(English)
Contacts
1. Crankshaft speed is too low
During starting, the crankshaft rotates slowly and fails to reach the minimum speed required by the starter (typically over 100 rpm). In this case, check primarily whether the battery has sufficient charge, if the terminals are oxidized or corroded, if the starter is worn out or the brushes are worn, and whether the connections between the battery and the starter are loose or poorly contacting. Clean the terminals and tighten the bolts as necessary.
2. Cold start device required or present but non-functional
When ambient temperatures are low, diesel engines rely on auxiliary devices such as glow plugs, intake heaters, or cold-start fluids to ignite properly. If these devices are missing or installed but not functioning correctly (e.g., insufficient preheating time or burnt-out heating elements), the cylinder temperature at the end of compression will be too low. Verify the cold-start configuration required for this engine model and retest its functionality according to operating procedures to ensure it is working properly.
3. Poor-quality fuel
If the fuel contains excessive moisture, too many impurities, or is of incorrect grade, it can severely affect the combustion process, resulting in difficulty starting and white or black smoke from the exhaust pipe. In such cases, all poor-quality fuel should be completely drained from the fuel tank and entire fuel system. The fuel lines, filters, and fuel injection pump should be cleaned thoroughly, and high-quality, standard-compliant diesel should be refilled.
4. The fuel’s cloud point is higher than the ambient temperature
The cloud point refers to the temperature at which paraffin begins to precipitate and the diesel becomes cloudy. When the ambient temperature falls below the fuel’s cloud point, paraffin crystals can clog the fuel filter and fuel lines, causing poor fuel flow. In such cases, it is necessary to switch to low-cetane diesel suitable for current climatic conditions and simultaneously replace the fuel filter to remove any accumulated wax residue.
5. Clogged Air Filter
A clogged air filter significantly increases intake resistance, resulting in insufficient air entering the cylinders. This leads to low pressure and temperature at the end of compression, as well as a rich fuel mixture that fails to ignite. Remove the air filter element and inspect it for dirt accumulation. If excessive contamination is present or the filter paper is damaged, clean it thoroughly with compressed air from the inside out (depending on the type) or replace it with a new filter element.
6. Air in the fuel system
When the fuel line is not properly sealed or when air is not fully purged after replacing the filter, air may enter the high-pressure fuel line. This can result in insufficient opening pressure of the injector needle valve or intermittent and uneven fuel delivery, preventing effective combustion. To resolve this, loosen the bleed screws on the fuel filter and fuel pump, then manually operate the hand primer pump until fuel flows out without any bubbles. Once clear fuel is observed, tighten the bleed screws to ensure the entire fuel system is filled with fuel.
7. Incorrect fuel injection timing of the fuel injection pump
If the fuel injection timing is too early, the peak cylinder pressure occurs prematurely, reducing power efficiency and causing knocking sounds; if it is too late, combustion is delayed, resulting in white smoke from the exhaust and engine overheating. Use a timing light or refer to the flywheel scale and high-pressure fuel line pulsation method to check whether the fuel advance angle falls within the specified range for this engine model (typically 15° to 25°). Adjust the relative position between the fuel injection pump and the drive gear if it does not meet the requirements.
8. Incorrect valve clearance
If the valve clearance is too large, the valve will open late and have insufficient lift, resulting in reduced intake and exhaust efficiency and lower compression pressure. If the clearance is too small, the valve will not seal properly, causing gas leakage and similarly leading to inadequate pressure and temperature at the end of compression. Use a feeler gauge to measure each cylinder while the engine is cold, then readjust the clearance to the manufacturer-specified values for intake and exhaust valves (typically 0.25–0.35 mm). After adjustment, tighten the adjusting screw securely and recheck the clearance.
