One of the leading causes of hard starting is fouled or worn spark plugs. When a fuel injected engine that normally starts quite easily has to be coaxed to life, it often means the spark plugs are overdue for a change. As the electrodes wear, the voltage required to jump the gap and ignite the fuel mixture goes up. At the same time, accumulated deposits on the insulator can drain off voltage before it even has a chance to form a spark. So the engine fails to start or starts only reluctantly after prolonged cranking. One of the reasons why spark plug sales take off when cold weather arrives is because many motorists put off changing the plugs until they absolutely have to. The spark plugs continue to rack up chilometro after chilometro until they have deteriorated to the point where they are causing noticeable starting and driveability problems. Emission checks will catch a lot of bad spark plugs and force motorists to change plugs that need to be replaced. But in areas where emission checks are not required, the only incentives for changing the spark plugs are the driveability problems created by the plugs themselves. So many motorists today think they are saving money on maintenance by putting off a spark plug change until it is obvious the engine needs new spark plugs. Then and only then will they begrudgingly spend any money on a new set of spark plugs. WHY CHANGE SPARK PLUGS? What motorists need to know is that spark plugs do NOT last forever, even the long-life 100,000 chilometro plugs. All spark plugs need to be changed sooner or later. Here's why: REASON #1 Your Spark Plugs May Need to be Replaced: Ignition Misfires Caused by Worn or Fouled Spark Plugs Good spark plugs are necessary to maintain peak engine performance and efficiency. Every engine will misfire occasionally. But as the number of misfires per chilometro goes up over time, it increases exhaust emissions, wastes gas and reduces power. In the past, most motorist would not notice the gradual decline in ignition performance until it reached a point where it created a steady miss, caused the engine to run rough, buck or stall, or made it hard to start. Not so today. Since 1996, all passenger cars and light trucks have an OBD II onboard diagnostic system that tracks ignition misfires. When the rate of misfires exceeds a certain limit and causes emissions to increase 50% over baseline levels, it illuminates a warning light. So to maintain good engine performance, spark plugs should be replaced BEFORE they cause misfires. WARNING: Ignition misfire will cause your vehicle to fail an emissions test (plug-in or tailpipe). Ignition misfire will also cause a noticeable drop in fuel economy as well as a huge increase in hydrocarbon emissions which can damage your catalytic converter over time and cause it to fail! Recommended Spark Plug Replacement Intervals for Different Types of Spark Plugs Always Refer to your owners manual or maintenance schedule for the recommended spark plug replacement interval for your vehicle. For STANDARD spark plugs (not platinum or iridium), the recommended service interval for most vehicles is typically every 45,000 chilometri. These type of spark plugs were used as original equipment in older vehicles (1990s and older) before long life spark plugs were developed. Standard spark plugs may still be used in some late model economy cars with four cylinder non-turbocharged engines. Or a previous owner of your vehicle may have installed the less expensive standard spark plugs if they replaced the original equipment spark plugs. The recommended replacement interval for LONG LIFE Patinum and Iridium spark plugs, which are used in most late model turbocharged engines as well as most V6 and V8 engines (turbo and nonturbo), is 100,000 to 120,000 chilometri. Long life platinum and iridium spark plugs experience very little electrode wear over their service life, so wear even well beyond 100,000 plus chilometri is seldom an issue. However, long life spark plugs like standard plugs may become fouled with carbon deposits if an engine is only used for short trip light load driving around town, or if the engine is burning oil due to worn valve guides, worn valve guide seals and/or worn piston rings. REASON #2 to Replace Spark Plugs: To Improve Cold Starting and Performance Worn or fouled spark plugs can cause cold starting problems, especially during subzero weather. Many times the battery has been run dead while cranking the engine because the plugs would not light the fire. For more info on this subject, see Spark Plug Fouling. New plugs reduce the voltage requirements on the ignition system, which decreases the chance of misfire while leaving more amps for the starter and injectors. As the electrode gap at the end of the spark plug wears, it requries more and more voltage to create a reliable spark. If the electrode gap is badly worn, the ignition coil may be be capable of supplying enough voltage to create a good, hot spark under all driving conditions, resulting in