The Most Common Symptoms of Engine Malfunctions And How To Diagnose Them

Long term use of the engine can cause various faults such as power, noise, fuel consumption, and idle speed, and most of these problems have obvious external symptoms. Mastering common fault manifestations and basic diagnostic logic can quickly locate problems and avoid blind replacement and excessive maintenance.

1、 Idle shaking fault and diagnosis

Unstable idle, body shaking, and large speed fluctuations are the most common faults. The main causes are excessive carbon deposition, aging spark plugs, poor fuel atomization, and sensor data deviation. Diagnosis prioritizes visual inspection of throttle carbon deposits, detection of spark plug clearance and erosion, reading of computer data streams, observation of fuel injection correction and intake pressure values, and troubleshooting of cylinder deficiency and mixture imbalance issues.

2、 Power weakness, increased fuel consumption, and diagnosis

Slow acceleration, sluggish acceleration, and abnormally high fuel consumption are mostly caused by a decrease in combustion efficiency. Common reasons include clogged air filters, insufficient ignition energy, dirty fuel injectors, and clogged three-way catalytic converters. Firstly, check the status of the intake and filter element, test the ignition condition, check the fuel pressure, and finally troubleshoot the exhaust blockage layer by layer.

3、 Engine abnormal noise fault and diagnosis

Common abnormal noises are divided into clattering valve sounds, clattering timing sounds, and dull knocking cylinder sounds. Cold start abnormal noise is mostly caused by the release of pressure from the timing tensioner and hydraulic tappet; The continuous metal abnormal noise of a hot car is mostly caused by the wear of internal bearings and pistons. Diagnosis relies on comparing hot and cold cars, listening to changes in engine speed, and combining disassembly of accessory belts and no-load testing to distinguish between external accessory noise and internal mechanical noise of the engine.

4、 Diagnosis of oil burning and leakage faults

Blue smoke from the exhaust pipe and rapid decrease in oil level are symptoms of burning oil; There is oil sludge and joint oil leakage around the machine, indicating a sealing failure. Firstly, diagnose the external oil seal and valve cover oil leakage, then determine the cold car blue smoke (valve oil seal) and hot car blue smoke (piston ring wear), distinguish between external leakage and internal burning, and avoid misjudging major repairs.

5、 Fault light on diagnosis

The engine malfunction light is always on, mostly due to abnormal sensors, oil circuits, and ignition systems. Prioritize reading fault codes to lock in the fault range, and verify the working status of sensors through data flow. Do not blindly replace parts, and determine whether it is a damaged part, carbon deposition, or wiring problem through data comparison.

In summary, engine diagnosis follows the principles of "external first, internal second", "simple first, complex second", and "data first, disassembly second". By corresponding symptoms to faults and conducting layer by layer troubleshooting, it can accurately repair vehicles and significantly reduce maintenance costs.