If the diesel engine is difficult to start, it indicates that although diesel can enter the combustion chamber, for some reason the combustion chamber does not have the conditions for compression ignition, causing the injected diesel to not burn or not burn completely. A large amount of black smoke emission is mostly caused by reasons such as intake passage blockage, early fuel injection, insufficient injection pressure, poor atomization, low cylinder pressure, poor diesel quality, or excessive fuel supply.

　　

 

　　Fault Phenomenon 1

　　After turning on the starter switch, a large amount of black smoke is emitted from the exhaust pipe, but the engine cannot start.

 

　　Fault Causes

　　a. The fixing bolts on the fuel injection pump drive coupling are loose, or the fuel injection timing is adjusted too early.

　　b. Fuel injection pump failure, such as severe wear of the fuel injection pump plunger, push rod, or cam, or loose adjustment screws of the plunger push rod.

　　c. Fuel injector failure, such as the injector needle valve sticking and unable to close, poor contact or leakage between the needle valve and valve seat, or loose adjustment screws of the injection pressure spring.

　　d. In the case of wear of the fuel injection pump plunger pair, improper governor adjustment causes excessive fuel supply.

　　e. Low cylinder pressure.

　　f. Air filter and intake passage blockage.

　　g. Exhaust brake valve not fully opened.

　

　　Fault Diagnosis

　　a. First check whether the intake and exhaust passages are unobstructed, such as whether the air filter is blocked, whether the intake hose is collapsed or its inner wall is delaminated and blocked, and whether the exhaust brake is fully opened.

　　b. If the engine has knocking sounds and emits black smoke, it indicates that the fuel injection timing is too early and should be readjusted. Usually, this situation is caused by loose screws on the fuel injection pump coupling, damaged shaft keys, or misaligned drive plates. If no problems are found, check the fuel injection timing as follows: remove the high-pressure oil pipe of the first cylinder, so that the oil level in the center hole of the fuel injection system outlet valve pressing seat is clearly visible, place the fuel supply rack in the supply position, pump air out of the oil circuit from the vent screw, slowly rotate the crankshaft, carefully observe the changes in the oil pump outlet valve liquid level; as long as the liquid level changes, it indicates fuel supply has started, immediately stop rotating the crankshaft and check whether the fuel injection advance angle is correct. At this time, the timing mark on the fuel injection pump coupling plate should coincide with the mark on the pump body.

　　c. If all the above checks are normal, check the atomization condition of the fuel injector. When the injector is tested on the test bench, its injection pressure, injection cone angle, and range should meet the standards; otherwise, disassemble and inspect whether the needle valve is stuck, whether the needle valve and seat are sealed, whether the injection pressure adjustment spring is too soft or broken, and whether there is carbon buildup on the injector seat gasket.

　　d. If the fuel supply system is all normal but the engine emits black smoke and cannot start, check the engine cylinder pressure. If the pressure is insufficient, find the cause from the valves, piston rings, and cylinder gasket.

 

　　The engine runs smoothly without high speed and emits very little smoke.

 

　　Fault Phenomenon 2

　　The engine lacks power, but ignition is still uniform, and the smoke emission is very low. Only during rapid acceleration is there a small amount of black smoke, but the high speed still cannot be reached.

 

　　Fault Causes

　　a. The throttle lever travel cannot guarantee the maximum fuel supply.

　　b. Improper governor adjustment cannot guarantee the maximum fuel supply of the fuel injection pump.

　　c. The fuel quantity adjustment rack of the fuel injection pump cannot reach the maximum fuel supply position.

　　d. The fuel injection pump push rod is sticky.

　　e. Excessive wear of the fuel injection pump push rod roller or cam.

　　f. The fuel injection pump plunger is sticky or its spring is broken.

　　g. Excessive wear of the fuel injection pump plunger.

　　h. Loose fixing screws of the fuel injection pump sector small gear.

　　i. Poor sealing of the fuel injection pump outlet valve.

　　j. Injector leakage reduces the fuel injection quantity.

　　k. Blockage of the fuel injection pump filter screen, oil pipe, or diesel filter.

　　l. High diesel viscosity causing poor flow.

　　m. Insufficient fuel supply from the fuel transfer pump.

　　n. Air in the fuel line.

