Diesel Car Won’t Accelerate: 9 Common Reasons (Solved)

The best part of driving any diesel car is the reliability and longevity you get from the diesel engine.

But what happens when the diesel car refuses to accelerate?

No or poor acceleration is a sign of a serious problem with the website and here are 10 common reasons why it happens.

Issues With the Air filter

One of the reasons for no or poor acceleration could be the lack of adequate air for the engine. 

The excessive pressure on the engine can cause a lot of strain on the diesel car.

Here are a few things you can do to check if lack of air is causing acceleration issues:

  • Clean the engine air filter as a clogged air filter can disrupt the air/fuel mixture that reaches the engine. The mixture isn’t at a factory-recommended level, resulting in poor performance and acceleration.
  • Keep the fuel injectors clean. Clogged fuel injectors cause a lot of strain on the diesel car, especially at higher altitudes.

There Might Be Something Stuck Under The Gas Pedal

Getting something like rumpled junk out from under the gas pedal is just another one of the quick fixes for an issue of poor acceleration.

That is because when something gets stuck under the pedal, you can’t apply the right pressure to it.

This limits your control over the acceleration and deceleration of the diesel car.

Sometimes poor acceleration is as easy to fix as cleaning the driver’s seat and foot area thoroughly before driving.

The foot mat or carpet is often slightly wedged under the gas pedal and prevents it from working properly.

If the gas pedal is stuck, there might be a problem with the electric throttle body.

Emergency Brakes Are Engaged (Partly Or Fully)

Another issue that causes poor acceleration is the emergency brake being engaged. It happens because the emergency brake presses the brake pads on the diesel car’s rear tires.

It makes the brakes drag.

However, this issue can be easily fixed by disengaging the emergency brake.

If the diesel car still goes into poor acceleration, there might be a problem with the diesel car’s rear brake pads.

You could take the diesel car to the mechanic for inspection if the bearings and wheel drums were caused by friction or overheating.

The Diesel Car May Be Running Low On Fuel

The fuel is the first thing to check when the diesel car undergoes slow acceleration. It’s another quick fix that doesn’t cost a lot.

Although there can be several other reasons for slow acceleration, not having enough fuel reaching the engine is a primary one.

It’s either a near-empty fuel tank or bad gas filled with dirt and debris. The debris can clog the fuel lines and filter, preventing the fuel from reaching the engine.

Poor quality diesel can also cause many issues, including slow acceleration.

Fill the tank with the right fuel to fix the issue.

The Engine Has a Faulty Catalytic Converter

A catalytic converter cleans the emissions from the engine, protecting the engine from pollution.

The converter can suffer a malfunction due to some damage on the road, but a few problems within the engine can also cause it to fail.

Two of the most common reasons why a catalytic converter fails are:

  • Spark plugs failure
  • A faulty oxygen sensor

If the catalytic converter malfunctions and fails to allow any emissions to escape from the engine, the whole exhaust system of the diesel car can be thrown out.

A bad exhaust system can be the cause of slow acceleration, which is why you need to fix or replace the converter once you locate the issue.

Transmission Failure

A transmission failure is something every driver dreads due to the back-breaking costs that follow it, but sometimes there’s no way out.

A common indicator of a transmission failure is no or slow acceleration.

The transmission works by transferring power from the engine of the diesel car to its driveshaft.

Here are some signs that the transmission of the diesel car is not working properly:

  • The gears either stick or shake.
  • Lack of power even though you step on the gas.
  • The engine starts missing when you accelerate.

Towing heavier objects with a diesel car can also leave a strain on its transmission very easily. Low transmission fluid may be the cause behind the transmission failure.

If you continue to overstrain the transmission without getting it inspected, the result would be the transmission overheating and affecting its fluid levels, causing a leakage.

Hence, get a transmission replacement if the mechanic instructs before it completely wrecks the diesel car, causing further problems.

