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Exhaust and Emissions

Ticking Exhaust Sound

Q: When I accelerate I hear a ticking sound. I think it may be an exhaust leak.

A: You could have an exhaust manifold gasket that is failing. Have it checked out by a qualified technician. If your exhaust is leaking you could be getting Carbon Monoxide inside the car. Carbon Monoxide is an odorless, deadly gas so get it checked out right away.

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Failed Emissions Test - High NOx

Q: My car failed the emission testing at the inspection station. The inspector said the engine exceeded the acceptable oxides of nitrogen. What could cause these high levels?

A: High NOx (oxides of nitrogen) levels can be caused by incorrect ignition timing (common cause on older vehicles), faulty EGR (Exhaust Gas Recirculation) system, engine running lean (air-fuel ratio), engine overheating, carbon deposit buildup in the combustion chambers, or a defective catalytic converter.

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Air Pump

Q: Is it ok for me to remove the air pump on my 1986 motor home? I was told that it might increase my gas mileage.

A: The air pump is part of your emission control system. This system is designed to reduce pollution outputs on your vehicle. It is illegal to tamper with or remove any part of the emissions system.

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Carbon Monoxide

Q: I was driving yesterday and for no apparent reason I almost fell asleep. I have never done that. I was wondering if the car emits carbon monoxide as I drive it?

A: Carbon monoxide, a pollutant, is released from incomplete combustion in internal combustion engines. If there is a leak in the exhaust system you could be getting this odorless, colorless, and poisonous gas in the vehicle. Symptoms include headaches, shortness of breath, dizziness, fatigue, nausea, and confusion. I would get the vehicle inspected by a qualified technician right away. In the meantime, keep plenty of air moving through the car by keeping the windows open.

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Catalytic Converter

Q: What could be causing a rotten egg smell to come out of my car’s tailpipe?

A: The smell is from a sulfur buildup in the catalytic converter. The converter or other emission system component may be faulty. If the check engine light has come on, a diagnostic code is triggered and stored in the car’s computer. A service technician can retrieve the code with a scan tool. Sometimes you can get a tank of gas that has a high sulfur content. Try filling up with a different brand of gasoline. If this doesn’t work, a repair facility may be able to diagnose the problem further by using an exhaust gas analyzer.

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Catalytic Converter Clogged

Q: What causes a catalytic converter to fail?

A: A rich fuel mixture can cause the catalytic converter to prematurely fail. If unburned fuel enters the converter, it can overheat. The exhaust gases can be analyzed to determine if the air/fuel mixture is correct. An overuse of some fuel additives can also shorten the converter’s life. A loss of power, poor fuel economy, or engine missing can be signs of a clogged converter. A catalytic converter often lasts the lifetime of the vehicle. But if you are having a problem, be sure to check your owner’s manual for the emissions system warranty. Often this warranty exceeds the car’s normal warranty.

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Catalytic Converter Cut Off

Q: Will it cause problems with my car if I cut off the catalytic converter and put a straight pipe in its place?

A: Cars are designed to run properly with the catalytic converter. Do not cut it off. It is illegal to remove a catalytic converter. Without a catalytic converter your vehicle will emit large amounts of pollution and will not pass emission tests.

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EGR Valve

Q: My truck set a code several months ago for the EGR valve. At that time I really wasn't noticing any problems. Since then, the truck has started jerking or bucking around 45 or 50 MPH. If you accelerate the problem seems to go away. It also has a roaring sound, when you let off the gas and coast down to make a stop. You can here the roaring sound when the car is idling but as soon as you press the accelerator the sound goes away or gets really faint. What is the purpose of the EGR valve?

A: The purpose of the EGR (Exhaust Gas Recirculation) valve is to lower the oxides of nitrogen (N0x). It controls the quantity of exhaust being directed back into the intake manifold, actually to cool the combustion process. An EGR valve that is not functioning properly can cause jerking, hesitation, or rough idling.

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Hole in Muffler

Q: Is driving a car with a hole in the muffler dangerous?

A: A hole in the muffler may allow exhaust gases to enter the car’s passenger cabin. Carbon monoxide, a toxic substance in exhaust, comes from the burning of fossil fuels (e.g., gasoline and diesel) and is colorless, tasteless, and odorless. It is a very dangerous and deadly gas. When inhaled, carbon monoxide enters the bloodstream. Once in the bloodstream, carbon monoxide displaces oxygen and thereby reduces the body’s ability to absorb and transport oxygen to vital organs. I would recommend replacing the muffler to minimize the chance of breathing in these fumes.

