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.