Causes of starting faults in construction crane engines: 1. Fuel quality does not meet specifications or is too poor; 2. Fuel pressure is too low; 3. Incorrect engine valve clearance; 4. One cylinder of the engine is not working; 5. Incorrect injection timing or incorrect fuel quantity setting; 6. Air leakage in the intake system; 7. Faults in the brake and its control lever; 8. Carbon deposits in the turbocharger.

　　Troubleshoot step by step from simple to complex: first check whether the fuel is qualified and use qualified fuel; check whether all engine cylinders are working normally; after inspection, all cylinders were found to be working normally; check whether the fuel pressure is too low, whether the return fuel volume is too large, and whether the return valve pressure is sufficient, so check the return valve; check the valve clearance and adjust the intake and exhaust valve clearance according to the allowable range for the valve clearance of the relevant construction crane engine; then adjust the injection timing and fuel quantity according to the machine's injection timing and fuel quantity setting instructions.

　　After completing the above checks, test the machine again. It was found that when operating in gears i-iii, the exhaust smoke was normal, but the speed and pump pressure were both low. When operating in gear iii, the brake did not move. After using the manual throttle control linkage to add fuel, the engine speed and main pump pressure both increased somewhat, but black smoke appeared. The black smoke may have been caused by uneven fuel addition when using the manual throttle control linkage to add fuel.

　　Then check the brake again. First, check the electrical circuit of the brake; the result was normal. Disassemble the brake and found dirt accumulated inside. Inspect and clean all components, install the inspected brake, and test the machine again. It was found that the fault symptoms were somewhat reduced.

　　Then replace it with a new brake and test the machine to observe the working conditions in each gear. The engine speed, pump pressure, and exhaust smoke were all normal.