Positive Crankcase Ventilation (Pcv) System; Fuel Evaporative Control System - Jeep cherokee 1989 Owner's Manual

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Positive Crankcase Ventilation (PCV) system

Refer to illustrations 2.5a and
1 The Positive Crankcase Ventilation (PCV) system reduces hydro-
carbon emissions by scavenging crankcase vapors. It does this by cir-
culating fresh air from the air cleaner through the crankcase, where
it mixes with blow-by gases and is then rerouted through a PCV valve
to the intake manifold.
2 The main components of the PCV system are the PCV valve, a
fresh air filtered inlet and the vacuum hoses connecting these two com-
ponents with the engine.
3 To maintain idle quality, the PCV valve restricts the flow when
the intake manifold vacuum is high. If abnormal operating conditions
(such as piston ring problems) arise, the system is designed to allow
excessive amounts of blow-by gases to flow back through the
crankcase vent tube into the air cleaner to be consumed by normal
combustion.
4 Checking and replacement of the PCV valve and filter is covered
in Chapter 1.
5
Later fuel-injected vehicles are equipped with a Crankcase Venti-
lation System (see illustrations). The CCV system performs the same
function as a conventional PCV system but does not use a vacuum
controlled valve.
6 A molded vacuum tube connects manifold vacuum to a grommet
on the top rear of the rocker arm cover (four-cylinder engine) or top
front of the cover (inline six-cylinder engine). The grommet contains
a calibrated orifice that meters the amount of crankcase vapors drawn
out of the engine. A fresh air supply hose from the air cleaner is con-
nected to the top front of the rocker arm cover (four-cylinder engine)
or the top rear of the cover (inline six-cylinder engine). When the engine
FROM AIR CLEANER
.
Crankcase Ventilation (CCV) system used on
fuel-injected inline six-cylinder engines
The Motor Manual Guy
Chapter 6 Emissions and engine control systems
.
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CCV AIR OUT
CCV AIR OUT
I
ORIFICE
is operating, fresh air enters the engine and mixes with the crankcase
vapors. Manifold vacuum draws the vaporlair mixture through the
metered orifice and into the intake manifold. The vapors are consum-
ed during combustion.
3

Fuel evaporative control system

Refer to illustrations 3.6a, 3.66, 3 . 6 ~ and 3.6d
General description
1 The fuel evaporative control system prevents the release of un-
burned hydrocarbons from liquid gasoline or fuel vapors
atmosphere. When the pressure in the fuel tank exceeds 3 psi, a pres-
sure relieflrollover valve opens, preventing excessive pressure build-up
in the tank and allowing the fuel vapors t o flow to an evaporative
canister, where they are absorbed by granules of an activated carbon
mixture.
2
When the vehicle is started, the fuel vapors stored in the canister
are drawn out of the canister and into the engine for combustion.
3
The evaporative canister inlet on fuel-injected vehicles is connected
to the fuel tank rolloveripressure relief valve(s) through a series of hoses
and tubes. The canister outlet is connected t o the air cleaner snorkel.
When the engine is operating, the canister purge valve draws fresh
air through the filter at the bottom of the canister, causing the stored
vapors t o be drawn from the canister and into the airstream in the air
cleaner snorkel.
4 A venturi in the air cleaner assembly creates a purge line vacuum
source. This venturi increases the speed of the intake air flowing by
the purge inlet slots in the venturi wall, which creates a low pressure
area at the inlet slots that draws vapors from the canister into the
Crankcase Ventilation (CCV) system used on
fuel-injected four-cylinder engines
INTAKE MANIFOLC
6-7
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into the
FROM