Dirty Filters Or Sensors Can Cause Slow Acceleration

Smaller interconnected parts that keep the diesel car running can also get clogged easily due to the airflow. For instance,

  • A dirty air filter can prevent proper combustion in the engine. The diesel car’s manual indicates how often the air filter within it should be replaced.
  • A fuel filter protects the engine from debris and sludges it into the gas tank. A clogged one can prevent the fuel from reaching the rest of the diesel car.
  • Spark plugs and faulty ignition coils can result in engine misfires. When a spark plug hits the cylinder at the wrong time, it might not do anything, but enough misfires can lead to major acceleration problems in the diesel car.
  • A clogged fuel injector stops fuel flow as well. Adding a cleaning additive to the gas tank might solve the issue.
  • A mass airflow sensor calculates how much air is flowing into the engine. A clogged sensor might not take an accurate reading, which could result in major engine problems, including poor acceleration.

If all else is checked, inspect the smaller parts like the sensors and the filters within the engine bay.

Clean or replace them to fix the acceleration issue and prevent other issues from occurring.

Low Compression Of The Combustion Engine In A Diesel Car

The compression ratio is the ratio between the cylinder volume when the piston is at the lowest point and the volume at the highest point.

Compression is essential for the efficiency of a combustion engine.

Higher compression means a more forceful explosion that creates a lot more noise. However, if there is a fuel leakage in the diesel car, it can suffer from low compression and ultimately perform poor acceleration.

Here are potential reasons the engine undergoes low compression.

  • The piston rings are worn or cracked.
  • The valve springs wear out.
  • The valves may be worn out, or there’s a carbon buildup around the valve seats.
  • The cylinder linings wear out
  • Blown head gaskets are another reason behind low compression.

These above-mentioned issues will make the combustion gasses leak from the combustion chamber, resulting in low compression.

Hence, if you want the diesel car to have better compression, fix these smaller issues.

The Car Enters A Limp Mode

If the diesel car ceases to go above 25 or 40 mph, it may be because it has engaged in limp mode.

The limp mode is a security function for both the vehicle’s engine and transmission.

If there’s a problem with any one of the powertrain’s components, the vehicle enters limp mode.

Rather than completely shutting the car down, the limp mode allows it to limp to the destination without any further damage to the engine or transmission. Since it’s a preservation feature, it can slow down the diesel car to an extent.

An engine check light can switch on due to limp mode so you can be notified that the diesel car will safely drive until you reach the destination.

The diesel car enters the limp mode when it detects a fault within the system. For instance,

  • If the diesel car has an errant sensor.
  • Excessive engine knocks might trigger the limp mode.
  • There’s a problem with the emission control system.

The best thing to do when the diesel car enters limp mode is to take it to the nearest mechanic so they can inspect and correct the fault,

When the diesel car is in limp mode, the acceleration decreases automatically.

Clutch Failure

Acceleration issues occur when the clutch cannot effectively engage the transmission fluid with the engine of the diesel car.

This might be identified by the change in speed of the diesel car without the driver’s control.

If the car accelerates or decelerates by itself, there might be a problem with the transmission fluid reaching the engine or a failing clutch.

Malfunction Of The Electronic Control Unit (ECU)

After calculating the information delivered by the sensors within the diesel car, the ECU or electronic control unit affects the fuel and energy output.

But, if there’s a problem with one of the sensors, the electronic control unit can malfunction and read the wrong airflow.

It can also detect problems on its own, like pollution when there isn’t any.

This can lead to numerous problems. Hence, it’s best to take the diesel car to a mechanic for inspection.

Faulty Throttle Position Sensor

The TPS is responsible for monitoring the angle of the throttle and signaling the diesel car’s ECU on how to adjust the system properly.

If there’s a problem with the position sensor, it may monitor the angle inaccurately and result in poor acceleration.

You can replace the throttle position sensor or clean it to prevent further issues with the diesel car.

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