Common Faults and Troubleshooting of Cummins Engine

by MOU YONG HONG on December 01, 2021

This article will guide you to understand the common faults and troubleshooting of the Cummins engine.

1. Diagnosis and treatment of engine starting difficulty or failure to start out and pipe emitting an outsized amount of ash and white smoke.

The engine is difficult to start outand therefore the pipe discharges an outsized amount of gray smoke, which is diesel vapor.

a. The engine temperature is just too low, diesel fuel isn't easy to evaporate and burn.
b. Poor atomization of injector
c. The oil supply is just too late.
d. The oil supply is just too small and therefore the mixture is just too lean.
e. Cylinder leakage is just too much, compression can't reach the ignition temperature.

Diagnosis and treatment
a. If the engine temperature is just too low in the cold season, check whether the coldness starting preheating device fails, that is, whether the preheater negative feedback circuit has a circuitshort, or preheater failure.
b. If the coldness preheating device is normal, check whether the injection timing is correct. Turn the engine and insert the engine camshaft timing pin, that is, when it's located at the upper dead center of cylinder compression, check whether the fuel pump camshaft lock pin is often inserted. If it can't be inserted, it indicates that the injection timing is wrong and wishes to be adjusted.
c. The spray quality of every cylinder injector should be checked to satisfy the wants.
d. If the primary two items are normal, check if the oil supply is just too small. During a cold start, thanks to the coldness within the cylinder, the fuel viscosity is large, and therefore the evaporation condition is poor, the starting oil supply is required to be larger than the rated oil supply.
e. Finally check the cylinder pressure and repair it when the pressure difference is extremely far.

2. Diagnosis and treatment of engine starting difficulty or failure to start out and pipe emitting tons of black smoke.

The engine is difficult to start outand therefore the pipe emits an outsized amount of black smoke, which is that the result of incomplete combustion of the diesel fuel.


a. diesel fuel is of poor quality.
b. The air intake isn't smooth and therefore the air cleaner is blocked.
c. The injection timing adjustment is just too early.
d. Injector needle valve sealing is poor, there's dripping oil leakage phenomenon.
e. The injection pressure is just too low
f. The fuel supply of the fuel injection system pump is just too large and therefore the combustion has deteriorated.
g. Low cylinder pressure and poor atomization.

Diagnosis and treatment
a. Determine if the diesel quality meets the wants.
b. Check if the air cleaner is clogged.
c. Check if the injection timing is just too early. Turn the engine and insert the engine camshaft timing pin, that is, when it's located at the upper dead center of cylinder compression, check whether the fuel pump camshaft lock pin is often inserted. If it can't be inserted, the fuel injection system timing is wrong and wishes to be adjusted.
d. Check whether the fuel pump supply is just too large.
e. Check if the fuel injection system pressure and spray condition of the fuel injector is good, and therefore the fuel injector shouldn't have a dripping phenomenon.
f. The working condition of every cylinder shall be checked by the oil-breaking method.
g. If the above inspection is normal, but the fault remains, check whether the cylinder pressure and piston, seal, and cylinder clearance are abnormal, whether the cylinder gasket is broken or the valve isn't tightly closed, etc.

3. Diagnosis and treatment of engine thermal starting difficulties

The cold start of the engine is sweet, but after running for a period of, temperature rises and therefore the engine turns off. it's difficult to start out again.


It is mainly caused by the serious wear of plunger pair of fuel injection system pump and needle valve pair of the fuel injector. When the recent car starts, the fuel viscosity is reduced thanks to the heat of the fuel injection system pump and filterand therefore the starting speed is low, and most of the diesel fuel leaks from the worn gap, leading to insufficient starting oil and unable to start out.

Diagnosis and treatment
a. the tactic of emergency elimination is: the car is hung up and driven by other cars. Using the speed of the car to drive the high-speed rotation of the engine, in order that the diesel can't leak, to make sure the starting fuel supply (this method isn't recommended, because the cylinder pressure of Cummins supercharged engine is comparatively large, the impact force on the connecting parts when the trailer starts is large, affecting the vehicle service life).
b. When the plunger pair or needle valve pair is seriously worn, the new product should get replaced after the inspection and debugging of the fuel injection system pump test bench.

4. Diagnosis and treatment of engine with normal low speed and short time high speed with insufficient smoke exhaust

The engine idle speed is sweetand therefore the throttle speed is often increased rapidly. However, the continual boom throttle speed isn't easy to rise, the driving is weak, or the medium speed isn't ready to drive. this is often caused by insufficient low oil supply.


a. filter or the oil-water separator is blocked.
b. low oil circuit isn't smooth.
c. Insufficient oil supply in the pump or the filter is blocked.
d. The inlet valve of the fuel tank cover is invalid.
All of the above conditions can cause the fuel pressure of the low oil chamber of the fuel injection system pump to be insufficient, and only the oil supply amount required for the tiny load is often maintained. when it's necessary to use more oil supply for giant and medium load, it can't be satisfied, leading to a weak driving.

Diagnosis and treatment
a. Check whether the valve of the tank cover is invalid, if it fails, a particular vacuum degree is going to be formed within the tank, and therefore the diesel fuel can't be sucked out. Most of this phenomenon is caused by the loss of fuel tank cover and sealing with airtight plastic cloth.
b. Check if there's any concavity within the low oil pipe and whether there's any blockage at the inlet pipe joint filter.
c. If the filter or oil-water separator isn't replaced for an extended time, it should get replaced in time.
d. Check if the pump is functioning properly. If the oil supply is insufficient, replace or repair the pump in time.

5. Diagnosis and repair of low engine speed but no high speed, insufficient smoke exhaust

The low speed of the engine is sweet, but the speed can't be increased at the time of acceleration, and therefore the driving is weak, which is caused by insufficient circulating oil supply.


a. The fuel injection system pump isn't adjusted properly, in order that the fuel supply is reduced.
b. The governor spring is reduced in elasticity thanks to fatigue. When the throttle is stepped to the top, the oil adjustment lever can't move forward to the topin order that the fuel supply of the fuel injection system pump is reduced and therefore the engine cannot reach the rated speed.
c. The fuel pump plunger and therefore the sleeve, the injector needle valve, and therefore the needle valve body are seriously worn, in order that the diesel fuel leakage increases when the oil is pumped, and therefore the oil supply amount is comparatively reduced.
d. Improper adjustment of the throttle control lever or the accelerator pin is just too far, the accelerator can't be placed in situleading to insufficient oil supply at full load.
e. there's air within the oil circuit

Diagnosis and treatment
When the engine power is insufficient, if the low speed is sweet and therefore the smoke exhaust is normal, it means the engine burns well, that is, the diesel injection quality is sweet, the fuel supply start time is normal, the cylinder sealing is sweet and therefore the intake air is sufficient.
a. within the case of a normal low-pressure oil circuit, first check whether the degree of looseness of the accelerator connecting pin and therefore the length adjustment of the rod is properly adjusted. When the throttle is stepped to the top and therefore the governor's arm is at the utmost position, the high regulation screw should be in touch with the limit block. Otherwise, it should be adjusted.
b. Drain the air from the oil circuit.
c. Debug the fuel injection system pump on the test bench to eliminate the fault.


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