Typical generator fault finding procedure


Listed below are typical faults which may occur together with the action required to remedy the fault.




Fault                                        Possible cause

Engine will not turn
a) Battery discharged. Loose or incorrect cable connections. Electrical

fault in starting circuit.

b) Faulty starter motor.

c) Starter pinion will not engage on flywheel starter ring.


  1. Check
    • Voltage at battery terminals. If no voltage change or put on
    • Voltage at starter motor
  2. If voltage present:
    • Check all
    • Change starter
  3. Turn engine by the tools provided and repeat attempt to start. Replace starter motor if fault remains.


Fault                                        Possible cause

Engine will not fire
a)   No fuel reaching injectors. Fuel supply line blocked.

b)   Air lock in fuel line.

c)   Fuel filters choked.

d)   Water in fuel.

e)   Air cleaners choked.

f)    Fuel pump timing out.

g)   Lift pump faulty.


  1. Operate excess fuel
  2. Check that fuel tap is ‘on’ and adequate amount/head of fuel is in
  3. Bleed fuel system.
  4. Change filter elements on engine. Drain contaminated fuel. Empty fuel filter bowls and change elements.
  5. Clean air
  6. Reset
  7. Change lift


Fault                                        Possible cause


Engine fires but fails to pick up speed




  1. Fuel supply system
  2. Air cleaner
  3. Faulty lift
  4. Faulty air


  1. Check all pipe joints. Bleed fuel
  2. Clean air
  3. Change lift
  4. Change injector(s).


Fault                                        Possible cause

Engine misfires
a)   Air lock in fuel line.

b)   Fractured injector feed pipe. Faulty injector.

c)   Faulty injection pump.

d)   Tappet clearances incorrect.


  1. Bleed fuel system. Replace
  2. Loosen feed pipe to each injector in turn and note any change in engine
  3. Change injection
  4. Check and readjust tappet clearance


Fault                                        Possible cause

Low power output
a)   Inadequate fuel pressure.

b)   Air filters choked.

c)   Fuel injection pump timing incorrect.

d)   Faulty injection.

e)   Tappet clearance inadequate.

f)    Faulty turbocharger.

g)   Inlet manifold and/or cylinder head joints leaking


  1. Check over complete fuel supply system as previously laid
  2. Clean air
  3. Reset
  4. Change injector(s).
  5. Adjust
  6. Replace
  7. Renew gasket or joint packings as



Fault                                        Possible cause


Low oil pressure (Sudden pressure drop as opposed to progressive drop due to worn bearings)


  1. Oil level too low.
  2. Oil pressure gauge
  3. Oil filters
  4. Relief valve



  1. Check for leaks and fill to level indicated on
  2. Fit an identical replacement
  3. Change filter elements.
  4. Examine and clean pressure relief


Fault                                        Possible cause

a)   High oil temperature.

b)   No coolant in engine.

c)   Coolant system polluted.

d)   Blocked air passages in radiator matrix.

e)   Fan belt tension incorrect.

f)    Thermostat fault.

g)   Fuel injection pump timing out.

h)   Low oil level.


  1. Check out as detailed in ‘overheating’
  2. Check for leaks and refill (ensure correct percentage of anti-freeze is also added if necessary).
  3. Drain, flush out and
  4. Carefully clean all air
  5. Adjust tension.
  6. Fit an identical replacement
  7. Reset
  8. Check for leaks &fill to level indicated on


Fault                                        Possible cause

Inadequate fuel
a)   Fuel supply system faulty.

b)   Faulty fuel lift pump.

c)   Fuel relief valve faulty.

d)   Choked fuel filters.


  1. Check all pipe joints for
  2. Replace with identical
  3. Examine and clean
  4. Change filter elements.



Fault                                        Possible cause

Exhaust emits black smoke     Excess fuel being used.


Change pump if maximum fuel stop seal has been broken.


Fault                                        Possible cause

Machine    becomes    over-   a) Cooling air inlet blocked or obstructed. heated                                      b) Cooling air discharge blocked or obstructed.

c)   Rotor bearings running hot.

d)  Machine overloaded.

e)   Short circuit between windings and/or windings to frame.


  1. Clean screen protection and remove any obstruction preventing air entering the air
  2. Proceed as for air inlet above.
  3. Too much or too little grease. Remove bearing from machine and check conditions. Repack with correct grade and quantity of grease before
  4. Check that the electrical overload equipment and circuit breaker are working
  5. Replace



The faults liable to occur in this equipment will depend upon the design of the control scheme supplied. It is only possible to give general recommendations regarding fault findings on this equipment.


Fault                                        Possible cause

Circuit fuses blowing
a)   Incorrect rating of fuse used.

b)   Short circuit between panel wires and/or between wires and frame.


  1. Check circuit rating and fit new fuse of the recommended
  2. From circuit diagram check wiring of components. Rewire or replace components found


Fault                                        Possible cause

Circuit  operating  satisfac-   Faulty or out of adjustment relay or auxiliary contacts. torily only intermittently


Replace and/or readjust auxiliary and clean where necessary.



Fault                                        Possible cause

Excessive   50   Hz buzz or     Dirty, rusty or badly aligned pole faces hum


Clean, de-rust with fine emery paper and readjust.

Leave a minute film of oil on the parts concerned to retard formation of rust.


Fault                                        Possible cause

Overheating cable ends and    Loose connections. terminations


Tighten all connections, making sure all dangerous voltages have first been switched off and cannot be switched on again whilst work is in progress.

Ensure all terminations subject to heat/load cycling i.e. the main cabling terminations are suitably lock nutted.



In all instances it is recommended that for specific fault finding instructions the manufacturers handbook be referred to as designs vary in detail from manufacturer to manufacturer. The details given below are for general guidance only.


Fault                                        Possible cause

No output voltage
a)   Engine speed too low.

b)   Loose terminals.

c)   No excitation and/or loss of residual magnetism.

d)   Open circuit in windings.

e)   Faulty automatic voltage regulator (AVR).

f)    Faulty diode in main rectifier assembly on the rotor.

g)   Open circuit of the gain and/or range control on the AVR.

h)   Hand operated voltage trimmer open circuit (if fitted).


  1. Check and set up
  2. Check over and tighten all
  3. Re-excite by flashing in accordance with manufacturers
  4. Check for continuity in accordance with manufacturers handbook: renew if
  5. Remove leads at voltage control unit terminal block, run set up to speed and flash excitor in accordance with the manufacturer’s handbook. If the voltage appears then the AVR is faulty and should be tested out in accordance with the instructions given for testing V.R.’s.



  1. Remove and test with ohmmeter; the forward resistance should be less than 1000 ohms and the reverse resistance greater than 100K ohms. Replace if necessary. N.B. When this fault occurs it is likely that more than one and possibly all the diodes may need
  2. Check for


Fault                                        Possible cause

Output voltage unstable
Incorrect setting of gain control.


Adjust slowly until a stable voltage is obtained.


Fault                                        Possible cause

Output voltage incorrect
Voltage set up incorrectly on band trimmer or choke tappings.


Adjust accordingly.


Fault                                        Possible cause


Output voltage too high and cannot be reduced on controls


Automatic voltage regulator faulty.


Remove AVR and make recommended tests. Replace if found necessary.

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