrocarbons from cars to cause acid rain. It causes eutrophication which kills fish and degrades water quality. It creates particulate matter small enough to bypass the tiny hair follicles in your throat and embed directly into your lung tissue causing cancer. Most NOx emissions come from power plants and diesel engines.
CO2
Carbon Dioxide is a greenhouse gas and a cause of climate change. Plants convert CO2 into sugar and O2 but cannot keep up with the amount we are generating. An effort needs to be made to limit the amount of CO2 emitted in the atmosphere so that the plants and plankton in the ocean can handle it so the world is still livable for puppies and children.
CO
Carbon Monoxide is clear, odorless, and poisonous. It gets into your blood displacing the oxygen and stays there until the blood cells die. Over time, CO accumulates in your system causing you to be forgetful, feel lazy, and have headaches. It also contributes to global warming.
Interestingly, the most effective regulation to reduce air pollution has been the requirement to test gas caps. A bad gas cap will cause many times as much pollution as a car that failed on HC's. The worst part about a bad gas cap is that the car doesn't even have to be running to emit pollution.
2014 edit (taken from page 4)
So for background info I posted this thread in 2008 and haven't worked in safety/emissions in over 4 years. Honestly, when I have an emissions problem I'll often reference this thread, as I often reference some of my other threads on other sites for other info and of course my own damn website I never imagined I would still be messing with Hondas and answering questions on forums 6 years later (got into the game in 2002 actually) but I just bought another VX winter 2013 and this is a great little community so here goes:
EVERYONE IN THIS THREAD SHOULD READ THIS
These cars are all over 20 years old and in the hundreds of thousands of miles. A simple tune up (oil, spark plugs, rotor, cap, PCV, check wires, ignition timing, fuel filter, check O2 sensor, check idle speed) just doesn't cut it anymore. If you haven't even gotten this far, put away your smart phone and come back when you have.
(On your VX make sure you have the right spark plugs in there and only use NGK or dealer plugs. Most VXs have the wrong ones since the application is often incorrect and most parts stores stopped carrying the correct plugs (try amazon).)
After the basics, you still need to do some reconditioning before you can even get a baseline for diagnosis.
All VX's and most other models need the intake manifold removed and thoroughly cleaned, especially around the EGR ports. Remove the MAP sensor as it is sensitive to cleaners and solvents. You'll need a new throttle body gasket and intake manifold gasket and you can't count on the bigger auto parts chain stores having them anymore. Oven cleaner works reasonably well for cleaning baked on gunk, but it will still require a lot of soaking and brushing. Aircraft remover helps get the old gasket off along with a razorblade scraper and a fine grit sand paper on a grinder. Also clean the head ports and injector holes a bit but don't get a bunch of gunk into the cylinders and don't spray too much throttle body cleaner in there or you'll have a fun time drying it out so it can start again. While you have the manifold off, pull the breather box off, clean it out and replace the O ring to the block. You'll need the exact right size O ring.
All EGs need fuel injector service. I like Injector Rehab. VXs and CXs have smaller injectors than all other D and B series (which are all 240CC) so keep this in mind if you plan to send junkyard injectors in to minimize downtime.
All EGs need valve adjustments (see my other thread). You will find that each valve is inconsistent with the next and that the intake side is often too tight and the exhaust side too loose. This is wasted power potential, wasted gas, preventable emissions, premature death for your O2 sensor and cat converter, and it's hard on your engine because some cylinders are running rich and others lean.
Put 1/3rd can of Seafoam in the fuel tank, oil, and suck the other 1/3rd in the brake hose. Before you do the latter, remove your O2 sensor and put a spark plug in it's place to plug the hole. PS, have fun getting that O2 sensor out w/out stripping it. Get yourself an O2 sensor wrench (not socket) and a thread chaser.
Now get your car tested, note which gas failed and refer to page one. Honestly I would be VERY surprised if you failed after this and if you did, there's not a whole lot else you can do. All you're left with is an intermittent fault ie coil, ignitor or the piston rings are shot and you need an engine swap
Last edited by suspendedHatch on Thu Oct 09, 2014 5:41 pm, edited 6 times in total.