What Causes Diesel Engine Runaway in Vehicles?
3 Answers
Diesel engine runaway in vehicles can be caused by the following reasons: Excessive Fuel Supply: The plunger remains at the maximum fuel supply position, and the governor fails to regulate, leading to increased engine speed. The governor cannot control the fuel quantity, the fuel rack and pinion may lack alignment marks or be incorrectly installed, the plunger might be reversed, injection pressure could be too low, excessive fuel is supplied to the cylinders, the linkage may be stuck in the governor's moving parts, or worn injectors may allow excessive return fuel from the intake manifold to be drawn into the cylinders, resulting in over-fueling. Solution: Excessive diesel fuel supply causing runaway is often indicated by thick black smoke from the exhaust pipe. Inspect components of the fuel supply system, such as the fuel pump, injectors, and governor, and perform necessary repairs after analysis. Oil Burning: Excessive clearance between the piston and cylinder wall causes oil to splash into the combustion chamber during piston movement. If the oil viscosity is too low, lubrication effectiveness decreases, accelerating piston ring wear. A blocked crankcase ventilation port increases oil pressure and return resistance. Aging or failed valve stem seals allow oil to enter the combustion chamber through the gap between the valve stem and guide hole under intake manifold vacuum, leading to oil combustion. Solution: Oil entering the combustion chamber is typically indicated by blue smoke from the exhaust pipe. Check the lubrication system components to determine if the oil level is too high or if the oil does not meet specifications.
Having driven diesel vehicles for over 20 years, I can attest that diesel engine runaway is truly terrifying—once the RPM spirals out of control, the engine is as good as ruined. Common causes include: 1) A failed governor, the small component meant to regulate fuel injection for stable operation. If worn out or with a broken spring, it floods the engine with fuel unchecked. 2) Excessive fuel supply due to issues like a leaking injection pump/fuel line, stuck pistons, or clogged diesel filters causing sudden pressure spikes. 3) Uncontrolled air intake from leaks in the intake manifold or turbocharger malfunctions, where excess air intensifies combustion. Additionally, engine oil seeping into the combustion chamber (mixed burning) or lubrication failures can also trigger this. If it happens, act fast—cut throttle or block the air intake to force shutdown, then seek immediate repair. Prevention-wise, regular diesel system maintenance is critical to avoid catastrophic runaway incidents.
I'm super interested in diesel engines. From my experience with modified cars, there are several reasons for engine runaway: First, the governor fails to function, either due to aging or the throttle linkage getting stuck. When you step on the accelerator, the fuel supply skyrockets uncontrollably. Second, excessive fuel delivery caused by a malfunctioning high-pressure fuel pump or injectors spraying too much fuel. Then there's the issue of air leaks, such as poor cylinder sealing, where air leakage actually promotes combustion. Also, accidental mixing of engine oil, like when oil seals break and lubricating oil enters the combustion chamber, causing the RPM to surge wildly. The danger lies in the vehicle going out of control, potentially damaging the engine or even causing an explosion. My suggestion is to regularly use diesel additives to clean carbon deposits and inspect the fuel system weekly. If you encounter engine runaway, shut off the engine immediately without hesitation—safety first.
