Abnormal Fuel Consumption in Urban Buses Is Initially Linked to Injector Over-Fuelling, While a Lithuanian Fleet Uses Sensor Plausibility and Cylinder Correction Data to Avoid Misdiagnosis

Fuel-Consumption Changes Require More Than Injector Testing

A Lithuanian urban bus fleet noticed that several vehicles were using more fuel on comparable routes. Drivers did not report severe power loss, and no consistent injector fault code was stored.

Because excessive injector delivery can increase fuel consumption, the maintenance team initially considered removing the common-rail injectors. Before doing so, it reviewed sensor plausibility, ECU operating data, route conditions, and cylinder correction values.

The analysis showed why fuel consumption should not be used as a direct diagnosis of injector over-fuelling.

How Sensor Errors Can Change Fuel Control

The ECU calculates fuel delivery using information from multiple sensors. Incorrect but believable signals may not always trigger a fault code.

Relevant inputs include:

• Coolant temperature;
• Intake-air temperature;
• Fuel temperature;
• Boost pressure;
• Airflow;
• Exhaust temperature;
• Accelerator request;
• Vehicle speed;
• Ambient pressure.

For example, a coolant-temperature sensor reading lower than actual engine temperature may influence warm-up fuelling, idle strategy, fan operation, or after-treatment control.

Reviewing Sensor Plausibility

Cold-Start Comparison

Before the engine was started, coolant, intake-air, and fuel temperatures were compared with ambient conditions. One bus showed a coolant reading that differed from the other temperature sensors even though the engine had remained parked overnight.

Warm Operating Data

The sensor was then monitored during warm-up. Its value changed slowly and remained below an independently measured temperature.

The signal stayed within a technically possible range, explaining why the ECU did not store a clear circuit code.

Using Cylinder Correction Data Correctly

Injector correction values were reviewed at warm idle and under light load. No cylinder showed a persistent correction pattern indicating clear over-fuelling or under-delivery.

Correction values were not treated as direct flow measurements. They can also be affected by:

• Compression differences;
• Valve condition;
• EGR distribution;
• Sensor errors;
• Engine mounts;
• Electrical injector control.

Because the values remained balanced, immediate injector removal was not supported.

Checking Operating and Route Variables

The fleet also reviewed:

• Passenger load;
• Idling time;
• Heating and air-conditioning demand;
• Traffic conditions;
• DPF regeneration history;
• Tyre pressure;
• Route elevation;
• Driver operating patterns.

Fuel-consumption comparison was limited to buses with similar duty cycles.

Injector Selection Guidance

If testing later identifies a defective bus injector, the replacement should be confirmed using:

• Complete OE number;
• Engine serial number;
• Emissions stage;
• Power configuration;
• Calibration-code format;
• Fuel-system manufacturer.

A general bus model is not sufficient because engines and emissions systems may differ by production batch.

Industry Interpretation

The temperature-sensor problem was corrected before injector replacement was considered. Subsequent operating records were compared under similar route conditions.

The case illustrates a broader maintenance principle: abnormal fuel consumption is an operating result, not a component diagnosis.

Lithuanian bus fleets should combine sensor plausibility, cylinder correction, air-system data, regeneration history, and route information before concluding that diesel injectors are delivering excessive fuel.