Yanmar 6LY3 series Service Manual page 305

Troubleshooting by Symptom
12/05
Trouble symptom
Engine speed is not stable.
Malfunction of the fuel
injection nozzle.
Uneven fuel injection
volume.
6LY3 Service Manual
Causes
If low idle hunting occurs, follow these individual steps and check the effect after each step.
1) Change the control gain pattern with a YDT.
2) Raise the low idle speed with 20 rpm step.
3) Check the following items. If a malfunction is found, repair or replace.
4) Replace the fuel injection pump.
NOTICE: In case of trolling issues, check the faulty trolling end or reduction gear end.
When the rotational fluctuation is not cyclic, the wire harness may be broken. The harness
can be checked by operating the engine with the harness for the test. (DTC can be
detected by coming off the output range of the harness.) The signal output line is
short-circuited with other lines fixed to a 3V. 5V line or the grounded line is short-circuited
with a 3V line and the output drops.
Faulty valve and / or seat.
Sticking needle valve.
Wear of seat.
Clogged fuel injection
hole(s).
A decrease in fuel opening
pressure.
Faulty movement of the fuel
injection pump plunger.
Damaged fuel injection pump
plunger.
Damaged plunger spring.
Improper installation of the
fuel injection pump.
Clogged fuel filter.
Clogged fuel system.
Air in the fuel system.
Faulty movement of the fuel
feed pump.
Faulty actuation of the
hydraulic timer.
Engine is overloaded.
Seized main moving part(s).
Clutch slip.
© 2007 Yanmar Marine International
TROUBLESHOOTING
Corrective action
Check the fuel spray
condition with a tester. If a
malfunction is found, send it
to the FIE shop for service or
replacement.
Check. If a malfunction is
found, send it to the FIE shop
for service or replacement.
(If measuring lag with a YDT,
the movement of the rack
can be checked.)
Reinstall according to the
Specifications on page 6-5.
Check and replace if
necessary.
Check and repair.
Check and bleed air.
Check and repair or replace
if necessary.
Check with a YDT.
DTC: See Troubleshooting
by DTC Fault Codes on
page 13-28.
Check around the propeller
and boat hull.
Check and repair or replace
if necessary.
Check and repair or replace
if necessary.
Remarks
See Fuel Injection Nozzle
Components and Functions
on page 6-26.
Refer to the YDT Manual.
See Specifications on
page 6-5.
See Fuel Filter Components
and Functions on page 6-33.
See Fuel Filter Components
and Functions on page 6-33.
See Fuel System on
page 6-1.
See Inspecting the Fuel
Feed Pump on page 6-30.
DTC: See Troubleshooting
by DTC Fault Codes on
page 13-28.
—
See Engine on page 5-1.
Refer to the Marine Gear
Manual of another volume.
13-15