　

　　Fault Diagnosis

　　From the fault phenomenon, it can be determined that the engine speed cannot increase because the maximum fuel supply is not obtained. During diagnosis, air should be removed from the fuel supply system first, then the following procedures should be followed for inspection.

　　a. Check the throttle lever travel. Press the throttle pedal to the bottom and move the fuel injection pump fuel quantity adjustment arm; if it can still be pushed in the fuel increase direction, it indicates that the throttle lever cannot make the fuel injection pump reach the maximum fuel supply and should be adjusted.

　　b. Check the fuel supply quantity. First, check and adjust the governor high-speed limit screw and the maximum fuel supply limit screw. Turning in the high-speed limit screw reduces the high speed, and turning it out increases it; turning in the maximum fuel supply limit screw increases the fuel supply, and turning it out decreases it. When both adjustment screws are turned in the increasing direction and the engine feels powerful, it indicates the problem is here. Adjust the fuel supply until black smoke is emitted from the exhaust pipe during rapid acceleration. Next, check the high-pressure oil circuit parts such as the fuel injection pump and governor. Remove the injector cover to see if the fuel quantity adjustment rack can reach the highest speed position, whether the fuel injection pump push rod or plunger is sticky, whether the plunger, push rod roller, and cam are excessively worn, whether the plunger spring is broken, and whether the outlet valve is sealed. If all are normal, check whether the injector leaks and whether the governor spring force meets the standard. If the fault is not in the high-pressure oil circuit, check the low-pressure oil circuit, mainly whether the fuel tank vent hole and pipeline are blocked, whether the fuel transfer pump filter screen is blocked, whether the diesel filter is blocked, whether the fuel transfer pump oil valve leaks or sticks, and whether the entire oil circuit leaks.

　　c. Check engine moving parts, such as pistons, crankshaft and connecting rod bearings, camshaft bearings, timing gears and idler gears for any sticking.

　　d. In cold seasons, also check whether the diesel fuel grade used meets the requirements.

　　

　　Engine runs unevenly, exhaust pipe emits black smoke.

 

　　Fault Phenomenon 3

　　Engine lacks power, runs unevenly and emits black smoke, knocking sound when accelerating.

　　

　　Fault Causes

　　a. Fuel injection pump failure, such as excessive wear of individual cam or pushrod rollers, improper or loose adjustment of pushrod adjusting screws, loose fixing screws of individual plunger sleeve sector gears, stuck plungers or broken springs, worn fuel delivery valves or broken springs, etc.

　　b. Injector failure, such as needle valve sticking and not closing, poor sealing of the injector needle valve, broken or weak pressure adjustment spring of the injector, carbon deposits on the injector sealing gasket, etc.

　　c. Cylinder pressure too low.

　

　　Fault Diagnosis

　　First, perform a cylinder-by-cylinder fuel cut-off test while the engine is running. When fuel is cut off from a cylinder, if the engine speed significantly decreases, black smoke reduces, and knocking sound weakens or disappears, it indicates that the cylinder is over-fueled; if the engine shows no or slight change, it indicates under-fueling; if engine speed changes little but black smoke disappears, it indicates poor atomization quality of the injector in that cylinder. After identifying the faulty cylinder, further check the cause of the fault, such as the condition of the fuel injection pump plunger pair, whether the sector gear fixing screws are loose, and whether the plunger spring is broken. If all are normal, the injector can be disassembled and inspected, and if necessary, replaced with a new injector for comparison. If the fault disappears with the new injector, it indicates the original injector is faulty.

　　Secondly, for fuel injection pump plungers with pushrods that have adjusting screws, check whether the fuel injection timing of each cylinder is consistent.

　　

　　If none of the above issues are found, test the pressure of the faulty cylinder to determine whether there is leakage due to wear of the cylinder, piston, piston rings, or poor valve sealing.

　　Source: Diesel Vehicle Service Club