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Diagnosis and Treatment of Cummins Engine Power Shortage

Oct. 24, 2019

1. Cummins engine power shortage and exhaust white smoke

Engine power shortage, exhaust pipe exhausts white smoke, generally due to late injection time. At this time, not only the high speed operation is poor, the acceleration is not sensitive, and the temperature is too high.


a. Fuel injection advance angle is too small.

b. Injector is poorly atomized.

c. Engine temperature is too low.

d. There is water in the cylinder.

e. There is water in diesel oil.

Diagnosis and treatment

a. Engine power shortage, exhaust pipe exhaust white smoke, first of all, put your hand on the muffler exhaust port, if there are water droplets on your hand, check whether this is any moisture in the diesel and the cylinder (according to the engine starting difficulty or can not start and exhaust white smoke fault for maintenance).

b. When the engine is just started, it exhausts white smoke. the cause is that the starting temperatureis too low and some of the diesel oil volatilized into steam, which is discharged directly without combustion. If the white smoke gradually disappears after the engine temperature rises, it is normal. If the engine starts with white smoke, and the black smoke appears after the temperature rises, it means that the cylinder pressure is insufficient. Although the compression ignition condition is improved, the diesel oil cannot be completely burned, so that the engine power is insufficient, and the cylinder pressure should be checked and repaired.

c. Engine powe is insufficient, exhaust pipe discharges off white smoke, usually caused by too small fuel injection advance angle. If the engine temperature is too high and the speed is slow, it can be considered that the injection time is too late. If this phenomenon occurs suddenly, most of the fuel injection pump shaft is rotated relative to the fuel injection pump gear, resulting in a small injection advance angle. The timing of the injection timing should be adjusted.

d. Finally, check the injector atomization quality and adjust the injector.

Cummins generator

2. Engine power shortage and exhaust black smoke

There are two kinds of phenomenon of engine power shortage, uneven rotation speed and exhaust pipe black smoke: one is continuous black smoke exhaust; the other is intermittent black smoke and the engine shakes.


Insufficient engine power and continuous black smoke are formed by the excessive fuel supply in most or all the cylinders of the engine, the imbalance of the mixture of fuel and air, severe oxygen deficiency during combustion, incomplete combustion of diesel oil, and the discharge of suspended free carbon with the exhaust gas. If the exhaust pipe is intermittently black smoke, accompanied by a "chug" sound, it means that the individual cylinders are not completely burned. The reasons are as follows:

a. The fuel injection pump is not debugged properly, resulting in excessive oil supply and incomplete combustion.

b. Most injectors have poor injection quality.

c. Oil supply is not correct.

d. The opening height of the intake valve is reduced and the opening time is delayed, resulting in insufficient intake.

e. The air filter element is too dirty or the air filter is installed incorrectly, making the air is not smooth.

f. The supercharging efficiency of the supercharger decreases.

g. Poor fuel quality.

Diagnosis and treatment

When diagnosing such faults, it is important to proceed from the most obvious fault characteristics, whether continuous or intermittent black smoke, this principle should be followed.

a. If the engine suddenly emits black smoke, but the fault naturally disappears after running for a period of time, it is mostly caused by poor fuel quality. Because the impurities in the oil block the injector, the injection quality is poor, and the exhaust emits black smoke. After running for a period of time, Impurities are washed away by high pressure oil and this type of failure is not treated.

b. If black smoke is continuously discharged, it may be considered to check whether the intake air is unobstructed, and whether the intake pipe is deformed increases the intake resistance. First remove the air filter cover, take out the filter element and clean it, then re-test the machine to see if the exhaust pipe continues to exhaust black smoke. If the smoke exhaust is significantly reduced, it means that the air filter is too dirty or has a problem with the installation, which affects the intake air volume, the maintenance of the intake system should be strengthened.

c. If the air flow in the air inlet is unobstructed, it should be checked whether the oil supply time is too late. If the oil supply is too late, the fuel entering the cylinder will not be fully burned and will be discharged to form black smoke.

d. The injection quality of most injectors is seriously deteriorated, the fuel atomization is poor, can not adapt to the needs of combustion chamber shape, resulting in the formation of combustible mixture is difficult, and some of the fuel is converted into free carbon and discharged. This is also one of the causes of black smoke, so the injector should also be inspected and repaired.

