A recycling plant reported a terrifying incident involving a TCM FD25T (Nissan QD32 diesel engine) forklift. The operator attempted to turn off the engine, but the engine continued to run roughly, emitting thick white smoke and shooting actual flames from the exhaust tailpipe. The key was removed, but the engine kept running (dieseling/runaway) until the air intake was physically blocked with a board to suffocate it.
The technician first investigated why the ignition couldn't kill the engine. He checked the "Fuel Shut-Off Solenoid" on the injection pump. When 12V was applied, the solenoid did not click. He removed the solenoid; the internal plunger was seized in the "Open" (run) position due to severe carbon and sludge buildup. Because the solenoid couldn't physically pull the fuel rack to the stop position, cutting the electrical power had no effect on the fuel supply.
However, the flames and white smoke indicated the engine was burning something other than just diesel. He checked the engine oil dipstick. The oil level was over 40 mm above the "FULL" mark. The operator had mistakenly added 4 extra liters of oil. The crankcase was so overfilled that the crankshaft counterweights were dipping into the oil, whipping it into a froth. The excess liquid oil was forced up through the "Positive Crankcase Ventilation (PCV)" system directly into the intake manifold.
The engine was running on a mixture of injected diesel and ingested engine oil. The engine oil has a very high flash point and burns slowly, which is why it was exiting the combustion chamber unburnt (white smoke) and igniting in the hot exhaust manifold (flames). The combination of uncontrolled fuel (seized solenoid) and the secondary fuel source (ingested oil) caused the runaway condition.
The repair involved completely draining the excess engine oil and refilling to the correct level. The intake manifold and cylinder head ports were cleaned of heavy oil sludge. The seized fuel shut-off solenoid was replaced, and the injection pump fuel rack was freed up to move smoothly. The engine was then run with a heavy-load dyno test, burning off the residual oil in the cylinders. The exhaust cleared, and the engine shut off cleanly via the key.
