New High Quality Diesel Injector 386-1753 20R-1265 386-1754 20R-1266 386-1758 20R-1270 386-1760 20R-1272 For CAT C3500B

1. Pressure is lower than the standard value
Possible causes and solutions
Failure of the pressure regulating mechanism
Weak or broken pressure regulating spring
Solution: Disassemble the injector and replace the same type of pressure regulating spring (adjust the preload according to the manual, such as controlling the opening pressure by the thickness of the gasket).
Example: The standard opening pressure of a mechanical injector is 12MPa. The spring is weak and the actual pressure is 8MPa. After replacing the spring, it returns to normal.
The valve core is stuck in the pressure relief position
Solution: Soak the valve core components (such as needle valve pairs) with diesel, clean the carbon deposits and colloid with a soft brush, and apply a small amount of lubricating oil before assembly to test the sliding flexibility.
Note: If the wear is severe (such as scratches), the needle valve pair needs to be replaced as a whole.
Insufficient fuel supply
Low-pressure oil circuit is blocked
Solution: Check the fuel filter and the oil pump filter, replace the blocked filter element; clean the sediment at the bottom of the fuel tank (compressed air can be used to blow back the pipeline).
High-pressure pump wear
Solution: Check the oil supply capacity of the high-pressure pump (such as the wear of the common rail pump plunger leading to insufficient rail pressure), and professional equipment is required to repair or replace the high-pressure pump.
Poor injector seal
Wear of the needle valve sealing surface
Solution: Use grinding paste to manually grind the sealing surface (clockwise/counterclockwise rotation for about 20-30 times) until the contact surface forms a uniform bright ring; if grinding is ineffective, replace the pair.
O-ring aging and oil leakage
Solution: Replace the O-ring of the same specification (pay attention to the installation position, such as the tail seal of the common rail injector), and apply a small amount of engine oil to prevent damage during installation.

2. Pressure is higher than the standard value
Possible causes and treatment methods
Abnormal pressure regulating mechanism
Excessive spring preload
Solution: Disassemble the injector, reduce the thickness of the pressure regulating spring gasket (such as the original gasket thickness of 1.2mm, it can be replaced with 0.8mm), and retest the opening pressure to the standard value.
The valve core is stuck in the closed position
Solution: Clean the valve core and valve seat, and check whether there are foreign objects (such as metal debris) stuck; if the sticking is caused by high temperature deformation, the parts need to be replaced.
Failure of electronic control components (common rail system)
Pressure control solenoid valve (PCV) stuck
Solution: Use a multimeter to detect the resistance of the solenoid valve (standard value 1-3Ω), if the resistance is abnormal, replace the solenoid valve; if the resistance is normal but the signal is abnormal, check the ECU output voltage (about 2-3V pulse at idle speed).
Rail pressure sensor false alarm
Solution: Use a diagnostic instrument to read the sensor data stream, compare the actual pressure gauge value (such as the sensor shows 150MPa but the actual measurement is 100MPa), replace the sensor and recalibrate.
Oil return line is blocked
Oil return pipe is bent or the filter element is blocked
Solution: Clear the oil return line, replace the blocked oil return filter element (some models need to pass through an independent filter for oil return), ensure smooth oil return and reduce back pressure.

3. Severe pressure fluctuations
Possible causes and solutions
Air mixed in the fuel
Low-pressure oil circuit leaks
Solution: Before starting the engine, use a manual pump to pressurize to 2MPa and observe whether the pressure gauge continues to drop (if it drops by >0.5MPa per minute, it is leaking); focus on checking the oil pipe joints and oil pump seals, and replace damaged parts.
Intermittent failure of the solenoid valve
Poor contact of the common rail pressure control solenoid valve
Solution: Use an oscilloscope to monitor the solenoid valve drive signal. If the pulse waveform is intermittent or missing, check whether the line plug is loose and whether the pins are oxidized; repair the line or replace the solenoid valve.
Fuel injector needle valve jumps
Uneven spring elasticity or uneven valve seat wear
Solution: Disassemble the fuel injector and check the verticality of the spring (deviation >1mm needs to be replaced); when the valve seat wears and causes the needle valve to tilt, the valve seat needs to be ground or the pair replaced.
4. Special fault handling of electronic common rail system
ECU control strategy abnormality
Solution: Use diagnostic instrument to read fault code (such as P0087 - rail pressure is too low). If it is an occasional fault, try to clear the code and then conduct a road test; if it persists, check whether the ECU power supply (12V normal power and 5V sensor power supply) and grounding are reliable.
The pressure limiting valve opens frequently
Reason: The rail pressure exceeds the safety value (such as more than 200MPa), and the pressure limiting valve releases pressure, causing a sudden drop in pressure.
Solution: Check the command duty cycle of the pressure control solenoid valve (full load should be more than 80%). If the duty cycle is insufficient but the rail pressure is too high, the solenoid valve core may be worn and the assembly needs to be replaced.

5. Verification steps after maintenance
Pressure retest
Mechanical injector: Retest the opening pressure and sealing (such as the opening pressure error ≤±5%, the pressure drop within 30 seconds <0.3MPa).
Common rail system: Use diagnostic instrument to monitor rail pressure fluctuation during road test (idle fluctuation ≤±2MPa, response delay during acceleration <0.5 seconds).
Engine running test
Observe starting performance: Normally, it should start within 2-3 seconds, without starting difficulty or idle jitter.
Detect exhaust smoke color: When the pressure is normal, the exhaust gas should be colorless or light gray; if the pressure is too low, black smoke may be emitted (incomplete combustion), and if the pressure is too high, blue smoke may be emitted (engine oil participates in combustion).
Data comparison
Record the corresponding relationship between pressure data, injection volume and engine speed before and after maintenance to ensure that it meets the manufacturer's standards (for example, the rail pressure of a certain model should be 130±5MPa at 2000rpm).

6. Preventive measures
Regular maintenance
Replace the fuel filter (including oil-water separator) every 5000-10000 kilometers to prevent impurities from entering the injector.
Check the sealing of the low-pressure oil circuit every year, focusing on the aging of the rubber pipeline (it is recommended to replace the fuel hose of the entire vehicle every 3 years).
Use qualified fuel
Avoid using diesel with too high sulfur content (national VI sulfur content ≤ 10ppm) to prevent valve core corrosion and common rail system wear.
Professional operation
When disassembling the common rail injector, it must be done in a clean environment (such as using a dust-free workshop) to avoid dust entering the gap between precision parts.