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There are many things that can cause a single-cylinder misfire. This could be a faulty spark plug, plug wire, ignition coil, fuel injector, intake leak around cylinder #3, and/or low compression in the cylinder. Best place to start is to make sure there is strong spark coming out of the coil. Next, remove the spark plug and look for any signs of problems, like cracked porcelain or a worn diode. If the plug, wire and coil check ok, move onto the fuel injector. You can run a simple test using an Ohms meter. Disconect the electrical connector, and take a resistance reading across the blades on the injector. If the resistance is not between 13.8 - 15.2 Ohms, the injector will need to be replaced. If all these check ok, you will then need to check for intake leaks, and ultimately, cylinder compression.
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