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Bad Ignition Coil Symptoms: 5 Signs You May Need a Replacement
All cars have an ignition system with one or more ignition coils. Ignition coils are designed to convert the low-voltage from the battery into the high-voltage needed to fire the spark plugs.

Because ignition coils are such an integral part of the ignition system, they almost always cause noticeable symptoms when they fail.

Signs of a Bad Ignition Coil

Do you think your car might have a bad ignition coil? If you’re experiencing one or more of the following symptoms, you may be right.

Engine Misfire

Since ignition coils play a role in igniting the engine’s air-fuel mixture, a faulty coil can easily cause a misfire. A misfire happens when there’s incomplete combustion (or zero combustion) inside one or more of the engine’s cylinders.

The phenomenon will feel like a hesitation or shaking when the car is running. You may notice the problem intensifies when the engine is under a heavy load (e.g., accelerating).

Illuminated Check Engine Light

On modern cars, a computer (often referred to as the powertrain control module), looks for problems that could potentially lead to an increase in vehicle emissions. One such problem is an engine misfire caused by a faulty coil. The PCM will usually detect the misfire—and possibly an issue with the coil’s electrical circuit—and turn on the check engine light.

Car Won’t Start

While most modern engines have one ignition coil per cylinder, older vehicles use a single coil to supply voltage to all of the spark plugs. If that lone coil fails, none of the cylinders will receive spark, resulting in a car that cranks but doesn’t start.

The Engine Stalls

Like most electrical devices, ignition coils can experience intermittent problems. When this happens, the engine may stall unexpectedly. Stalling mostly happens to engines with just one ignition coil.

Reduced Fuel Economy

A faulty ignition coil usually results in an engine that misfires and runs poorly, leading to a reduction in fuel economy.

What Does an Ignition Coil Do?

An ignition coil is a transformer that converts battery voltage into the tens of thousands of volts needed to fire the spark plugs. Ignition coil operation is based on a phenomenon called electromagnetic induction—a process that uses a magnetic field to generate electrical current.

Inside the coil, there are two sets of windings. The so-called primary windings contain a hundred or so coils of wire, whereas the secondary windings have thousands of coils of wire.

When the ignition coil is energized, battery voltage flows through the primary windings, creating a magnetic field. Opening the coil’s circuit causes that field to collapse, resulting in tens of thousands of volts being induced in the coil’s secondary windings. The high voltage from the secondary windings then travels from the coil to the rest of the ignition system.

It’s important to note that there are different types of ignition coils. Older vehicles have a single ignition coil that’s connected to a distributor via an ignition wire. High-voltage travels from the coil to the distributor, which, in turn, distributes that voltage to the individual spark plugs and wires.

Newer vehicles use either coil-on-plug (COP) ignition coils or coil packs. Engines with a COP ignition system have one ignition coil per cylinder. Each coil sits directly on top of a spark plug.

Meanwhile, a coil pack is a group of ignition coils combined together in a single molded block. With this design, each cylinder gets its own ignition tower but shares its coil with a companion cylinder.

How to Test a Two-Stroke Engine's Ignition Module and Coil
The ignition coil or module for a two-stroke engine regulates the ignition power, and converts it to charging electricity for the battery system. When the module and coil begin to fail, it's typically because the units have been burned out. The result will be an engine that performs badly, if it starts at all. Testing such units involves using a few electrical tools to gauge if the part still works, since most modules and coils are sealed with no serviceable parts.

Step 1

Disconnect the spark plug cap from the spark plug. Carefully remove the plug wire to the ignition coil from its hooks that keep it in place on the engine. Pull the plug wire out of the coil where it inserts: It's typically just pushed-in onto a spike in the coil.

Step 2

Use a screwdriver to disconnect the coil unit from its harness, or bracket on the engine. Put the securing screws aside. Carefully pull the coil off the bracket, and then carefully disconnect the engine and vehicle wires from the coil itself.

Step 3

Attach the ends of a multimeter to the coil connections for input and to ground, testing electrical resistance in the unit. Replace the coil unit with a new one, if the reading shows as infinity or zero. This means that there is no resistance the unit is burned out.


When the spark travels to the spark plug, it jumps from the spark plug gap to the ground, causing an explosion of the fuel air mixture inside the cylinder chamber.

Coil Pack Problems

Usually, if a coil pack is bad, there will be a loss of fire or spark in one or more cylinders. This causes what's commonly referred to as misfiring. Misfiring can cause drag on the crankshaft, and usually results in a very poor performing engine.

Common Symptoms of a Faulty Coil Pack

A faulty coil pack will generally have symptoms similar to a faulty spark plug. Some of the most common tell tale signs that a coil may be defective include:

A rough idle

An unexplainably louder-than-usual engine

A noticeable lack of power

A significant drop in RPMs while accelerating for no apparent reason

A blinking or intermittently activating check engine light

An active gas warning light when the vehicle has plenty of gasoline

Smoke from the exhaust emitting intermittently, instead of in a steady stream

What Coil Pack Works with a Rotary Engine?
Most rotary engines require a different type of ignition coil pack. Below are two, one for a standard replacement, and one that is a higher voltage performance type coil pack.

Original Equipment Replacement

Beck Arnley is a well known name in the automotive ignition parts industry. They are favored by many mechanics, especially those that work mostly on import cars. The Beck Arnley 178-8025 rotary engine coil pack is a direct replacement for original equipment parts on older Mazda cars with a rotary engine. You can expect to pay about $55 for one.

Performance Replacement

M&W Ignition Systems is a fairly well known name in the import performance market. Their part number PAK005 is a high performance ignition coil pack for the performance enthusiast who isn't afraid to spend a little more on a high quality high performance part. With prices running around $245 for a double coil pack for direct fire ignitions, these coil packs will deliver years of excellent performance.

When ordering a coil pack for your rotary engine equipped car, you need to know the year and model as well as the engine displacement to ensure you are given the correct parts.