What is the reason for the humming sound when accelerating in fourth gear of Wuling Zhiguang?

[SanKinsley]

The reasons for the humming sound when accelerating in fourth gear of Wuling Zhiguang are as follows: 1. Engine fuel pump malfunction: Damage to the engine fuel pump results in insufficient fuel supply. Even if the driver floors the accelerator, causing the engine speed to increase, the fuel injection volume remains low, leading to reduced engine output power and consequently weak acceleration. 2. Valve timing issue: Modern engines utilize CVVD valve timing systems to improve fuel efficiency. However, if the CVVD hydraulic control system is damaged, with oil leaks from sealing rings or malfunctioning CVVT, the engine's intake and exhaust will be affected, naturally reducing combustion efficiency and causing a drop in engine output torque.