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Why Do Heavy Equipment Diesel Engines Misfire?

Why Do Heavy Equipment Diesel Engines Misfire?

A yellow backhoe working next to a gray wall on a construction site

Why Do Heavy Equipment Diesel Engines Misfire?

Reading time: 5 min 30 sec

Introduction to Diesel Engine Misfires

Engine misfires in heavy equipment, such as skid steers, dozers and excavators are a common indicator of a malfunctioning engine. 

Unlike gasoline engines that use spark plugs for ignition, diesel engines rely on high compression to heat the atomized fuel sufficiently, causing it to combust. A misfire occurs when the engine fails to complete the combustion cycle properly, leading to one or more cylinders not firing properly.

Compared to gasoline engines, diesel engines are more susceptible to issues related to fuel quality, injection timing and air intake. Therefore, misfires in diesel engines may indicate different problems. Understanding the causes and effects of misfires is essential for maintaining the health and longevity of equipment in your fleet. 

In this article, we’ll discuss the common causes of diesel engine misfires and how they can be prevented. Regular maintenance and early detection of misfires can prevent more significant damage to the engine and related systems, helping to mitigate excessive repairs and downtime.

The Causes of Engine Misfires in Heavy Equipment

Engine misfires can significantly impact the performance and lifespan of heavy equipment engines. Misfires occur when the engine fails to ignite the fuel-air mixture correctly, leading to incomplete combustion. This can result from several conditions.

Fuel System Issues

Fuel system problems are among the most common causes of engine misfires in construction equipment. Contaminated fuel can introduce water, dirt or other foreign substances into the engine, impacting the combustion process.

Clogged fuel filters similarly disrupt fuel flow, preventing the engine from receiving the proper fuel-air mixture for combustion. Additionally, malfunctioning fuel injectors, which fail to deliver fuel efficiently into the combustion chamber, can lead to misfires.

Air Intake Problems

Sufficient airflow is critical for efficient combustion. Airflow restrictions caused by clogged air filters or leaks in the air intake system limit the amount of oxygen available for combustion, leading to misfires. 

Turbocharger faults can also contribute to misfires in diesel engines. If the turbocharger fails to provide the necessary boost pressure, the engine won't receive the correct air-fuel ratio, resulting in inefficient combustion.

Glow Plug Failures

In diesel engines, glow plugs help facilitate the combustion process, especially in cold weather. Faulty glow plugs can lead to difficulty starting the engine or cause misfires during operation as they fail to properly heat the combustion chamber. The severity of glow plug failures can range from minor, affecting engine start-up, to more severe, affecting overall engine performance.

Compression Issues

Compression is essential for effective combustion in diesel engines. Worn components such as piston rings, cylinder liners and valves can lead to compression loss, preventing the engine from achieving the necessary pressure for combustion. These issues are often severe and may lead to significant damage if left unaddressed.

Electrical and Sensor Failures

Modern construction equipment relies heavily on electronic systems and sensors to regulate the combustion process. Failures within these electrical components, such as faulty sensors or wiring issues, can mislead the engine control unit (ECU), leading to improper fuel delivery, timing and misfires.

The Effects of Engine Misfires

Engine misfires can impact the performance and overall health of construction equipment. The immediate effects on performance include reduced efficiency and power, as misfires disrupt the engine's ability to convert fuel into mechanical energy effectively. 

This inefficiency often leads to increased fuel consumption, as the engine requires more fuel to achieve the desired level of performance. Additionally, misfires can cause uneven engine operation, resulting in rough idling and decreased operational smoothness.

The health of the machine suffers significantly due to engine misfires. Increased wear on engine components is common, as misfires cause uneven forces and temperatures within the engine. Over time, this can lead to significant engine damage, negatively impacting the engine’s lifespan.

Specific parts most impacted by engine misfires include fuel injectors and cylinder components (such as pistons and valves).

Initial Signs of An Engine Misfire

The initial signs of a misfiring engine, or one on the verge of misfiring, commonly include a few key indicators. 

Rough idling and noticeable vibration are common symptoms, signaling that the engine is not running smoothly due to incomplete combustion. A decrease in power or efficiency is another telltale sign, where the equipment may struggle to perform under typical workloads or exhibit sluggish response.

Increased fuel consumption is also an indicator, as the engine compensates for lost power by using more fuel, making operations less efficient and more costly. Excessive smoke from the exhaust, particularly if it's darker or more voluminous than usual, is another potential consequence of misfires.

Diagnosing Engine Misfires

Diagnosing an engine misfire often requires a combination of inspections, tests and diagnostic tools. Mechanics might start with a visual inspection for obvious issues, such as damaged components, but will typically rely on diagnostic tools that read engine codes and monitor engine performance to pinpoint misfires. Manual tests, including compression tests, can help verify the diagnosis.

Preventive Maintenance to Avoid Misfires

Preventing engine misfires in heavy equipment involves a proactive approach to maintenance. This includes using clean, high-quality fuel, regularly replacing fuel filters and ensuring fuel injectors are clean and functioning properly.

Care of the air intake system is also essential, involving the replacement of air filters and inspection for leaks or obstructions that could restrict airflow. Upkeep of the compression system, through the monitoring and maintenance of cylinder seals, piston rings and valves, ensures that the engine maintains proper compression levels for efficient combustion. Electrical systems and sensors require regular checks to ensure they are providing accurate information to the engine control unit (ECU), preventing misfires caused by faulty data.

Repair and Recovery

Repair times and costs for a misfiring heavy equipment diesel engine can vary widely, depending on the root cause of the misfire and the extent of any damage. Minor issues such as clogged filters or faulty sensors might be resolved within a few hours at a relatively low cost. However, more severe problems like damaged injectors or compression issues could require days of work and significantly higher expenses, potentially reaching thousands of dollars.

A complete engine overhaul or replacement is considered when the engine incurs extensive wear or damage that cannot be repaired or when repeated misfires and other problems lead to a loss of reliability.

Final Thoughts

Addressing engine misfires promptly in heavy construction equipment is crucial for preventing the escalation of damage that can lead to costly repairs and downtime.

If you’re looking to repair or prevent engine misfires, the EquipmentShare Shop is a valuable resource. With an extensive selection of OEM and aftermarket engine components, our online parts catalog can help you maintain your engine’s performance. Don’t see exactly what you’re looking for? Reach out to our dedicated parts experts and get personalized assistance.

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