Emissions testing or Smog testing is used in many areas of the country to improve air quality. But even if your community is not affected, you still need to know about emissions testing and smog checks because problems that often cause emission failures can also cause a variety of driveability and performance complaints. Mandatory emissions testing has become a fact of life in many areas as a means of identifying vehicles that are "gross polluters" so they can be fixed. See States That Require Vehicle Emissions Testing to see if your state requires emissions testing. Such programs force vehicle owners to have emission problems repaired that might otherwise be ignored. So when a vehicle fails an emissions test or a smog check, most motorists are not exactly overjoyed to learn that repairs are needed. Everybody is for clean air as long as somebody else pays for it. That is why all new cars and light trucks built from 1981 through 1995 have had a 5 year, 50,000 chilometro federal emissions warranty. This warranty covered all emission control components as well as the fuel delivery system (except the pump and filter), ignition system (except spark plugs), and engine management system including all sensors. In 1995, the federal emissions warranty requirements changed. The warranty was extended to 8 years and 80,000 chilometri on the powertrain control module and catalytic converter, but rolled back to only 2 years and 24,000 chilometri on everything else. Even so, all of these components are still covered for 3 years or 36,000 chilometri (or longer) by the individual vehicle manufacturers bumper-to-bumper warranties. In California, the coverage is much longer. Once a vehicle is out of warranty, the burden of paying for emission repairs becomes the sole responsibility of the vehicle owner. Most inspection programs include "waiver" provisions that limit the amount of money motorists have to spend on emission repairs. If an emissions problem cannot be resolved within the specified waiver limit (which may be anywhere from $50 up to $450 depending on the local regulations and applicable model year), the vehicle gets a "pass" even though it may still be a polluter. The objective, therefore, is to get the most bang for your repair buck (the most pollution reduction for the least out-of-pocket repair expense). When a vehicle has multiple problems (one or more fouled or worn spark plugs, one or more bad plug wires, plus worn rings and valve guides), zero in on the repairs that will make the most noticeable improvement. A single misfiring plug, for example, can increase hydrocarbon emissions enormously (10 times normal!). Replacing the spark plugs (and plug wires if necessary) will eliminate the misfire problem (at least temporarily) and make a dramatic difference in reducing the engines overall emissions. The vehicle may still not be in compliance because the engine is burning oil, but it will run cleaner than it did before and have cost far less than an engine overhaul. EMISSIONS TESTING: WHAT THEY CHECK Each state or municipality determines its own cut points for emissions testing as well as the specific tests that must be performed. Most test programs look at only two pollutants: unburned hydrocarbons (HC) and carbon monoxide (CO). Most also measure carbon dioxide (CO2) but only for diagnostic purposes since CO2 is not a pollutant (though it is a "greenhouse gas" that may contribute to global warming). Although most emission test programs have now gone to a simple OBD II plug-in test (which does NOT measure tailpipe emissions but checks your vehicle computer for any faults that might increase emissions), some inspection programs may require visual checks of various emissions-related equipment for evidence of tampering. These include: Checking the restrictor in the fuel tank filler neck to make sure it has not been knocked out or enlarged to accept regular leaded gasoline. Inspecting the gas cap to make sure it is the correct type for the application and seals tight. Looking under the car to see that the catalytic converter is in place. Checking the instrument panel to see if the "Check Engine" or malfunction indicator lamp is illuminated. Checking under the hood to make sure the engine has all the required emission control components (California primarily). Checking any nonstock aftermarket parts on the engine to make sure they are emissions certified (California primarily). If an engine has been swapped or replaced, making sure it has all the required emissions equipment for the original model year and application (California primarily). In areas that do an I/M 240 test, they check oxides of nitrogen (NOX) emissions as well as total emissions in grams per chilometro as the vehicle is run at various speeds and loads on a dyno. An I/M 240 test may also require checking the integrity of the fuel system for air leaks (evaporative emissions) and the flow capacity of charcoal canister purge valve. In areas that do an OBD II plug-in emissions check, they want to make sure the Check Engine light is functioning and is OFF, and that there are no trouble codes present. AUTOMOTIVE EMISSIONS TEST STANDARDS The cut points for acceptable HC and CO levels are generally based on the emission standards that a vehicle was required to meet when it was new, so older vehicles have more lenient emission standards than new ones (see chart). EMISSIONS CUT POINT CHART Model year…Typical Cut Points…Well-tuned engine …………..CO%…..HC ppm……….CO%…..HC ppm pre-1968….. 