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Yuchai Diesel Engine Normal Trouble And Troubleshooting (1)

Dec. 02, 2017

Determine the location of the troubles and remove them immediately when diesel engine does not operate normally. Forbid running a malfunctioning vehicle, or it will affect the work of Yuchai engines.

 Engine Troubleshooting


The manual presents common troubles and troubleshoots methods only for reference. Because the knowledge about troubleshooting is simple and not comprehensive, please pay more attention to it. When not being sure of the trouble cause, do not tackle it without authorization to avoid larger damage. It should be done that informing and consulting with technical Yuchai service station or asking the near special units to deal with.

I. Diesel engine can not start or start difficultly


Possible causes



1. Insufficient power or bad terminals connection contact



Charge or replace the battery. Check for looseness of the contacts of the electrical equipment or bad contact due to rustiness 'and then deal with it.

2. Fuel pipe clogged or insufficient oil supply



Determine the location of the clog and clear it. Clean filter element.

3. Air exists in the oil line


Check for looseness and damage of the joints of fuel pipe, remove or replace them if necessary and then clear air in the oil line.

4. Too much oil deposit in cylinder


Close the throttle, rotate the crankshaft by motor, drain excess oil deposit in cylinder, and especially par more attention to overhauled engine.

5. Fuel supply pump does not apply fuel or applies fuel irregularly


Check for leakage of the delivery valve and inspect whether injector is worm - out, plunger is seized, and if plunger spring and delivery valve spring is broken. Remove them in time.

6. insufficient compression pressure due to piston ring or Cylinder much worm - out;


Check and replace the piston ring or Cylinder


7. Blow - by valve


Check the valve clearance and seal of valve.

Grind or readjust the valve if necessary.

8. Incorrect fuel injection advance angle


Check and adjust it

9. Incorrect valve timing


For the overhauled engine, pay attention to the Timing marks alignment on timing gears.


II. Insufficient power output


Possible causes


1. Oil advance angle changes


Check and adjust according to regulation

2. Faulty injector


Check the working pressure or atomization of the injector, replace the needle valve precision pair if necessary.

3. Incorrect intake and exhaust valve clearance or bad seal of valve


Check and adjust the valve clearance ac of the injector, replace the needle valve the valve, grind it if necessary.

4. Overheat engine


Check the level of cooling water, add enough water if necessary; check for the leakage of the water pump or the looseness of the belt, remove or require it if necessary; check for thickness of scale in water passage, remove it if necessary.

5. Air cleaner choking


Replace the filter element.

6. Fuel supply pipe clogged


Check and clean it

7. Faulty injection pump


Check for leakage of the delivery valve and inspect whether plunger is worn- out, and if the plunger spring and delivery valve spring is broken, replace the damaged parts, cylinder gasket and readjust oil pump if necessary.

8. Cylinder gasket damage or leakage


Replace it.

9. Too high exhaust back pressure


Clear the exhaust passage and muffler

10. Excessive blow - by


Check the piston, piston ring and cylinder sleeve. If they are much worn out or ring elasticity is insufficient, replace them.

11. Intake pipe leakage( Turbo charger)


Check the oil pipe and remove leakage

12. Turbocharger is out of order


Determine the location of the troubles and remove lt


III. Abnormal noise during engine operation


Possible causes


1. Incorrect injection timing or injector stuck and high frequency knock noise in cylinder


Check the injector; replace the needle valve precision pair if necessary.check the fuel injection advance angles,if it changes, adjust to the prescription.

2. Clash due to too large clearance between piston and cylinder sleeve


Check the wear of the piston and cylinder sleeve, replace them if necessary.

3. Clash due to too large clearance between connecting rod hearing hushing, main bearing bushing and journal


Check if the bearing bushing and crank-shaft are much worn out, replace or press in the oversized bearing bushing if necessary.

4. Knock due to valve touching


Check and adjust the valve clearance. Inspect the valve timing for the overhauled

5. Clash due to too large crank shaft axial clearance


Check the wear of the thrust plate,replace it if necessary.

6. Abnormal knock due to valve spring crack


Stop immediately to check and replace the damaged parts.


7. Too large valve clearance and heavy noise around cylinder head


Adjust the valve clearance



 IV. Exhaust with abnormal smoke color


Possible causes



1. Exhaust with black smoke

deal with by the conditions of Insufficient



2. Exhaust with white smoke

A. Bad atomization of injector

B. Water in cylinder or diesel

C. Some cylinder doesn't work when operating at low speed on cold day

D. Incorrect fuel injection advance angle


Check the working conditions; replace the excessive blow -by if necessary. Check diesel, if there is water in it,replace it, Otherwise, check for damage of the cylinder head parts which may cause water leak, replace the damaged ones. Close the shutter door when the ambient temperature is low, and make the operating temperature rise quickly to avoid running long time at low temperature. Check and adjust fuel injection advance angle.

3. Exhaust with blue smoke

A. Too much oil in sump

B. Operation at zero load and low speed for too long time

C. Sticking, much wear or in verse installing orientation of piston rings, oil blow - by and bum in cylinder.

D. Oil seeps through the gap between valve guide and stem due to valve guide is much worn.


Check the level of oil, drain it if necessary.

Decrease time of the operation at zero load and low speed to avoid oil blow -by and bum in cylinder.

Replace the piston ring if necessary.

Check the clearance between the valve and guide, Replace it if necessary.


V. Too low oil pressure

Possible causes



1. Insufficient oil in sump


Add oil to adequacy.

2. Oil pipe clog or leakage


Check the detailed cause, and then clean the coarse filter element or the oil strainer

3. Pressure adjustment valve failure


Check the pressure adjustment valve, replace it if necessary.

4. Pressure indicator: or transmitter failure.


Check the cause and then replace it.

5. Diluted oil


Check if incorrect brand oil is used or oil temperature is too high.If the cause is the former, replace oil.otherwise find out the reason of the latter and then deal with it.

6. Too large assembly clearance of oil pump


Check it, replace if necessary.

7. Journal bearing wear or too large clearance


Check and replace the journal or associated parts

8. Oil cooling plug clogged


Clean it, replace if necessary.


This is only the part 1 for Yuchai diesel engine troubles and troubleshooting. If you want more infomration, please read:

Important Maintenance Tips

Diesel Engine Operation

Operation and Maintenance Tips


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