An ignition coil functions to provide sufficient voltage to produce spark in the spark plugs, and it acquires power from the battery to be able to do this job. It may seem like a very technical thing, and you might have an impression that only a professional could understand how it works. However, knowing when it is starting to malfunction is not too hard to learn. Here are the most common problems with a Jaguar Xj8 ignition coil and their causes:
An ignition coil usually fails because of overheating. In this case, you need to check the spark plugs for excessive spark gap. When the gap of spark plugs is too big, an additional voltage would be required for the spark to jump from one electrode to the next. As a result, the ignition coil heats up due to the additional load it carries. The coil tends to expand and contract during the overheating and cooling process, which results into its complete malfunction. Your engine may die all of a sudden without any warning. Sometimes, it won't even start at all, and the vehicle will run poorly or stop intermittently.
Confirm a faulty ignition coil by checking if it is properly mounted. Examine the external wires and spark plug wires if they are loose because problems with these wires could cause the ignition coil to arc itself. As a result, the coil may be damaged permanently.
You can try running the vehicle for around 30 minutes. Then, gently tap the module using the head of a screwdriver. If the engine dies, the ignition coil definitely needs to be changed. Another method is measuring the resistance of the primary coil with a multimeter. Simply touch the leads of the device to the poles on the exterior of the coil. If the reading is within the specifications, the primary coil is in good condition. Meanwhile, to test the secondary coil, attach one of the leads to the 12-volt pole and the other lead to the big pole in the middle. The resistance of a good secondary coil should match your vehicle's specifications. If it doesn't, a replacement would be necessary.