A site contractor reported that a JCB JS220 excavator would suddenly lose power and stall when digging in hard clay. The engine would restart immediately but would run rough, with the check engine light flashing. The problem was intermittent, happening only when the hydraulic system reached peak pressure.
The technician connected JCB's diagnostic software and retrieved a fault code for "Camshaft Position Sensor Signal Plausibility" and "Injector Circuit Fault." Initially, the camshaft sensor was replaced, but the stalling persisted. The technician then focused on the injector harness.
On the JS220, the main engine harness runs close to the high-pressure fuel pump. Over time, engine vibration had caused the wiring loom to rub against the fuel pump bracket. Upon inspection, the plastic conduit was worn through, exposing the copper wires of the injector signal cables. When the excavator dug into hard clay, the engine torque caused the engine to rock on its mounts. This movement forced the exposed injector wires to ground against the metal bracket, shorting the circuit. The ECU detected the short and cut fuel to the cylinders, causing the stall.
The camshaft sensor fault was a red herring caused by the electrical noise generated by the shorting injector wires. The ECU was receiving conflicting signals and could not determine the precise crank angle.
The repair involved repairing the chafed wires with solder and heat-shrink tubing. The harness was then re-routed and secured away from the fuel pump bracket, with a protective abrasion sleeve installed. The battery was disconnected to reset the ECU adaptive learning. After the repair, the excavator was put under a full stall test, and the engine held steady RPM with no power loss or fault codes.
