General Diesel Engine Diagnostic Guide                                   
 
The following is a general diesel engine diagnostic guide.  It may not be 100% effective for Jinma series of diesel engines.  
 
Symptom Cause Remedy  
Black or Dark Gray Smoke  
Smokes under load, especially at high and medium speed.  Engine is quitter than normal. Injector pump timing retarded Set timing  
Smokes under load, especially at low and medium speed.  Engine is noisier than normal. Injector pump timing advanced Set timing  
Smokes under load at all speeds, but most apparent at low and medium speeds.  Engine may be difficult to start. Weak cylinder compression Repair engine  
Smokes under load, especially at high speed. Restricted air cleaner Clean/replace air filter element  
Smokes under load, especially at high and medium speed.  Power may be down. Dirty injector nozzle(s) Clean/replace injector(s)  
Smokes under load, especially at low and medium speed.  Power may be down. Clogged/restricted fuel lines Clean/replace fuel lines  
Puffs of black smoke, sometimes with blue or white component.  Engine may knock. Sticking injectors Clean/replace injector(s)  
 
Blue, blue- gray, or gray-white smoke  
Whitish or blue smoke at high speed and light load, especially when engine is cold.  As temperature rises smoke color changes to black.  Power loss across the full RPM band, especially at full throttle. Injector pump timing retarded Set timing  
Whitish or blue smoke under light load, after engine reaches operating temperature.  Knocking may be present. Leaking injector(s) Repair/replace injector(s)  
Blue smoke on acceleration after a prolonged period at idle.  Smoke may disappear under steady throttle. Leaking valve seals. Replace seals.  Check valve guide/stems.  
Persistent blue smoke at all speeds and loads, and operating temperatures. Worn rings/cylinders. Overhaul/rebuild engine.  
Light blue or whitish smoke at high speed under light load.  Pungent odor. Over-cooling Replace thermostat  
 
Engine cranks slowly but does not start. Cranking system malfunction Check battery, cable terminators, and starter motor  
  Crankshaft bound,  viscosity Bar engine over by hand.  If it appears tight, check oil for ethylene glycol leaks into sump.  
  Faulty injectors Check injector opening pressure.  
Cranking speed erratic, engine does not start. Valves out of time Check valve timing  
Engine cranks normally, but does not start. Glow plus inoperable Check glow plugs, control circuitry  
  Incorrect or contaminated fuel Check fuel supply  
  No fuel to cylinders Trace the supply forward from tank to transfer pump, transfer pump to high pressure pump (which may be the same unit), high pressure pump to injectors, injectors to nozzles.  
  Incorrect pump timing Check timing  
  Air intake restriction Check filter element  
  Exhaust system restriction Check system  
  Low compression Test cylinder compression  
Engine does not idle Incorrect idle adjustment Correct adjustment  
  Air in fuel system Bleed system, tighten connections.  
  Clogged fuel filter(s) Replace filter(s)  
  Fuel return line restricted Disconnect line to verify restriction and remove obstruction  
  Air inlet restriction Replace filter element  
  Exhaust system restriction Repair system  
Engine runs erratically at low speed Any of the idle malfunctions above. Check as indicated  
  Loss of compression in one or more cylinders Test cylinder compression  
Engine does not develop normal power Insufficient fuel supply Check filters, transfer pump, cap vent, for possible air leaks into system.  
  Incorrect or contaminated fuel check fuel supply  
  Injection timing error Check timing  
  Air inlet restriction Check filter element  
  High pressure fuel system malfunction Check high pressure system, beginning with leaks and concluding with pump calibration  
  loss of engine compression Test cylinder compression  
Engine knocks excessively Defective injector(s) Test by substitution  
  Restricted fuel return line Open line to verify, remove obstruction  
  Injection pump malfunction Test pump  
  Bearing knock Verify and repair engine.