Misfire Codes and Ignition Coils

Understanding Misfire Codes And Ignition Coils

In a perfect world, a flashing check engine light for DTCs P0301 through P0312 would always be solved by installing a new ignition coil. If this were true, technicians wouldn't need countless hours of diagnostics training. The reality is that a misfire can be more than a missing spark from an ignition coil.

Sponsored by NGK Spark Plugs

In a perfect world, a flashing check engine light for DTCs P0301 through P0312 would always be solved by installing a new ignition coil. If this were true, technicians wouldn’t need countless hours of diagnostics training. The reality is that a misfire can be more than a missing spark from an ignition coil.

The Nature of Misfires

Misfires that are below the vehicles threshold often pass unnoticed, but a constant misfire is hard to be overlooked by you or the engine management system. These misfires would set a DTC inside the engine computer. Misfires that turn on the check engine light and log a cylinder-specific fault code are the easiest to diagnose, while random misfire codes can be more troublesome. The OBDII system can identify the cylinder(s) that are not contributing their normal dose of power and set a corresponding DTC. A P0303 DTC, for example, would indicate a misfire on cylinder number 3. If the ODBII system is unable to identify a specific cylinder a P0300 random cylinder misfire DTC will set. But, neither of these mean that the ignition coil or any other specific part is at fault. It simply means that more testing is necessary.

Coil Failures

Ignition coils can vary greatly in size and shape but share three common parts. These are the primary windings, secondary windings and a non-conductive or dielectric insulation material that separate the two windings. The insulation material is typically a dielectric resin that is applied in a vacuum, so air bubbles are not formed. Air bubbles can create a path for electricity inside of a coil, and lead to premature failure.

Coils fail for a variety of reasons including heat, vibration, or issues on the secondary side of the ignition system. Coils are commonly found bolted to the cylinder head, either on top or inside of a cylinder specific well. Excessive heat and vibration can cause the insulating material to break down and create internal coil failure. Worn secondary ignition components such as spark plugs or wires can cause a coil work harder, require more voltage, and therefore significantly reduce the operating life of the coil. When a coil fails, it is possible the electricity created is unable to reach its destination, the spark plug. When this happens, the electricity created inside of the secondary windings looks for the path of least resistance to ground. This path is commonly found through the boot or body of the coil. Carbon tracking happens when oil, dirt, or moisture is electrostatically attached to the boot or insulator and creates a path to ground. When carbon tracking is found, the coil and corresponding plug should be replaced. It is also possible that a failed ignition coil can cause damage to the engine computer, or ignition control module.

Non-Coil Misfires

Commonly an engine computer detects a misfire by measuring the changes in crankshaft speed. This change in speed can be caused by a combustion event that is happening early, late, or not at all.

Worn spark plugs are one of the leading causes of misfires on a high-mileage engine. Over time, the large amount of voltage needed to create a spark erodes the electrodes, increasing the gap. This change in the spark plugs gap increases the voltage required to generate a spark. Eventually, the ignition system reaches a point where it fails to jump that gap, and the spark plug does not fire.

The air/fuel ratio can also cause a misfire. The state of the fuel and air charge (too rich or too lean) inside the cylinder changes how the spark forms and how much voltage is required to jump the spark plug gap, and create spark.

A lean misfire occurs when the predetermined air/fuel ratio is more air than fuel, or in extreme cases all air and no fuel. This can be caused by a fuel injector not spraying, a faulty EGR system, or anything that is forcing more air into the cylinder than the engine computer had planned for. A rich misfire is less common than a lean misfire. The most common rich misfire is caused by a leaking or stuck open fuel injector. Rich or lean misfires can also be caused by a failed oxygen sensor. The engine computer monitors the oxygen sensor to report back the efficiency of the combustion event. A skewed or dead oxygen sensor can cause the engine computer to incorrectly add or subtract fuel.

Replacing an ignition coil before diagnosing what is actually causing the misfire may seem like a tempting diagnostic shortcut. But, it can really set you back in your diagnostic process. So the next time you get a vehicle in your shop with a misfire, don’t just assume it’s a bad coil. Test, don’t guess.

For more information or questions about spark plugs you can reach out to the NGK Technical Support line by calling 877-473-6767 or visit them on the web at www.ngksparkplugs.com.

 

You May Also Like

A Closer Look: Gasoline Direct Injection (GDI)

Gasoline direct injection (GDI) is used on most new vehicles and requires a different approach to diagnosis and service. GDI technology has been an integral part of helping to improve fuel economy while reducing emissions, and can be found on more than half of the U.S. fleet. In fact, the use of GDI engines has

Gasoline direct injection (GDI) is used on most new vehicles and requires a different approach to diagnosis and service. GDI technology has been an integral part of helping to improve fuel economy while reducing emissions, and can be found on more than half of the U.S. fleet. In fact, the use of GDI engines has grown by over 600% since 2010. This means that in the next five years, 42 million more vehicles with GDI will enter the Aftermarket “Sweet Spot” of 6-12 years old, during which their injectors and related parts may need to be serviced or replaced. While GDI systems have proved effective, these systems encounter specific failures and require an understanding of how they work and how to test them when they set a code.

A Closer Look: Electronic Throttle Bodies

A shop’s reputation is affected by things like accuracy of diagnosis, quality of the repair, and friendly service. Equally as important is the quality of the parts installed. If the shop does everything right, and the part fails, the customer will ultimately be upset with the shop. When a new part fails, the customer is

Enhancing Efficiency and Streamlining Operations: The Benefits of Utilizing Nexpart Multi-Seller for Repair Centers

In today’s fast-paced automotive repair industry, staying ahead of the competition is crucial for repair centers to thrive. One key aspect that can significantly impact operational efficiency and customer satisfaction is the availability of OE, Aftermarket, Heavy Duty & Salvage parts. Here are just a few advantages of incorporating Nexpart Multi-Seller, a cutting-edge parts ecommerce

Get your vehicle road trip ready with these summer tips 

Summertime is a great time to take your car out on the open road, but it’s also important to ensure that your vehicle is in tip-top shape. Regular preventative maintenance can help you avoid costly repairs and keep your car running smoothly. Make sure you’re ready with these helpful tips from Delphi Technologies. Chassis The

A Closer Look: Ignition Coils

OE coils are known for their high failure rates. Engine misfires, rough idle, a decrease in power under acceleration, poor fuel economy, and a check engine light are all signs of an ignition coil that has failed. Read along for more technical information on how to diagnose a failed coil, and why the original equipment

Other Posts
NGK Spark Plugs Expands Spark Plug, Ignition Coil Coverage

Expansion includes 15 new spark plug part numbers, many with high ignitability designs.

Training Opportunities for Service Advisors

Learn about the different resources available to educate service advisors on sensors and ignition components.

New ShopSquad Podcast Offers Interactive Tech Training Support

Watch Philip Austin from NGK/NTK and Doug Kaufman discuss management and technical challenges within the industry.

Engineering behind chassis: high and low-friction parts

What is overengineering? Overengineering is often described as designing a product or solution in an unnecessarily complicated way where a simple solution had been shown to have the same efficiency, or is even more effective than the original.  In the aftermarket world, the OE part is where the journey starts. It begins with testing and