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Instructions For Engine Low Output and Abnormal Troubles

Dec. 28, 2017

This is the part two of Shangchai SC27G diesel engine troubleshooting guidelines. In the first part, we have already learned the details of engine will not start. In this part, we are going to learn the features and possible cause of engine power output low and abnormal noise and vibration. Following each feature and possible cause, the related correction is provided for solving problems.

Instructions for Engine Abnormal Noise, Vibration

(2) Engine Power Output Low



Fault Feature



Possible Cause




Power or speed does not go up after increasing the fuel supply.



Failure of fuel system:


(1) The fuel pipeline broken, or leakage at the pipeline joints, fuel filter blocked or air in the fuel system.


(2) Not enough fuel, or water and impurity in the fuel tank.


(3) Incorrect fuel supply pump timing.


(4) Not enough fuel supply from the fuel injection pump.


(5) Poor fuel atomization or low injection pressure.




Replace the damaged fuel pipe, tighten the joints, clean the strainer, replace fuel filter, and priming the fuel system.


Make sure there is enough fuel in the fuel tank. Discharge water and sediments in the fuel tank. Change the fuel in the tank with clean fuel if necessary.


Check and adjust the fuel injection pump timing.


Check the fuel injection pump and replace it if necessary.


Let a professional serviceman inspect the injector for injection spray and injection pressure, and make adjustment. Replace the injector(s) if necessary.



Higher exhaust temperature and poor smoke at normal working condition.



Failure of inlet and exhaust system:


(1) Block of the air filter.


(2) Leakage in the intake system.


(3) Block of the exhaust pipe, the connecting pipe too long, or with too small elbow, or with too many elbows.


(4) Wrong fuel injection pump timing.



Clean the filter element and replace it when required.


Check the pipeline somewhere between the outlet of the compressor and the inlet of intake manifold for leakage and remove the leak source.


Remove the carbon deposit inside the exhaust pipe, reduce elbows to no more than 3 and increase across area.


Check and adjust the valve clearance and refer to Section of 5.3 for the procedure.


Check and adjust the fuel injection pump timing.



Poor engine performance at all speeds.



Change of fuel injection pump timing.



Check and adjust the fuel injection pump timing.



Engine overheat.



(1) Ambient temperature too high


(2) The temperature of lube oil and cooling water are very high and the exhaust temperature is also high.



Improve the ventilation condition and take a good temporary cooling measure if the ambient temperature is too high.


Check and repair the cooler and radiator, and remove the scale. Inspect the diameter of relevant pipelines for too small across areas.



Not only low power output and poor engine performance, but also gas leak, black smoke from the intake pipe and knocking noise.




Failure of cylinder head group:


(1) Looseness of the cylinder head nuts or the damage of the cylinder gasket due to gas leak from the joint plane of cylinder head and engine block, especially flowing out from the cylinder head gasket during transit operation.


(2) Leakage at intake or exhaust valve(s)


(3) Valve spring(s) damaged.


(4) Wrong valve clearance.


(5) Leakage at fuel injector hole or the damage of injector copper washer.


(6) Insufficient compression pressure due to the seizure of piston ring or valve stem.



Tighten the cylinder head nuts to the defined torque. Replace the cylinder head gasket, and repair the joint plane if necessary.


Disassemble and inspect the intake and exhaust valve, repair and grind. Replace the valve seat(s) or and valve(s) if required.


Replace and adjust the valve clearance and refer to Section of 5.3 for the procedure.


Check and repair the damaged parts.


Replace the relevant parts when required.


Check the piston rings, piston, cylinder lines and valves. Make replacement if necessary.



Abnormal noise and drop of the oil pressure.




Seizure of the connecting rod bearing(s) and crankshaft.



Check the large end of connecting rods for the side clearances as well as backward and forward movement. If the connecting rods cannot movement, repair the crankshaft pin and change the connecting rod bearing(s).



Drop of speed, decrease of inlet air pressure, air leak or abnormal noise, etc.




Fault of the turbocharger:


(1) Wear of the turbocharger bearing and contact of the blades of the compressor or turbine to their housings.


(2) Dirt and block of the compressor and air leak at inlet pipe(s).



Let a professional serviceman check the turbocharger. Make replacement if necessary.


Let a professional serviceman clean the compressor housing and impeller. And tighten the joint nuts and clamps.



(3) Abnormal Noise And Vibration



Fault feature



Possible cause




There is rhythmic and clear metal slapping noise made by in the cylinder.




Too early fuel supply.


Check and adjust the fuel injection pump timing.


There is low and non-clear slapping noise in the cylinder.




Too late fuel supply.


Check and adjust the fuel injection pump timing.



There is light and speculate noise, which is clearer during idle running.




Clearance between piston pin and small end bushing of connecting rod is too big.


Check the small end bushing of he connecting rods and replace the connecting rod(s) if necessary.


There is collision noise in crankshaft case during running. There is heavy and forceful collision noise when reducing the speed suddenly.



Too large clearance between a crankshaft pin and connecting rod bearings due to bearing wear.



Check the piston and liners for ware and make replacement of piston or liner according to wear condition.



If you are dealing with any problem mentioned above, please find associated corrections. This is the part two of Shangchai SC27G diesel engine troubleshooting guidelines, there are more information will be updated in other posts.


For the information about Shangchai G series diesel engine operation and maintenance, please visit:

Shangchai G Series Diesel Engine Operation And Maintenance Manual

Shangchai G Series Engine Nameplate And Specifications

SC27G Diesel Engine installation and Connection

SC27G Diesel Engine Operation And Engine Start

SC27G Diesel Engine Maintenance Instructions

SC27G Diesel Engine Maintenance

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