FUEL SYSTEM
Fuel Injection Pump / Governor / Timer
6-24 6LY3 Service Manual
© 2007 Yanmar Marine International
Troubleshooting the Fuel Injection
System
Complete repair means not only replacing defective
parts, but also finding and eliminating the cause of
the trouble. The cause of the trouble may not
necessarily be in the pump itself, but may be in the
engine or the fuel system. If the pump is removed
prematurely, the true cause of the trouble may
never be known. Before removing the pump from
the engine, go through the basic inspection items
listed here.
Basic Checkpoints
• Check for breaks or oil leaks throughout the fuel
system, from the fuel tank to the nozzle.
• Check the nozzle spray pattern.
• Check the fuel delivery system operation. Loosen
the fuel pipe connection at the injection pump
inlet and test the fuel feed pump.
Major Faults and Troubleshooting
Fault Cause Remedy
Engine won’t start. Fuel not delivered
to injection pump.
1. No fuel in the fuel tank.
2. Fuel tank cock is closed.
3. Fuel pipe system is clogged.
4. Fuel filter element is clogged.
5. Air is drawn into the fuel due to defective
connection in the piping from the fuel tank to
the fuel pump.
6. Defective valve contact of the feed pump.
7. Piston spring of the feed pump is broken.
8. Inter-spindle or tappets of the feed pump are
stuck.
1. Fill Tank.
2. Open.
3. Clean and clear.
4. Disassemble and clean,
or replace element.
5. Repair.
6. Repair or replace.
7. Replace.
8. Repair or replace.
No fuel delivered
to injection pump.
1. Plunger is worn out or stuck.
2. Delivery valve is stuck.
3. Control rack will not move.
1. Repair or replace.
2. Repair or replace.
3. Repair or replace.
Nozzle doesn’t
work.
1. Nozzle valve doesn’t open or close normally.
2. Nozzle seat is defective.
3. Injection nozzle starting pressure is too low.
4. Nozzle spring is broken.
5. Fuel filter is clogged.
6. Excessive oil leaks from the nozzle sliding area.
1. Repair or replace.
2. Repair or replace.
3. Adjust.
4. Replace.
5. Repair or replace.
6. Replace the nozzle
assembly.
Injection timing is
defective.
1. Camshaft is excessively worn.
2. Roller guide was incorrectly adjusted or is
excessively worn.
3. Plunger is excessively worn.
1. Replace camshaft.
2. Adjust or replace.
3. Replace plunger assembly.
Engine starts but immediately stops. 1. Fuel pipe is clogged.
2. Fuel filter is clogged.
3. Air is entering fuel lines.
4. Insufficient fuel delivery from the feed pump.
1. Clean.
2. Disassemble and clean, or
replace the element.
3. Replace the packing repair
pipe.
4. Repair or replace.
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