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Jaguar XJ8 Ignition Coil

How to Test a Faulty Jaguar Xj8 Ignition Coil

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.

Faulty connections

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.

Other tips on detecting a bad ignition coil

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.

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  • Keeping Your Jaguar Xj8 Ignition Coil in Excellent Condition

    Develop the habit of regularly checking your ignition coil before it's too late. A defective coil is usually the culprit behind many automobile problems such as sluggish running, spark plug misfiring, poor fuel economy, and engine start-up failure. You wouldn't want to experience any of these troubles, so make sure that your Jaguar Xj8 ignition coil is always in proper working condition. Here are a few tips to ensure that your ignition coil can still provide enough current:

    • Perform a visual inspection.
    • When checking the condition of your ignition coil, look out for cracks or any mechanical damage. Examine the electrical wiring and plugs for corrosion and kinks. Make sure that they are still intact and that there are no signs of wear. Also, the seals should not be exhibiting leakage.
    • Measure the resistance of the ignition coil.
    • The ignition coil is composed of the primary and secondary coils. To determine the primary resistance, simply connect the red lead of the ohmmeter to the coil's positive electrical connector and the black lead to the negative connector. Normal range of resistance is between 0.3 and 1.0 ohm. Meanwhile, secondary resistance can be measured by attaching the ohmmeter's black lead to the coil's negative connector. Then, connect the red lead to the terminal of the coil where the spark plug wire is attached. Average resistance is between 8,000 to 11,500 ohms.
    • Replace defective coil.
    • If the primary or secondary coil demonstrated a reading that is below or above the normal resistance level, replacing the coil would be needed. Before installing the new ignition coil, you may apply a thin layer of dielectric compound on it to prevent high voltage arcing and to exclude moisture. Make sure that the new coil is already properly adjusted to your car's engine and that the amount of torque applied on the bolts of the new coil is correct.
    • Keep the resistance low.
    • To prolong the life of your ignition coil, keep its resistance as low as possible. The lower the resistance of the coil, the more durable it becomes. You can do this by changing your spark plugs regularly. Plugs usually last for 25,000 to 50,000 miles.