A sand and gravel operation reported that a Komatsu WA380-8 wheel loader was generating thick black smoke under load and lacked the power to climb the stockpile ramp with a full bucket. The engine idled smoothly, but the moment the bucket was driven into the aggregate pile, the exhaust stack would belch soot and the machine would struggle to maintain forward momentum. The engine RPM did not flare, suggesting a lack of air rather than a transmission slip.
Because the black smoke indicated an unburned fuel condition (too much fuel, not enough air), the technician checked the turbocharger. A boost gauge was teed into the intake manifold. Under full load, the turbo was only generating 9 psi of boost, far below the specified 24 psi. The turbocharger actuator and wastegate lever were checked. The wastegate lever was found seized in the fully open position due to rust and carbon buildup on the pivot pin. With the wastegate stuck open, exhaust gases bypassed the turbine, preventing the turbo from spooling up and generating boost.
However, the lack of boost did not fully explain the severity of the black smoke. The technician traced the intake tract from the turbocharger compressor outlet to the engine intake manifold. The WA380 utilizes an air-to-air Charge Air Cooler (CAC) mounted in front of the main engine radiator. The rubber boost hose connecting the CAC to the intake manifold was soaked in oil, and upon closer inspection, the aluminum core of the CAC had split along a horizontal weld seam.
The split core allowed the limited compressed air from the sluggish turbo to vent directly to the atmosphere. The engine's mass airflow sensor read the lack of incoming air, but the ECM overcompensated by dumping fuel, resulting in the black smoke and sluggish performance. The crack in the CAC was caused by severe vibration fatigue, as a broken mounting bracket had allowed the cooler to resonate against the frame.
The repair involved freeing the seized wastegate lever, lubricating the pivot with high-temperature anti-seize, and replacing the damaged charge air cooler and its mounting bracket. The entire intake tract was chemically cleaned to remove the oily sludge. After reinstalling the components, the loader achieved 25 psi of boost under load, the black smoke disappeared completely, and the bucket sliced through the aggregate with full breakout force.
