Sun Microsystems MCS 2000 SL - Page 67

t
EXHAUST
GASES
Hydrocarbons
Hydrocarbons
are
unburnt
or
partly
burnt fuel.
High
levels
of
hydrocarbons
(Measured
in Parts
Per
Million
-
PPM) in
the
exhaust
gas
are
often related
to
problems
in
the ignition
system, fouled
p1ugs, poor
ignition
wires, improper
timing
or
dwell,
vacuum
leaks
olincorrect
,'Air/Fuel"
ratios,
all cause
improper
combustion
and
high
HC readings.
Carbon
Monoxide
CO
is
formed
when
there is not
enough oxygen
present
during
combustion.
High
levels
of carbon
monoxjde
(Measured
as a
percentage
%
volume
of
the
exhaust
gas)
can
be
caused by a too
rich
mixture,
low
idle
speed,
incorrect
float
1evel,
blocked air
filter,
malfunction
of
the PCV valve
or
incorrectly
adjusted
carburettor
or
injection
system. Low
oxygen
available.
This
could
be cailed
oxygen
starvat'ion. The
solution
is to
reduce the
amount
of
fuel.
Carbon Dioxide
CO2
(Measured
as
a
percentage
% volurne
of the
exhaust
gas)
is
an
important
diagnostic
clue
to
the
efficiency
of
the
combustion
process.
Carbon Monoxide
(One
part
Carbon to
one
part
Oxygen) is the resu'lt
of too
little
oxygen
in
the
combustion
process.
Carbon
Dioxide
(One
part
Carbon
to two
parts
oxygen)
is the result
of
a
more
efficient
combustion. The
greater
the
percentage
of
COZ
in
the
exhaust
gas,
the more
efficient
the
engine is running.
A reading
of
'13%
to 15%
is
considered'ideal,
with
CO
and HC
at or near
to
zero
and oxygen
within
'l%
to
3%.
Oxygen
02
(Measured
as
a
percentage
% volume)
jndicates
the
accuracy
of the
carburettor
sett'ing.
If the
oxygen
content is
measured
as
the
Air/Fuel
ratio
is
adjusted from
rich
to 1ean,
or lean
to rich,
a
step
jump
jn
the reading
of
at
least
0,5
% shows
the
crossover
point
from rich
to lean.
02 measurement
is
also
useful in
detecting
vacuum
leaks
and ignition
problems
causing
a
misfire
and
of course
an
incorrect
sample
because
the
exhaust
probe
is
not
correctly
inserted
and/or the
exhaust
system is
leaking.
Oxygen
readings
of
1,5
% or less
is
considered
ideal
with
HC
and
CO
at or
near
zero
and
CO2 with'in
the range
of 13
% to 15
%.
Page
61
L
L