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Muffler Dripping Water

Q: What would cause water to drip from the back of my car’s muffler?

A: Auto manufacturers commonly put a “weep” hole on the rear, bottom part of the muffler. This allows water to exit, reducing inside corrosion. Water is a normal tailpipe emission created by the catalytic converter. The catalytic converter reduces harmful gases that come from the engine (e.g., carbon monoxide, hydrocarbons, and nitrogen oxides) and changes them into water, carbon dioxide, and nitrogen gas. The water that is dripping from your tailpipe is from this process and from condensation inside the exhaust system.

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Muffler Louder

Q: My car is louder than it was a couple of years ago, but I don’t see any visible holes in the exhaust system. What might be the problem?

A: Inside most mufflers are baffles. The baffles help reduce noise. Since mufflers rust from the inside out, it is most likely that your muffler is worn out. When replacing the muffler, you may also consider replacing the intermediate pipe (the pipe between the muffler and the catalytic converter) and the tailpipe. Replacing all of these components at once makes installation much easier as compared to only replacing the muffler.

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Muffler Replacement

Q: How often do I need to change the muffler on my car?

A: Mufflers are not on a scheduled maintenance interval like oil changes. They often last 100,000 miles or so, but this depends on the specific vehicle and driving conditions. Inspect the muffler for rust holes or lightly tap on the bottom of the muffler with a hammer. If you hear debris/rust bouncing around inside the muffler it is time for replacement.

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Oil in the Air Filter Housing

Q: What may be causing oil to collect in the air cleaner housing on my car?

A: The most common suspect is the PCV valve. PCV stands for Positive Crankcase Ventilation. This little component is responsible for keeping crankcase pressure in check and recycling unburned fuel. An important component in the emissions system, the PCV valve reroutes any unburned fumes from the crankcase caused by blow-by to the intake manifold. Once in the intake, the fumes are eventually combined with the air/fuel mixture in the combustion chamber and then burned. This process minimizes hydrocarbons and other gases that are released into the atmosphere. The PCV valve is usually inserted in or near the valve cover.

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Oxygen Sensors

Q: When I was inspecting the exhaust system I noticed a small component with a wire going to it. What is this part?

A: What you are referring to is an oxygen (O2) sensor. In many vehicles there is an O2 sensor before and after the catalytic converter. Cars with two catalytic converters can have four O2 sensors. The O2 sensor monitors the exhaust gases and measures the oxygen content in the gases. It continuously reports the results to the car’s electronic control unit to maintain the most efficient air-fuel ratio. A faulty O2 sensor can cause the car to receive poor fuel economy, increased emissions, poor acceleration, rough idle, premature failure of the catalytic converter, and more.

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Oxygen Sensor Replacement Intervals

Q: Is it common to replace Oxygen sensors as a normal tune-up item? What do they cost?

A: Oxygen (O2) sensors should be replaced as a preventative maintenance item. Check your owner’s manual for the specific maintenance timeline. In general, O2 sensors should be replaced between 30,000-100,000 miles depending on the style of sensor and vehicle type. Your vehicle could have as many as four O2 sensors. A correctly functioning O2 sensor could increase fuel economy as much as 10-15% over one that is not working properly. O2 sensors typically cost between $50-$100 each.

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Q: What causes smog?

A: Smog (photochemical smog) is a type of air pollution. The word smog originally came from the two words smoke and fog. Photochemical smog forms from hydrocarbons, nitrogen oxides, and sunlight. Automobiles and other fossil fuel burning engines contribute to photochemical smog by emitting hydrocarbons and nitrogen oxides into the air.

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Warming Up an Engine

Q: How long should I warm up an engine?

A: This depends on how cold it is outside, but generally about 15 - 30 seconds is sufficient to get the oil circulating. After that, you are wasting fuel and adding pollutants to the air. Many states have anti-idling laws. In addition, you shouldn't leave your vehicle unattended when it is idling. After 30 seconds or so, accelerate slowly. Driving the vehicle in a moderate way is the best way to warm it up. The only rationale to idle longer would be to clear the windows for visibility if you couldn't get them clear with an ice scraper.

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