Diesel cars – why they lose power over time

Diesel cars – A small parenthesis

Diesel cars are made to be driven frequently for long motorway journeys, not for city traffic. Stop-and-go traffic kills diesel engines, which burn out slowly like candles in the night.

In the 1980s, fuel injection replaced the carburettor. Since then, the car’s performance has improved considerably and at the same time, fuel consumption has been reduced. Time ago, diesel engines ran on almost anything that burned, but with modern cars, this is no longer the case. The injection system does not work uniformly. On the contrary, it adapts itself at all times, considering various parameters: outside temperature, acceleration power on the pedal, engine speed or weather conditions. 

Its task? To supply the engine with the exact amount of fuel it needs at instant T. This is sent into the injector and comes out pulverised into droplets, depending on the desired amount.

Diesel engines, often called ‘self-igniters,’ can ignite fuel without a spark plug. Unlike their gasoline counterparts, diesel engines rely solely on the compression pressure generated by the upward movement of the piston to trigger the desired explosion within the diesel-air mixture.

Advantages of Common Rail Diesel Injection

Modern Diesel engines equipped with common-rail fuel injection technology can exhibit efficiency levels up to twice that of petrol engines. The advantages of utilising common-rail diesel injection are numerous and far-reaching:

1. High Injection Accuracy: Unlocking Precision

Implementing diesel injectors ensures high injection accuracy, allowing for precise fuel delivery. This precision enables optimal combustion and enhances overall engine performance.

2. Total Control over Diesel Injection Parameters

With common-rail diesel injection, complete control over crucial injection variables, including pressure, timing, speed, and fuel quantity, is achieved. This level of control empowers manufacturers to fine-tune the combustion process, resulting in improved efficiency and reduced emissions.

3. Reduction of Engine Pollutant Emissions: A Cleaner Future

The precise management of diesel injection facilitates the reduction of pollutant emissions, contributing to a cleaner environment. Common-rail diesel engines minimise harmful exhaust gases by carefully regulating the fuel-air mixture and optimising combustion.

4. Optimised Performance and Fuel Economy: A Winning Combination

Common-rail diesel injection technology optimises both engine performance and fuel economy. By precisely delivering the appropriate amount of fuel at the right moment, diesel engines can achieve remarkable efficiency gains, resulting in fewer trips to the pump and more miles on the road.

5. Increased Engine Power and Reduced Noise Level: A Harmonious Blend

Implementing common-rail diesel injection enhances engine power output, unlocking more significant performance potential. Simultaneously, it contributes to reduced noise levels, ensuring a quieter and more comfortable driving experience.

However, there is always a ‘but’! It is essential to note that maintaining the superior efficiency of a diesel engine, in comparison to a similarly-sized petrol engine, relies on the optimal functioning of various factors and control systems. Any lapse in the operation of these elements can progressively diminish engine power and compromise overall efficiency, mainly as mileage accumulates over time.

Potential causes to consider for power loss and reduced efficiency in diesel engines

1. Fuel System Issues

   One of the primary culprits behind diesel engine power loss is fuel system problems. These can include:

   • Injectors issues

     Poor quality fuel leads to clogged injectors. If the injectors become clogged, they can no longer distribute the fuel in the combustion chamber evenly. If the droplets are too large, the diesel does not burn completely. If they are too small, the engine heats up too much and does not run properly.

     
     

     Incomplete combustion results in carbon build-up, and when carbon deposits begin to develop, fuel consumption increases, and the engine loses power. From an ecological point of view, this means more CO2 and pollutants being released into the atmosphere. It is necessary to recognise the symptoms that can signal when it is time to clean the injectors. Here are some of the symptoms, but are not limited to, rough running at idle, visible smoke from the exhaust, increased fuel consumption, clogged or damaged catalytic converters and/or DPFs (Diesel Particulate Filters), frequent DPF regenerations or failure to initiate DPF regeneration, and power loss.

     
     
   • Clogged fuel filters

     Fuel filters are crucial in removing impurities and contaminants from the fuel before it reaches the engine. Over time, these filters can become clogged, obstructing the flow of fuel and reducing engine power. The filter problem often manifests itself when driving uphill or trying to overtake a car, as the necessary power and acceleration cannot be achieved. Regularly inspecting and replacing fuel filters can help prevent this issue.

   • Fuel Contamination

     Contaminated fuel, such as water or debris, can cause blockages in the fuel lines and injectors, disrupting the combustion process. Regularly monitoring fuel quality and using fuel additives or treatments can minimise the risk of fuel contamination.

2. Air Intake System Restrictions

   A restricted air intake system can limit the amount of air available for combustion, leading to a loss of power. The following issues can cause air intake restrictions:

   • Dirty Air Filters

     Air filters trap dust, dirt, and debris, preventing them from entering the engine. Over time, these filters can become clogged, restricting airflow. Regularly replacing air filters can ensure optimal engine performance.

     
     
   • Blocked or Damaged Air Ducts

     Obstructions or damage to the air ducts can impede airflow into the engine. Inspecting and clearing blockages or repairing damaged ducts can help restore proper airflow and engine power.

3. Engine Mechanical Problems

   Several mechanical issues can contribute to a loss of power in diesel engines. These include:

   • Compression Loss

     Loss of compression occurs when the combustion chamber fails to seal properly, leading to power loss. Common causes include worn piston rings, cylinder head gasket leaks, or damaged valves. A car inspection by a specialised mechanic who will also do a compression test will tell the causes of compression loss and how to solve the problem. Photo credits checkengine.com

   • Turbocharger Malfunction

     Turbochargers increase the airflow into the engine, boosting power output. If a turbocharger malfunctions or develops issues like worn bearings or damaged compressor blades, it can result in power loss. Remember that more than 90% of turbocharger failures are caused by poor oil lubrication or contamination. Rebuilding the turbocharger will cost less than buying a new one but will take longer because the disassembled turbocharger will have to be sent to a specialised centre and wait for it to return so that it can be fitted to the car.

     
     

4. Exhaust System Restrictions

   An obstructed exhaust system can hinder the efficient flow of exhaust gases, causing a decrease in engine power. The following factors can contribute to exhaust restrictions:

   • Clogged Catalytic Converter or Diesel Particulate Filter (DPF)

     The catalytic converter and DPF reduce emissions in modern diesel engines. Over time, they can become clogged with soot and other deposits, impeding the exhaust flow. Cleaning or replacing these components can restore power and improve engine performance.

     
     

     Photo credits dpfaustralia.com.au

   • Exhaust Leaks

     Leaky exhaust connections or damaged pipes can result in loss of exhaust pressure, negatively impacting engine power. Repairing or replacing the affected parts can resolve this issue.

     
     

Conclusion

Diesel engine loss of power can stem from various factors related to the fuel system, air intake system, engine mechanics, and exhaust system. Regular maintenance and troubleshooting can help identify and address these issues promptly. By paying attention to these potential causes and taking appropriate actions, you can optimise the performance of your diesel engine and ensure maximum power output.

If you want to understand better how a diesel engine works, watch this video: