Mityvac 06820 Diesel Compression Test Adapters - Manual (Page 10)

Page Number - 10
Form 822378
POSITIVE CRANKCASE VENTILATION SYSTEM
SYSTEM OPERATION
The Positive Crankcase Ventilation (PCV)
system is used on all modern engines to
reduce air pollution by providing a more
complete scavenging of crankcase
vapors. Air is drawn through a filter
located in the air cleaner, through a hose
in the valve cover, into the crankcase,
across and up into the rear of the intake
manifold or opposite valve cover, through
the PCV valve, through a hose, into the
intake manifold. Intake manifold vacuum
draws in all vapors from the crankcase to
be burned in the engine.
When air flow through the carburetor or
throttle body is high, added air from the
PCV system has no effect on engine
operation.
However, at idle, air flow through the
carburetor or throttle body is so low that
any large amount added by the ventilation
system would upset the air/fuel mixture,
causing a rough idle. For this reason, the
PCV valve restricts the ventilation system
flow when intake manifold vacuum is
high.
SERVICE PROCEDURES
After a period of operation, the PCV
valve may become clogged and reduce
the amount of crankcase ventilation. The
PCV valve should be replaced periodically
to prevent the formation of acids in the
crankcase and the build up of excessive
crankcase pressure, which could force
engine oil out past the seals. Use the
following procedure to check the PCV
system using your pump:
1) Inspect the system for kinked, plugged
or deteriorated hoses. Check to be sure
all hoses are connected properly.
Repair as necessary.
2) Connect your pump to an intake
manifold port and check the vacuum
reading of the warmed and idling
engine.
3) Clamp off the vacuum hose to the PCV
valve. The engine speed should
decrease 100 RPM to indicate the loss
of the calibrated air leak into the intake
manifold. The vacuum gauge reading
should increase slightly indicating that
the vacuum leak has been plugged. If
this does not happen, replace the OCV
valve and/or replace any damaged,
plugged or loose hoses.
4) If the engine is idling too slow or is
rough, this may be caused by a clogged
PCV valve or hose. Do not adjust the
idle speed without first checking the
PCV system.
5) After installing a new PCV valve,
always adjust the idle speed, and if
possible, the idle air mixture. The
installation of the wrong valve may
cause too much vapor to flow through
the system if the calibrated bleed is too
large. This will lean out the air/fuel
mixture excessively. If the opening is
too small, the plugging effect will be
nullified, emissions will increase,
crankcase acids will form and oil leaks
may develop. Be sure you get the
correct PCV valve for your car.
EXHAUST GAS RECIRCULATION (EGR)
An Exhaust Gas Recirculation (EGR) sys-
tem is used on most modern engines to
reduce Oxides of Nitrogen (NOx) emis-
sions. During the combustion process,
nitrogen, which makes up 80 percent of
the air, will mix with oxygen at tempera-
tures above 2,500° F. During the combus-
tion process, temperatures in the
cylinders go well above 3,500° F
providing for the formation ideal condi-
tions for the formation of Nox. SYSTEM OPERATION
To reduce the formation of NOx, it is
necessary to lower the combustion
temperature. This is most often done by
introducing exhaust gases back into the
combustion chamber through the use of
an EGR valve. The EGR valve (FIGURE 6)
may be operated by ported vacuum from
above the throttle plates or by a sophisti-
cated control system that modulates the
amount of EGR depending on the temper-
ature of the coolant, ambient air tempera-
ture, engine speed or load.