How do you diagnose a faulty coil?Įngine misfires or backfires, hard starting, a lack of power, poor fuel consumption, or the smell of unburned fuel in the exhaust are all possible indications of a faulty coil. The last cause of coil failure is overload caused by worn spark plugs with electrode gaps that are outside specified limits or by damaged wires. In time, the needed voltage can rise to levels, causing the coil to overheat and short circuit. These cracks can then allow moisture in to short out the windings intermittently, causing rough running.
If the internal insulation breaks down, it can cause a short in the winding, limiting the amount the voltage gets stepped up.Īnother way coils can fail is by developing cracks in their insulated case. Over time these forces can break up the coil’s windings and insulation. The biggest causes of failure in coil packs are heat and vibration, so a hot engine bay is a challenging place for it to live. Here the coil gets alternately hot and cold, and is subjected to strong vibrations from the engine. The primary wire receives the low voltage from the battery which generates a magnetic field around it. However, the instant that flow is interrupted by the ignition system or electronic control unit (ECU), the magnetic field collapses, creating or inducing a higher voltage in the secondary wire that travels to the spark plug. If you'd like, the Wikipedia article on transformers goes into great detail. It does this using two separate coils of wire with both coiled around a central core, all contained within an insulated body. One wire, called the secondary, is made up of thousands more windings than the other one, called the primary. The difference in the number of windings (imagine a spool of thread) determines the level of voltage that comes out for a given input. For this reason, a modern engine can have multiple coils.Ī coil works on the simple electrical principle of the step-up transformer. On modern cars with an electronic ignition system that uses a computer rather than a distributor to fire the spark plugs at the right time, the coil is likely to be mounted directly to the spark plug, or close by, without the need for high voltage spark plug wires. If the car is an older model, the coil is typically mounted to the firewall or the engine near the distributor that ‘distributes’ the high voltage it produces to each spark plug, via thick rubbery spark plug wires. The engine computer sends 12 volts to each coil in turn to fire the plugs when needed.
#Coolpack car series#
Others mount boxy coil packs to the fender, firewall, or motor, with short leads to the spark plugs. Some coils are constructed in series and called cassette or sequence coils, or coil rails. On a modern car, coils typically are mounted directly on top of the spark plugs, so the high voltage does not have far to travel.
Some systems, like the GM HEI distributor, mount the coil directly in the distributor cap, and look like #1 below. If your car is an older vehicle with traditional distributor ignition, it’ll look like a small metal cylinder (in fact, it’s often called a canister-type coil) with wires sprouting out of it, one connecting it to the battery, another to the distributor. A coil that is going bad can deliver a voltage that only fires the plug under certain conditions, causing an intermittent misfire. The pressures are so high in the cylinder that the voltage has to be extremely high for the spark to be effective. Why does an engine need one?Įngines need a coil because without it the spark plug wouldn't receive voltage high enough to do its job of igniting the fuel/air mixture in the combustion chamber. It is typically just a wire wound transformer filled with an insulator. The coil is the part of a car’s ignition system that takes the battery’s 12-volt output (called low-tension current) and transforms it into as much as 45,000 volts (called high-tension current) before then supplying it to the engine’s spark plugs. But the coil pack is this shadowy thing that many people wouldn't recognize and don't know the purpose of.
The same goes for the spark plug wires on cars that still use them. The spark plug is a familiar part of a car’s ignition system and one that is routinely replaced, typically as part of a car’s major service. The trouble is, the coil is an unknown quantity to many people. If you foul the catalyst with unburned fuel, it will be expensive to replace. This can be a serious issue, though not expensive to fix if caught early, because a car not running smoothly can damage the catalytic converter in the exhaust system.
If your car has trouble starting, runs rough, has a misfire, or is getting fewer miles to the gallon, it may be that there is a problem with the ignition coil, or one of the coil packs.
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