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What can a dirty air filter can cause ?

A dirty air filter can cause excessive gas consumption. For efficient operation, an engine needs about 15 parts of air for every part of gas (by weight). When the air filter is so clogged with dust and dirt, bugs and debris that the air is choked off, the fuel/air mixture becomes too "rich" (too much gas). The engine will perform poorly and exhaust emissions will increase. Gas mileage will decrease.

If the condition is not corrected, the spark plugs will become fouled, leading to possible damage to the catalytic converter. Bottom line: a clean air filter is cheap car care insurance.

What is a remedy for an engine that is hard to start on a damp morning ?

Drying off the spark plug wiring is a remedy for an engine that is hard to start on a damp morning. Moisture, a conductor of electrical current, can do weird things to electrical and ignition systems. Among other things, it can short out one or more spark plugs since it diverts current flow.

What could a bad spark plug cause?

A bad spark plug could ruin the catalytic converter or cause erratic shifting of the automatic transmission. A misfiring spark plug could cause the destruction of the catalytic converter because of the unburned fuel it would add to the exhaust. The converter, located in the exhaust system, becomes extremely hot in the process of converting unburned hydrocarbons (gasoline) to harmless water and carbon dioxide. Feed enough fuel into this little furnace and it will self-destruct.

As for erratic transmission shifting, the engine and transmission work as a team. When the engine tells the transmission it's struggling, as it would with one spark plug out of business, the transmission shifts up and down trying to compensate for the disability. The symptom often is mis-diagnosed as transmission problems when the real culprit is nothing more than a misfiring spark plug.

What can a leaking vacuum hose on the EGR (exhaust gas recirculation) valve can cause an engine to do ?

A leaking vacuum hose on the EGR (exhaust gas recirculation) valve can cause an engine to idle rough. The EGR (exhaust gas recirculation) system, which reduces emissions by admitting small amounts of exhaust gas into the intake manifold, is controlled by engine vacuum. A leaking or clogged vacuum hose or other malfunction of this valve can cause poor engine performance and high exhaust emissions.

Any discrepancy in this system normally would be detected in a diagnostic engine check.

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General Car Tip Questions
What can a dirty air filter can cause ? A dirty air filter can cause excessive gas consumption. For efficient operation, an engine needs about 15 parts of air for every part of gas (by weight). When the air filter is so clogged with dust and dirt, bugs and debris that the air is choked off, the fuel/air mixture becomes too "rich" (too much gas). The engine will perform poorly and exhaust emissions will increase. Gas mileage will decrease. If the condition is not corrected, the spark plugs will become fouled, leading to possible damage to the catalytic converter. Bottom line: a clean air filter is cheap car care insurance. What is a remedy for an engine that is hard to start on a damp morning ? Drying off the spark plug wiring is a remedy for an engine that is hard to start on a damp morning. Moisture, a conductor of electrical current, can do weird things to electrical and ignition systems. Among other things, it can short out one or more spark plugs since it diverts current flow. What could a bad spark plug cause? A bad spark plug could ruin the catalytic converter or cause erratic shifting of the automatic transmission. A misfiring spark plug could cause the destruction of the catalytic converter because of the unburned fuel it would add to the exhaust. The converter, located in the exhaust system, becomes extremely hot in the process of converting unburned hydrocarbons (gasoline) to harmless water and carbon dioxide. Feed enough fuel into this little furnace and it will self-destruct. As for erratic transmission shifting, the engine and transmission work as a team. When the engine tells the transmission it's struggling, as it would with one spark plug out of business, the transmission shifts up and down trying to compensate for the disability. The symptom often is mis-diagnosed as transmission problems when the real culprit is nothing more than a misfiring spark plug. What can a leaking vacuum hose on the EGR (exhaust gas recirculation) valve can cause an engine to do ? A leaking vacuum hose on the EGR (exhaust gas recirculation) valve can cause an engine to idle rough. The EGR (exhaust gas recirculation) system, which reduces emissions by admitting small amounts of exhaust gas into the intake manifold, is controlled by engine vacuum. A leaking or clogged vacuum hose or other malfunction of this valve can cause poor engine performance and high exhaust emissions. Any discrepancy in this system normally would be detected in a diagnostic engine check.