Why Diesel Car is Losing Power When Accelerating

Regardless of whether it’s powered by petrol or diesel, every internal combustion engine needs certain elements in order to function correctly. These are clean fuel and air present in the correct proportions, a means of igniting the fuel and solid seals to maintain the compression necessary for the gases generated to drive the engine. A problem with any of these elements may lead to a car losing power.

Some of the common causes of a diesel car losing power when accelerating are as follows.

A Clogged Fuel Filter

Fuel filters prevent dirt or debris from entering the fuel pump, over time they get dirty and clogged. This results in fuel being delivered inefficiently. You might notice this most when you’re going uphill or accelerating to overtake. If your car loses power then comes back when the engine is under less strain, the fuel filter is the first thing to check. It’s generally a simple thing to change and will make a real difference to engine performance.

A Dirty Air Filter

Clean air is as important to the running of your car as clean fuel. A dirty air filter reduces the amount of air that enters the engine and has a negative impact on your car’s performance. Changing the air filter should be a standard part of your routine servicing but if you do most of your driving in rush-hour traffic, which often means sitting in a jam while your car takes in the dirty exhaust fumes of the vehicle in front, you may need to change the air filter more often than service guidelines indicate.

Man check and repair his car

Low Compression

If the cylinder compression is low the engine doesn’t generate enough power to run efficiently. This will be a problem whenever you’re driving but you’re more likely to notice it when you’re asking most of the engine while accelerating for example. Establishing that an engine has low compression is one thing, finding out why is another. Possible causes include worn piston rings, but it could also be a problem with the intake or exhaust valves, a blown head gasket or even a crack in the head of the piston.

Bad Fuel Injectors

Fuel injectors spray fuel into the combustion chamber. If too much or too little is injected the combustion cycle gets disrupted and that can result in loss of power. A fuel injection problem can lead to serious damage to cams or pistons so it’s a fault that needs to be corrected quickly to avoid a hefty bill down the road.

Faulty Glow Plugs

Glow plugs preheat the engine cylinders so that the diesel ignites more easily. Faulty glow plugs can be responsible for a car losing power but are also likely to cause other symptoms, most notably difficulty starting when cold.

Driving car at night

A Clogged Catalytic Converter or Exhaust Pipe

If either of these are clogged, gases can’t easily exit the engine, this generates something like a ‘backpressure’ which makes it hard for the engine to function properly and will result in less power and poor acceleration.

Electronic Faults

At the simple end of the spectrum, a dodgy connection could cause an intermittent fault. If your car loses acceleration then comes back, something as minor as a loose connection could be the cause. However, the more sophisticated cars get, the more potential there is for a computer fault to cause a problem. An oxygen sensor malfunction or any of a myriad of other engine management system faults can detect that something is not quite right and put your car into ‘limp mode’. You’ll curse this if you’re in a hurry but it’s a safety feature designed to protect your engine from serious damage.

The Dangers of Poor Acceleration

Pulling away slowly from the lights or a junction may be no big deal but the loss of power can leave you quite vulnerable when overtaking. If you realise your car is losing power when accelerating you may be able to nurse it to your usual garage. If however, the fault is serious enough to reduce your capacity to react to an emergency you’d really do better to find a safe place to pull in and arrange recovery. However much this might disrupt your plans for the day it’s still a better option than being involved in an accident.