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Troubleshooting for Diesel Engine Temperature, Injection and Governor

Dec. 05, 2017

This is the part II of Yuchai YC4108D/YC4108ZD diesel engine troubles and troubleshooting. It contains the examples of normal troubles that users will encounter during operating diesel engine and many remedies are provided to different troubles. The problems include high oil pressure, much diluted oil, excessive oil consumption, high water outlet temperature, engines stop automatically, engine over-speeding and other troubles like injection and governor. 

yuchai diesel engine

I. Too High Oil Pressure, Much Diluted Oil, Excessive Oil Consumption


Possible causes



1. Too high diesel engine load


Be careful not to pull out the lead seal on

the injection to avoid engine operating

forepartwhich will damage the engine



2. Incorrect engine oil grade


Select oil according to the brand prescription.


3. Piston ring stuck or seriously worn causing gas blow - by and oil pumping - up.


Dismantle, check and clean the piston an  piston ring, replace the piston ring and cylinder sleeve if necessary.


4. Oil groove and bore of piston and piston ring clog.


Dismantle and clean, and then reinstall it.


5. Oil cooling plug clog


Clean,replace if necessary.


6. Diluted oil due to diesel or water in it


Check the cylinder sleeve seal ring, oil cooler, injection pump, injector, cylinder head, and cylinder head washer, replace them if necessary.


II. Too High Water Outlet Temperature



Possible causes




1. Insufficient cooling water or too small water flow


Check the level of cooling water, add water to adequacy if necessary; check for looseness of the belt, adjust it if necessary; check for leakage of the water pump, repair it in time if necessary; check and replace the damaged thermostat.


2. Too much scale in water passage and tank


Clear it


3. Thermostat failure


Check and replace the damaged thermostat


4. Water temperature indicator damaged and transmitter failure.


Check and compare the actual temperature with the indication, if they are not same, replace the transmitter or water temperature indicator.


5. Cooling fan damage


Repair or replace


6. Water pump damage


Repair or replace.


III. Engine Stops By Itself



Possible causes




1. Fuel is used up


Check and add fuel, and remove the air in the oil line


2. Oil line clogged or much air entering


Check and clear the oil line; remove the air in the oil line; determine the location of the intake and then remove it.


3. Bushing burned due to the blockage in lubrication oil line.


When the water temperature is normal, will lead to engine to stop immediately.

Dismantle the sump, check and repair it and then replace the damaged parts.


4. Overheat piston scraping due to lack of water or too high water temperature.


At first,make engine cool naturally(make sure not to add cold water or wash engine with it),then try to rotate the crankshaft. If it is jammed, start engine after adding cold water, or else move engine, check and repair it, then replace the damaged parts.


IV. Engine over-Speed (Speed Rises Sharply)


Possible cause




1. Injection pump  ( governor) is in trouble


Pull the stop handle when engine over speeding, if the engine is fail to stop, brake it with engaging a gear in transmission,or other measures should be taken to force it to stop, such as sealing off the in let, cutting off the fuel pipe and etc. After engine has stopped, adjust and repair it, replace the damaged parts if necessary.


V. Common Trouble And Troubleshooting Remedies For Injection



Possible causes




1. Injection failure:

A. No oil in oil tank.

B. Air or leaks in oil line.

C. Oil line clogged.

D. Fuel pumps failure.

E. Plunger precision pair worn out, snapped or spring cracked.



Check and add oil to adequacy.

check and remove air, block up the leakage.

Check and remove the blockage.

Determine the location of the trouble and repair it. 

Determine the location of the damaged part and repair it.


2. Insufficient or uneven outlet 

A. Insufficient inlet oil pressure.

B. Leaky oil outlet valve or spring crack.

C. Plunger precision pair is out of order due to dirty or much wear.

D. Loose plunger control gear.


Check the condition of fuel pump and blockage of oil line, if necessary, remove it.

If there is leakage, lap in pair; if there is damage, replace parts.

Check and wash the oil line and precision pair, and replace the much worn one.

Check for the looseness of the plunger control gear, tighten to the signal if necessary; regulate the injection pump on test bench better.



VI. Common Trouble And Troubleshooting Remedies For Governor


Possible causes



1. Unsteady speed  (engine hunting)

A. Inflexible flyweight or fly weight holder of governor.

B. Improper idle adjustment

C. Governor components worn out



Determine the location of the troubles, and then repair it,replace parts and wash it if necessary.

Readjust the idle adjusting screw.

Check and repair it(By specialist manufactures)


2. Speed always lower than calibrated speed.

A. Adjusting spring deflection.

B. Control handles mis - positioning.

C. Adjusting rack and pull bar jammed or loose.


Regulate properly and replace the spring by professionals, do not do it without authorization.

Determine the location the blockage, and then regulate and remove it.

Check and adjust it, then ensure the rack slides flexibly arid the gear ring is not loose, otherwise readjust and repair it.



3. Speed rising promptly to abnormal state( runaway).

A. Adjusting rack or throttle pull bar stuck.

B. The pin connecting adjusting rack and pull bar drops.

C. Governor spring crack.


Regulate and repair it

Reinstall it and, if necessary,  replace the damaged parts.

Replace it and then readjust the injection pump on test bench.


VII. Common Trouble For Fuel Supply Pump



Possible causes




1. Check valve and piston wear or spring crack


Check and repair, replace it if necessary.


2. Oil leak around joints


Tighten or replace the seal gasket.


3. Outlet screen clog


Check and clean it.


4. Oil and air leak around hand pump


Dismantle and repair, replace it if necessary.


VIII. Common Trouble And Troubleshooting Remedies For Injector


Possible causes




1. Bad atomization of injector and insufficient or without fuel injection.

A. Needle precision pair stuck and injection orifice clogged.

B. High pressure pipe joints leakage

C. Dirt on surface of needle



Clear the carbon deposit and dirt. Clean and grind it,replace if it cannot be recondition.

Determine the location of the troubles, and then recondition or replace it.

Clean it.


2. Low injection pressure

A. Pressure  adjusting screw looseness

B. Pressure adjusting spring crack

C. Pressure adjusting spring deflection

D. Spring seat and stem damage

E. Needle stuck



Readjust and tighten the stud.

Check and replace.

Check and replace.

Repair or replace the damaged parts.

Clean and grind it


3. Injector oil leak:

A. Bad seal of needle precision pair.

B. Needle stuck

C. Nozzle retaining nut damage and deflection

D. Sealing surface of injector body and needle body damage.


Grind it after cleaning, replace it if ineffective.

Clean and grind, replace it if ineffective.

Replace it.

Lap in pair after cleaning, replace it if it can not be reconditioned.


For more normal troubles and troubleshooting information:

Yuchai Diesel Engine Normal Trouble And Troubleshooting

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