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It?s not just hot air?it?s keeping your car healthy

by Bengt Halvorson

Don't wait until the check engine light goes on, or you fail a tailpipe test required by the DMV. Even if you're good about oil and filter changes, regular maintenance, and keeping your car in good mechanical shape, a malfunctioning or ineffective emissions system could be choking your engine and affecting performance. Especially if your car is more than three years old, paying some regular attention to the emissions system can assure you that your vehicle is operating at its peak, and it will save you money in the long run.

Here's a quick rundown of the common components of an emissions system, and what happens to them with age:

PCV Valve: The most rudimentary emissions device, the PCV (positive crankcase ventilation) valve siphons excess gases that build up in the crankcase and routes them back into the intake manifold, assuring that the gases only flow in that direction. Those gases that build up in the crankcase tend to contain unburned fuel fumes, so the PCV valve plays a big, but simple part in cleaning up emissions. PCV valves have an internal spring, and they simply either become clogged or wear out over time. They're inexpensive and quite easy to replace on most cars.

Catalytic converter: The purpose of the catalytic converter is to burn unburned hydrocarbons in the exhaust. The catalytic converter is lined with special reactive chemicals that are depleted over time, so just because one looks intact and hasn't rusted through doesn't mean it shouldn't be replaced. If you smell unburned fuel even when the engine is warmed up, and otherwise your engine is running smoothly and efficiently, then the cat is the prime suspect. Due to the fact that the reactive chemicals (the catalysts) deplete over time, catalytic converters have a limited life. Catalytic converters are usually the most expensive emissions component to replace, so pay attention to other minor problems that might reduce the cat's life.

Oxygen sensor: Oxygen sensors are perhaps the most important component in a modern vehicle emissions system. They use the oxygen content of the hot exhaust gas to see how cleanly the engine is burning. If there is too much oxygen, there is likely also too high a level of unburned hydrocarbons. Oxygen sensors have a limited service life, and they should be replaced at least once every five years, or as often as your owner's manual recommends. An improperly operating oxygen sensor can cause the engine computer to run on an abnormally rich fuel/air mixture, which could lead over time to significantly shorter catalytic converter life.

Air pump: Many vehicles utilize an air pump that adds air at or near the exhaust manifold, or just before the catalytic converter. The added oxygen helps combust unburned gas in the exhaust, and it also aids in the operation of the cat.

EGR valve: The exhaust gas recirculation valve allows some exhaust gas to be rerouted back into the engine's combustion chambers, to keep combustion cool enough to avoid excess nitrous oxide creation.

Exhaust seals: If leaky, these can reduce the back pressure in your exhaust system and interfere with the proper operation of the catalytic converter. If a seal is leaky, your engine might start to sound slightly different or idle roughly, but sometimes it takes a mechanic's leak test to spot the problem.

Vacuum hoses: These hoses serve varied purposes, depending on the design of the emissions system, but they generally have a part in keeping (intake) manifold vacuum constant, and in doing so combustion conditions stay at their peak. Hoses in general become brittle and cracked with age, and these small ones are no exception. They should be inspected and replaced before they lose their flexibility.

Fuel injectors: Modern fuel injectors are, in a way, emissions devices because they spray and measure fuel for the cleanest, most efficient burn possible. If fuel injector nozzles are slightly clogged and not spraying in the correct pattern, emissions can be affected while otherwise performance might seem normal.

Muffler: It might be a surprise that the muffler is an important component of the emissions system. Although their obvious purpose is to quiet the noise of combustion, mufflers also moderate pressure, assuring that there is enough back pressure for the engine to operate at its intended efficiency and for the catalytic converter to operate at the right temperatures to combust unburned gasoline.

Emissions 'bag tests,' the most common type of auto emissions test, simply measure the concentration of several different harmful gases (like carbon dioxide, carbon monoxide, hydrocarbons, nitrogen oxides, and others) based on an analysis of what comes out the tailpipe. This is matched to the quantity range of pollutants that is considered normal for your car, and based on that the car is either passed or failed.

Remember that all the components in the emissions system operate together as a system, and that by neglecting a seemingly insignificant one, you might be reducing the life of your expensive catalytic converter and increasing engine wear. Admittedly, there was a time when emissions components were haphazardly added to old-design, free-breathing engines, but today's emissions systems are designed from the start as an important part. Operating your vehicle with any of these components not properly working will be detrimental to performance and the life of your engine. Your vehicle's emissions system is only as strong as its weakest link.