Diesel Engine Using Too Much Fuel: Causes and How to Reduce It

Why a diesel engine uses more fuel than normal: injectors, filters, turbo, tire pressure, EGR, DPF and driving habits. How to diagnose it.

By Diesel Universal technical team3 min read

Key points

A rise in consumption can come from mechanical or injection causes, or simply from use and vehicle condition.
The most frequent causes are dirty filters, leaking or poorly spraying injectors, a faulty turbo and low tire pressure.
A sudden change in consumption deserves diagnosis; a gradual rise usually points to wear or lack of maintenance.
Measure consumption consistently before drawing conclusions.

A rise in fuel consumption is one of the most annoying symptoms because it is paid for every time the tank is filled. There is almost always a specific cause that can be measured and corrected: from something as simple as tire pressure to a problem in the injection system.

Before suspecting the mechanics

It is worth ruling out outside factors that change consumption:

Low tire pressure: increases rolling resistance.
Extra load, roof racks, a trailer or altered aerodynamics.
Driving style: hard acceleration and high speeds.
Short trips and city traffic, where the engine never reaches optimum temperature.
Variations from weather and altitude.
How it is measured: calculate consumption by filling the tank the same way each time and in similar conditions.

Mechanical and injection causes

Injectors

An injector that drips, has excessive return flow or sprays poorly burns more fuel than needed and usually produces smoke. It is a very frequent cause. See bad diesel injector symptoms and diesel injector test bench.

Dirty filters

A clogged air filter reduces available air and worsens combustion; a clogged fuel filter strains the pump. See how often to change the diesel fuel filter.

Turbo

A turbo that does not give the right pressure makes the engine work harder. See diesel turbo failure.

Injection pump

A pump that is out of calibration or worn can deliver more fuel than appropriate or with incorrect timing. See types of diesel injection pumps.

Emissions systems

A DPF with frequent regenerations uses extra fuel to burn off soot, and a clogged EGR worsens combustion. See what is a DPF and EGR valve problems.

Sensors

Temperature, airflow or pressure sensors with wrong readings can make the ECU enrich the mixture unnecessarily.

Other frequent causes outside the engine

Dragging brakes.
Poor alignment or suspension.
A slipping clutch.
Oil of unsuitable viscosity.

Guide table

Associated symptom	Possible cause
High consumption and black smoke	Injectors, air filter, turbo, EGR
High consumption and lack of power	Filters, turbo, pump or injector delivery
High consumption with frequent regenerations	Loaded DPF, excess soot
Consumption that rises gradually	Worn injectors, old filters, tires
Sudden rise in consumption	Fuel leak, failed injector, faulty sensor
Fuel smell	Leak in lines or injectors

How is it diagnosed?

Measure real consumption over several tanks.
Check the simple things: tires, filters, oil level, visible leaks.
Read fault codes and live data with a scan tool.
Test the injectors on a bench if the data points to the injection system.
Check the turbo, EGR and DPF if there are associated symptoms.

How to keep consumption reasonable

Keep filters and oil up to date. See diesel engine maintenance guide.
Check tire pressure regularly.
Deal early with symptoms of smoke or loss of power.
Avoid unnecessarily aggressive driving.

Frequently asked questions

Why is my diesel using more fuel than normal?+

It can be worn or leaking injectors, a clogged air or fuel filter, a leaking turbo, EGR or DPF problems, low tire pressure, extra load or a more aggressive driving style.

Do bad injectors increase fuel consumption?+

Yes. An injector that drips, has excessive return flow or sprays poorly uses more fuel and produces smoke. It is confirmed with a bench test.

How much should my diesel use?+

It depends on the vehicle, load and use. What is useful is knowing your own vehicle's usual consumption in similar conditions and watching for deviations.

Do additives reduce fuel consumption?+

Quality additives can help keep the system clean, but they do not correct wear or faults. If consumption has risen a lot, the cause has to be diagnosed.

Diesel Universal technical team

Laboratorio Diesel Universal S.A.S. Diesel injection laboratory in Barrancabermeja, Colombia. It diagnoses and calibrates injection pumps, injectors and turbochargers on an electronic test bench.

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