Mitsubishi S12U, Operation & Maintenance Manual

Page: 101 / 106

Chapter 9
TROUBLESHOOTING
9-7
Engine Knocks
Table 9-5 Engine knocks
Problem Cause Remedy
A
Engine knocks slightly and emits
black exhaust smoke. Fuel injection timing too retarded Refer to C-(1) in Table 9-2 .
B
Knocking is severe, and exhaust
smoke is white.
Fuel injection timing is too
advanced
Refer to C-(1) in Table 9-2 .
C
Knocking is severe in certain cyl-
inders.
Uneven fuel injection among cylinders
a Excessive fuel injection in some
cylinders
Refer to C-(2)-a in Table 9-2 .
b Fuel injection timing too
advanced in some cylinders
Refer to C-(2)-b in Table 9-2 .
D
Ignition retardation occurs and
results in simultaneous ignition to
cause severe knocking.
Improper spray of fuel by fuel injection nozzles
Fuel is not sprayed in proper con-
dition in some cylinders.
Refer to C-(2) in Table 9-2 .
E
Ignition retardation occurs fre-
quently and results in simulta-
neous ignition to cause severe
knocking.
Low engine compression
Amount of intake air is low in
some cylinders.
Refer to C-(3) in Table 9-2 .
F
Injection of fuel generates knock-
ing, and engine emits large
amount of black or gray exhaust
smoke.
When oil does not rise, engine
does not knock severely and
emits bluish white exhaust
smoke.
Engine oil rising above pistons
a Oil level too high in crankcase
Discharge oil to appropriate level.
b Worn piston rings or sticking of
piston rings, resulting in inade-
quate scraping of oil
Check crankcase breather pipe
for gas leak, and replace if there
are defective parts.
c Excessive clearance between
cylinder and piston
Check crankcase breather pipe
for gas leak, and replace if neces-
sary.
d Engine oil viscosity too low
Change to high-quality oil with
higher viscosity.
G
Abnormal noise produced when
injection is stopped suddenly and
engine is allowed to rotate by
inertia
(engine mechanical failure)
a Excessive connecting rod bear-
ing clearance, or bearing metal
flaking.
Disassemble and inspect, and
repair or replace if necessary.
b Loose connecting rod cap tight-
ening bolts
Disassemble and inspect, and
repair or replace if necessary.
c Excessive clearance between
cylinder and piston
Check crankcase breather pipe
for gas leak, and replace if neces-
sary.
d Piston hitting foreign item fallen
inside cylinder
Disassemble and inspect.
H
Low compression temperature
and retarded ignition cause
severe knocking, especially after
engine starts in cold weather.
Engine too cold
Operate engine until it warms up
before increasing engine speed.