What Causes a Diesel Engine to Misfire?

A diesel engine misfire is an issue that occurs when a cylinder doesn’t ignite the fuel-air mixture adequately, resulting in incomplete combustion. This can cause the engine to run unevenly, increase emissions, and generate less power. You can usually identify one by noticeable shaking in the vehicle.

It’s integral to be aware of what causes a diesel engine to misfire before you can then learn how to fix or prevent it in the first place. Let’s take a look at some common diesel engine misfire causes below.

Issues such as clogged or malfunctioning fuel injectors can result in irregular fuel distribution to the cylinders, resulting in incomplete combustion. These issues are some of the most frequent causes of diesel engine misfires.

Glow plugs are crucial in preheating the air in the combustion chamber in cold weather. Malfunctioning or worn-out glow plugs can hinder ignition, leading to misfires, especially during cold starts.

A clean and unobstructed air intake system is essential for proper combustion. Dirty or clogged air filters or air leaks in the intake system can affect the air supply to the engine, causing misfires.

Proper compression is vital for efficient combustion. Problems with the cylinder's compression system, such as worn piston rings or damaged valves, can lead to incomplete combustion and misfires.

The engine's timing, controlled by the crankshaft and camshaft, must be precise. Any discrepancies in timing due to a faulty timing belt or chain can result in misfires. Also, malfunctioning sensors, like the crankshaft or camshaft position sensors, can disrupt the engine's timing and lead to misfires.

Issues with the exhaust system can impact the flow of exhaust gases. Blockages or leaks in the exhaust system can disrupt the engine's operation, potentially leading to misfires.

The Engine Control Unit (ECU) manages various engine functions, including fuel injection and ignition timing. Wiring problems, shorts, or issues with the ECU itself can cause misfires by sending incorrect signals to the engine components.

Diesel fuel quality is crucial. Contaminated or poor-quality diesel can result in incomplete combustion and misfires.

Fortunately, there are ways to address diesel engine misfire causes if you do come across them. You can follow the steps below:

Using inappropriate fuel can cause a diesel engine to misfire, so you should ensure you are utilising quality diesel fuel; inspect the diesel fuel to ensure the source has no contaminants like oil or dirt. Use appropriate diesel fuel additives if needed.

Inspect the fuel system service log and replace any fuel filters if necessary. Drain the water from the fuel system with a fuel water separator to prevent corrosion and fuel contamination.

A common issue with fuel lines is that the connectors can become corroded, preventing a good seal between the pipes and the fuel component. It is essential that fuel lines do not exhibit any signs of corrosion within the pipe and around the sealing area. If the fuel pipes are showing signs of corrosion, they should be replaced.

Check that no bends or kinks may restrict fuel flow in the fuel line and transfer pump. This may be causing reduced pressure and affecting fuel delivery to the engine.

To ensure the engine's fuel flow is not restricted, check that the suction pipe and suction hole are not clogged. Inspect for any blockages or debris clogging this area and clean or replace the components as necessary.

If the pressure is lower than specified, you may have a dirty or blocked fuel filter that needs replacing.

Air can disrupt fuel delivery. Bleed the fuel system to remove air bubbles and ensure the fuel lines are adequately sealed.

Inspect the return valve to ensure it is operating properly and that the poppet can move freely and seal correctly. If your return valve is faulty, you may consider replacing the transfer pump to restore proper fuel pressure regulation.

If you don’t think any of these common diesel engine misfire causes are the culprit in your case, our team may be able to detect another cause. Fortunately, engine misfire causes are typically straightforward to address and don’t indicate that something too severe is wrong with your diesel engine.

While it can be useful to know how to fix diesel engine misfire causes, it’s even more valuable to know how to prevent them from occurring in the first place.

One of the best ways to keep your diesel engine in good condition is to engage in regular maintenance and checks, always sticking to the manufacturer’s recommended maintenance schedule.

To prevent your fuel injectors from getting dirty, clean them regularly and avoid unnecessary clogging. If they start showing signs of wear and tear, replacing them sooner rather than later can help prevent diesel engine misfires.

Diesel engines may be sensitive to rapid temperature changes, so you should gradually warm your engine up before driving off. This is particularly important when the weather is cold.

Frequently tune your engine according to your vehicle’s specifications. This will make it likelier to function at maximum efficiency, which can prevent a diesel engine from misfiring.

Glow plugs are crucial in starting and stabilising your diesel engine, so you should monitor their performance and replace them if they show wear or damage.

Diesel engine misfires can be frustrating and detrimental to engine performance and fuel efficiency. Understanding a diesel engine's various systems and components and their potential for misfires is key to timely diagnosis and effective troubleshooting. Regular maintenance, proper fuel quality, and vigilance in monitoring and addressing these common misfire culprits can help ensure your diesel engine continues running smoothly.

If you want more useful information on anything from engine oil leak causes to common diesel engine overheating causes, please check out our blog.

However, if you’ve done your homework on the most common diesel engine problems and solutions and still think you would benefit from replacing your engine or getting a regular maintenance check, please get in touch with our team. You may also be interested in browsing our range of reconditioned diesel engines and diesel engine parts.