Mining Haul Trucks Supply Fuel Normally When Cold but Gradually Lose Power Under Sustained Load Despite New Injectors: A Mali Workshop Uses Hot Fuel-Supply Pressure, Flow Comparison and Internal Bypass Checks to Identify a Low-Pressure Transfer-Pump Fault

Why the Problem Appeared to Be Injector-Related

A mining maintenance team in Mali investigated a haul truck that started normally and produced acceptable engine response during the first part of each shift. After prolonged loaded operation, however, the truck gradually lost pulling power. Reducing engine load allowed partial recovery, but the symptom returned when the vehicle resumed sustained hauling.

Because the engine showed fuel-pressure-related symptoms, the diesel injectors were initially suspected. A replacement injector set did not materially change the operating pattern.

That result shifted the investigation upstream. The independent technical core became temperature-dependent loss of low-pressure transfer-pump capacity.

Cold Tests Created a Misleading Picture

The Mali workshop first measured low-pressure fuel supply shortly after engine startup. Supply pressure appeared suitable for normal operation, and no obvious external fuel leakage was found.

The difficulty was that the original complaint did not occur cold.

Technicians therefore recorded fuel-system behaviour through a longer operating cycle representative of haulage at the Mali mining site.

As the engine and fuel system warmed, they compared:

• Transfer-pump inlet condition;
• Pump outlet pressure;
• Fuel flow under increasing demand;
• Filter restriction;
• High-pressure rail response.

The important change occurred on the low-pressure side.

Pressure Before and After the Pump Told Different Stories

Fuel remained available at the pump inlet, but outlet performance deteriorated as operating temperature increased.

This reduced the amount of fuel available to the high-pressure pump during heavy demand.

The common-rail system could therefore show pressure difficulty even though the injectors were not creating excessive leakage.

Internal Bypass Became the Main Direction

A transfer pump may contain internal clearances, pressure-regulating components or bypass paths depending on its design.

When wear is present, temperature can alter how effectively the pump maintains delivery.

The Mali technicians evaluated the pump according to the applicable system procedure rather than assuming that a pump capable of producing pressure when cold was healthy under all conditions.

The comparison between cold and hot output provided the key evidence.

The investigation also checked the tank pickup, suction hoses and filters to make sure the pump was not simply reacting to an upstream restriction.

Mining Duty Made Thermal Testing Essential

At the workshop, the truck could idle for long periods without reproducing the complaint. At the Mali mine, it operated under sustained engine load while hauling material, creating significantly different fuel demand and thermal conditions.

This distinction changed the test strategy.

Instead of relying on a short static pressure reading, technicians evaluated the truck after the fuel system reached the temperature associated with the actual failure.

That prevented another set of diesel fuel injectors from being removed unnecessarily.

Corrective Work and Verification

After the low-pressure pump issue was addressed, the workshop repeated the same loaded operating cycle.

Supply pressure and flow were monitored from cold operation through the hot condition that had previously caused power loss.

The pressure deterioration was no longer reproduced in the same way, and the high-pressure system was able to follow engine demand more coherently.

Technical Interpretation

The main lesson from this Mali mining case is that fuel supply capacity must be evaluated at the temperature and load where the complaint occurs.

A transfer pump can appear functional during cold idle testing yet fail to maintain adequate delivery after prolonged operation.

When new injectors do not change a whole-engine power-loss condition, comparing pump inlet and outlet behaviour under hot load can distinguish an injector problem from an upstream supply fault.