7.5-12.5… 750-2000….. 2.0-3.0… 250-500 1969-70….. 7.0-11.0… 650-1250….. 1.5-2.5… 200-300 1971-74….. 5.0-9.0… 425-1200….. 1.0-1.5… 100-200 1975-79….. 3.0-6.5… 300-650….. 0.5-1.0… 50-100 1980…….. 1.5-3.5… 275-600….. 0.3-1.0… 50-100 1981-93….. 1.0-2.5… 200-300….. 0.0-0.5… 10-50 1994 & up….. 1.0-1.5… 50-100….. 0.0-0.2… 02-20 Notice in the emissions cut point chart that the actual emissions produced by the average well-tuned engine are substantially less than the cut points required to pass an emissions test. The actual cut points are more lenient because the goal of emissions testing is to identify the gross polluters so they can be fixed and brought back into compliance. WHAT HAPPENS IF YOUR VEHICLE FAILS AN EMISSIONS TEST When a vehicle fails an emissions test, the motorist usually receives a printout that show the test results of the vehicles emissions as well as the applicable cut points. From this, you can determine if too much HC and/or CO caused the vehicle to fail. Hydrocarbon failures mean unburned gasoline is passing through the engine and entering the exhaust. The three most common causes include ignition misfire, lean misfire and low compression (typically a burned exhaust valve). Ignition misfire can be caused by worn or fouled spark plugs, bad plug wires or a weak coil. Lean misfire results where there is too much air and not enough fuel, so check for vacuum leaks, dirty injectors or a fuel delivery problem. In addition to these, hydrocarbon failures can also be caused by oil burning due to worn valve guides, valve guide seals and/or rings. Carbon monoxide failures indicate an overly rich fuel mixture. On older carbureted engines without electronic feedback controls, look for things like a stuck choke, misadjusted or fuel saturated float or a rich idle mixture adjustment. On newer vehicles with electronic carburetors or fuel injection, the system may not be going into closed loop because of a bad coolant or oxygen sensor. If both HC and CO are high, the vehicle may have a bad catalytic converter or an air pump problem. For more info on catalytic converters, Click Here for Troubleshooting a P0420 Catalyst Code NOX failures are usually EGR-related, since the EGR system is primarily responsible for reducing oxides of nitrogen. But NOX emissions can also be caused by a bad three-way converter or a computer control system that remains in open loop. EMISSIONS PERFORMANCE CHECKS There are five things you should always check on every vehicle that has a computerized engine control system: 1. Scan for fault codes. Any codes that are found need to be dealt with before anything else. 2. Make sure the system is going into closed loop. No change in loop status often indicates a coolant sensor problem. 3. Confirm that the system is alternating the fuel mixture between rich and lean. This is absolutely essential for the converter to function efficiently. You can do this by observing the O2 sensors output with a scan tool, or directly with a digital storage oscilloscope or voltmeter. If everything is okay, the sensor should be producing an oscillating voltage that flip-flops from near minimum (0.1 to 0.2v) to near maximum (0.8 to 0.9v). O2 sensors in feedback carburetor applications have the slowest flip-flop rate (about once per second at 2500 rpm), those in throttle body injection systems are somewhat faster (2 to 3 times per second at 2500 rpm), while multiport injected applications are the fastest (5 to 7 times per second at 2500 rpm). 4. Confirm that the system responds normally to changes in the air/fuel mixture. To test the system response, pull off a vacuum hose to create an air leak (not too large or the engine will die). You should see an immediate voltage drop in the O2 sensor output, and a corresponding increase in injector dwell or mixture control dwell from the computer. Making the fuel mixture artificially rich by injecting some propane into the intake manifold should cause the O2 sensor output to rise and the computer to lean out the fuel mixture. 5. Use your scan tool to confirm all monitors have completed and that the vehicle is ready for emissions testing BEFORE it goes to a test station. If all monitors are ready, and no faults have been found, the vehicle should pass an OBD II plug-in emissions test. READING EMISSIONS: EXHAUST GAS ANALYSIS Though a good technician can often diagnose and repair emission problems without ha…

Fonte: AA1Car.com