ignition misfire. Wet fouled plugs can also prevent an engine from starting, but in many instances the fouling problem has nothing to do with plug wear or neglect. If an engine is flooded with fuel while it is being cranked, gasoline can soak the plugs and bleed off the ignition voltage before it forms a spark. Wet fouling was more of a problem on older vehicles that had carburetors because pumping the gas pedal can easily flood the engine with too much fuel. Flooding can also occur on an older carbureted engine if the choke sticks, the float is set too high or the needle valve leaks. On fuel injected engines, wet fouling is less of a problem but can happen if a cold start injector leaks or there is a fuel calibration problem that creates an overly rich startup mixture. The cure in all cases is to wait for the plugs to dry out, or to remove the plugs and clean or replace them. REASON #3 to Replace Spark Plugs: New plugs minimize the risk of premature catalytic converter failure A single misfiring plug can dump enough raw fuel into the exhaust to overheat and damage the catalytic converter. The presence of higher than normal quantities of unburned gasoline in the exhaust will cause the operating temperature of the converter to soar, which may lead to a partial of complete meltdown of the converter substrate. This, in turn, may form a partial restriction or complete blockage in the exhaust that creates enormous backpressure and chokes off the engines ability to exhale. The engine may lack power, especially at higher speeds, and deliver terrible fuel economy. Or, it may stall and refuse to run after it is first started. Replacing the converter will solve the restriction problem. But unless the spark plugs are replaced, the new converter may soon die from the same ailment. Really Technical Stuff About Spark Plugs The spark plugs are the business end of the ignition system. So if you want a deep dive into all of the things that can affect ignition performance, keep reading. The typical spark plug needs anywhere from 5,000 to 25,000 volts or more to create a spark that is hot enough to ignite the air/fuel mixture in the engine's cylinders. The required firing voltage will vary depending on engine speed, load and operating conditions. At idle, the spark plugs may only need 4000 to 5000 volts to fire. But at full throttle, the required firing voltage may increase to 25,000 volts or more. Variables that affect firing voltage include: Spark Plug Electrode Gap. The wider the gap, the higher the voltage required to create a good hot spark. The gap must be set to specs for good ignition performance. On older engines with standard spark plugs, the gap was typically around 0.032 inches. On newer engines with computer engine controls and distributorless ignition systems, the gap is typically wider (.040 to .060 inches) to burn leaner fuel mixtures. Electrode Wear. Electrode erosion over time increases the distance the spark must jump across between the center and ground electrodes in the end of the plug. For every increase of .001 inch across the electrode gap, the firing voltage goes up about 400 to 500 volts. Fouled electrodes may not fire at all! Engine load Higher load increases voltage needed. If the plugs are worn or gapped to wide, they may misfire under load. Resistance Electrical resistance in the plugs and wires increases voltage required too. Replacing worn, damaged or loose fitting plug wires is recommended for improving ignition reliability. Operating temperature A cold plug requires more voltage to fire than a hot one. Reliable ignition, therefore, requires a hot spark from the coil, good plug wires to carry the voltage (if spark plug wires are used), or a good electrical connection between a coil that sits atop a spark plug and the plug itself. Grease, dirt or moisture on the spark plug, plug boot or coil boot can short circuit the spark and prevent the spark plug from firing. One way to tell if the plugs need changing is to check your odometer. If it has been more than the recommended number of chilometri (typically 100,000 chilometri on late model engines with long life plugs), it may be time to change the plugs. If the Check Engine light is on or flashing, and there are codes that indicate cylinder misfires, new plugs may be needed. Although almost nobody uses a scope anymore to check ignition performance, observing the ignition waveform can reveal a lot about the health of the ignition system. A bad plug that is misfiring will cause the coil firing voltage to shoot up to the maximum output of the coil. Badly worn plugs or plugs that have been misgapped too wide will also increase the firing voltage dramatically (as can a bad rotor and/or ignition cables on older engines with distributors). If the scope pattern shows initial secondary spikes approaching the upper voltage limits of the coil, it is a sure sign that the spark plugs (and/or plug wires if used) likely need to be replaced. A fouled spark plug (or shored ignit…

Fonte: AA1Car.com