Karlyn Industries/STI distributes high quality COP components. Karlyn Industries/STI utilize independent engineers to monitor their coils and test warranties. Most coils that are returned do not have a problem. Rough running engines that set misfire codes can have multiple causes. It is the responsibility of the dealer/installer of their products to verify that the following items of inspection have been performed, in order to comply with warranty replacement. General misfire codes are most likely due to an intake vacuum leak or fuel delivery problem. Misfire codes identifying a particular cylinder are usually due to a fouled spark plug, dirty or dead fuel injector or loss of compression in the cylinder burned or bent valve, weak or broken valve spring or leaky head gasket. If the crankshaft position sensor fails, the loss of the basic timing signal will prevent the system from generating a spark and the engine will not start or run. A failed driver circuit within the power train control module (PCM) can kill an individual coil and prevent that cylinder from firing. Replacing the coil without addressing the cause will only result in another damaged coil. Misfire codes can also be triggered from a damaged wire harness due to poor grounds. Inspect the wire harness carefully. You may have to cut back the insulation to verify that there is no corrosion or melting of the wire harness due to poor grounds. A faulty harness can cause the coil to fail. If you simply install a new COP it may seem like you have corrected the problem but, merely replacing the coil without repairing the grounding problem may result in future coil failures. In summary, it is important to remember that ignition misfire can also be caused by other factors such as worn or fouled spark plugs, loose or damaged coil connectors or terminals, dirty fuel injectors, low fuel pressure, intake vacuum leaks, loss of compression in a cylinder, even a tankfull of "bad" gas contaminated with water. These other possibilities should all be ruled out before a COP unit is replaced. Note: A fouled sparkplug can damage the COP. Karlyn STI recommend that you always replace the spark plugs when you replace the COP units and that all the ignition coils be replaced at the same time. As a form of preventive maintenance we suggest this be done every 60,000 miles Karlyn Industries/STI will do their job to monitor and test the integrity of their coils. Karlyn STI hope that this information will help you to enhance the reliability and credibility of your repair while complementing their product. The main goal here is a real solution to your ignition problem which will result in happy customers. Temporary solutions will only result in the return of non-defective parts and unhappy customers who will continue to have the same problem.