e. Check that the fuel quality is up to standard and use standard diesel that meets the normal operation of the engine at ambient temperatures in the area.

f. Check that the supercharger is working properly. When the supercharger fails, the pressure at the end of the engine intake decreases, causing the temperature and pressure at the end of the compression to decrease, affecting fuel injection atomization and combustion temperature.

g. If the fuel injection pump is not repaired for a long time, the exhaust pipe is black smoke, and the power is insufficient, then it should be considered whether the fuel pump is improperly debugged to make the fuel supply too much. The fuel supply of the fuel pump under various working conditions should be recalibrated t o make it comply with the regulations.

h. If all of the above are normal and the engine has been running for a long time, consider checking that the valve opening height and opening time are correct. Long-term use can cause the valve transmission parts to wear, the normal valve phase and valve lift misalignment, the intake air amount is reduced, and the residual exhaust gas volume in the cylinder is correspondingly increased, which directly affects the full combustion of the fuel.

i. For uneven speed and intermittent exhaust of black smoke, engine weakness diagnosis can be checked by cylinder-by-cylinder oil cut-off method.

When a cylinder is cut off, the engine speed is significantly reduced, the black smoke is reduced, and the abnormal noise also disappears. This indicates that the cylinder supply of oil is too much, and the fuel injection amount of the cylinder should be checked and adjusted. If the engine speed changes little and the black smoke disappears, it indicates that the injector has poor spray quality, and the injector should be inspected and repaired. If the engine speed remains unchanged, it means that the cylinder does not work. The high pressure oil supply condition of the cylinder should be checked. For example, the fitting condition of the fuel pump plunger pair and the oil outlet valve pair, the fork is fixed on the oil quantity adjusting rod. Whether the screw (or the fastening screw of the ring gear) is loose, and the plunger spring is not broken. If it is normal, check the working condition of the injector and whether the cylinder has a mechanical failure.

Cummins diesel generator

3. Engine power shortage and exhaust blue smoke

The engine emits blue smoke at low temperature or small load, and becomes dark gray smoke after the temperature rises, and the power is insufficient.


When the engine is running, exhaust pipe discharges blue smoke, because the oil enters the combustion chamber, and when the engine is at low temperature or small load, it fails to burn and is discharged as blue smoke. However, when the engine temperature rises or the load increases, the oil vapor is burned and dark gray smoke appears. The reasons for the above phenomenon are:

a. Air intake is not smooth, causing the oil in the supercharger to be sucked into the cylinder to burn.

b. There is too much oil in the oil sump and the oil exceeds the maximum limit.

c. Oil enters the valve guide.

d. Cylinder is heavily bleeding oil.

e. The supercharger rotor shaft is seriously worn and the oil retaining ring is damaged, causing the supercharger to fail to reach the rated speed and oil leakage.

Diagnosis and treatment

a. Check that the air intake is unblocked and check whether there is oil in the supercharger housing.

b. Take out the oil dipstick after the engine is turned off for 5 minutes, and check whether the oil in the oil pan exceeds the maximum limit; if it exceeds, the excess part should be released.

c. If the above inspection is normal, the injector can be removed, check whether the nozzle hole of the needle valve is unobstructed. If the carbon deposit is serious or oily, the organic oil in the cylinder is intruded.

d. Check the upper end of the valve guide oil seal and the gap between the valve and the valve stem is too large. Further, the cylinder head should be removed to check whether the piston ring is stuck in the ring groove, the end gap is opposite, the fracture is weak, the elastic force is weakened, the conical ring or the twist ring is reversed, and the piston, the piston ring and the cylinder are worn excessively. No pull cylinders and other phenomena, if there are abnormal conditions, timely maintenance.

e. Whether oil leakage caused by improper use and improper maintenance of the turbocharger rotor shaft oil seal, mixed into fresh air into the cylinder, or vaporized by high temperature exhaust gas when exhausted from the turbine end with the exhaust gas. If the oil leakage should be replaced, the turbine carbon should be removed and the bearing clearance of the rotor shaft should be checked to avoid damage to the new oil seal.

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