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.





Take the good unit, or a new coil and reconnect it to the engine bracket. Insert a new length of spark plug wire, after connecting the spark plug cap to one end. Insert the other end into the coil receptacle for the wire. Reconnect the spark plug cap to the spark plug.


Ignition Coil: Basic Principles


The design of a conventional ignition coil is basically similar to that of a transformer. The ignition coil's task is to induce a high voltage from a low voltage. Alongside the iron core, the main components are the primary winding, the secondary winding, and the electrical connections.


The laminated iron core has the task of amplifying the magnetic field. A thin secondary winding is placed around this iron core. This is made of insulated copper wire about 0.05-0.1 mm thick, wound around up to 50,000 times. The primary winding is made of coated copper wire about 0.6-0.9 mm thick, and is wound over the secondary winding. The ohmic resistance of the coil is around 0.2–3.0 Ω on the primary side and around 5–20 kΩ on the secondary side. The winding ratio of primary to secondary winding is 1:100. The technical structure may vary depending on the ignition coil's area of application. In the case of a conventional cylinder ignition coil, the electrical connections are designated as terminal 15 (voltage supply), terminal 1 (contact breaker), and terminal 4 (high-voltage connection).


The primary winding is connected to the secondary winding via a common winding connection to terminal 1. This common connection is known as the "economy circuit," and is used to simplify coil production. The primary current flowing through the primary winding is switched on and off via the contact breaker. The amount of current flowing is determined by the coil's resistance and the voltage applied at terminal 15. The very fast current direction caused by the contact breaker changes the magnetic field in the coil and induces a voltage pulse, which is transformed into a high-voltage pulse by the secondary winding. This passes through the ignition cable to the spark plug's spark gap and ignites the fuel-air mixture in a gasoline engine.


The amount of high voltage induced depends on the speed of change in the magnetic field, the number of windings on the secondary coil, and the strength of the magnetic field. The opening induction voltage of the primary winding is between 300 and 400 V. The high voltage on the secondary coil can be up to 40 kV, depending on the ignition coil.


How to Tell if You Have a Faulty Coil Pack


On newer vehicles, a coil pack replaces the distributor. It is an electronically controlled pack of ignition coils regulated by the car's computer and is used to create the spark for each engine cylinder's spark plug. Generally speaking, coil packs are much more reliable than distributors, because there are no moving parts and because they fire much less often than a distributor. Coil packs usually create a better spark, which in turn produces better combustion and horsepower in a car's engine.


How a Coil Pack Works


When creating a spark at the spark plug, the fire must initiate from a high voltage supply, so as much fuel as possible burns in the cylinder. Whenever the combustion process is started, the coil pack builds up the energy, as much as 50,000 to 75,000 Volts. When the electronic control module (the car computer) sends the signal to the ignition control, the voltage is released from the coil pack through the spark plug cables to the spark plug.


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.