What Causes a Vehicle to Overspeed?
2 Answers
Vehicle overspeeding can be attributed to the following reasons: 1. Fuel injection pump, governor: The fuel regulating rack and governor lever become detached. The plunger spring breaks or the plunger gets stuck in the high-speed position. The plunger's fuel adjustment gear ring fixing screw loosens, causing the plunger to lose control. Improper adjustment of the governor's high-speed regulating screw or maximum fuel supply. Excessive, overly viscous, or dirty lubricating oil inside the governor, or winter oil congealing, preventing the flyweights from opening. 2. Additional fuel entering the combustion chamber: Oil leaks into the cylinder, allowing engine oil to enter the combustion chamber and burn. The inertia oil-bath air cleaner holds too much oil, which is sucked into the combustion chamber and burned. In diesel engines with turbochargers, the turbocharger oil seal fails, allowing engine oil to enter the combustion chamber and burn. The electromagnetic valve of the cold start device leaks, allowing excess diesel to enter the combustion chamber and burn.
Back when I worked as an auto mechanic, I frequently dealt with runaway engine issues. The most common causes were stuck throttles or jammed throttle cables—like when sand, debris, or aging components prevent the pedal from returning, leaving the engine revving uncontrollably. Cracks or loose fittings in the intake system can also lead to runaway conditions by allowing unmetered air to disrupt the air-fuel mixture. This is especially critical in diesel engines, where a failed governor can’t regulate RPMs, or a stuck injector dumping excess fuel can trigger the same problem. In modern electronically controlled vehicles, faulty sensors (e.g., throttle position sensors) sending incorrect signals may cause the engine to surge. If it happens, prioritize safety: immediately turn off the ignition, engage the handbrake to slow down, and never try to tough it out. Post-incident fixes typically involve replacing parts or sealing leaks. Regular maintenance—like inspecting fuel lines and intake ducts—is key. Don’t cut corners on small expenses to avoid major roadside disasters.
