Pontiac Fiero 1988 Service Manual page 710

DRIVEABILITY AND EMISSIONS - FUEL INJECTION (PORT) 6E3 C13-1
SECTION C13
POSITIVE CRANKCASE VENTILATION (PCV)
CONTENTS
GENERAL DESCRIPTION C13-1 FUNCTIONAL CHECK OF PCV VALVE . C13-1
RESULTS OF INCORRECT OPERATION . . . . C13-1 ON-CAR SERVICE C13-2
DIAGNOSIS C13-1 PARTS INFORMATION C13-2
GENERAL DESCRIPTION
A positive crankcase ventilation (PCV) system is
used to provide more complete scavenging of
crankcase vapors. Fresh air from the air intake duct is
supplied to the crankcase, mixed with blow-by gases
and then passed through a PCV valve into the Air
Plenum (Figure C13-1).
The primary control is through the PCV valve
(Figure C13-1) which meters the flow at a rate
depending on manifold vacuum.
To maintain idle quality, the PCV valve restricts
the flow when intake manifold vacuum is high. If
abnormal operating conditions arise, the system is
designed to allow excessive amounts of blow-by gases
to back flow through the crankcase vent tube into the
air cleaner to be consumed by normal combustion.
RESULTS OF INCORRECT OPERATION
A plugged valve or hose may cause:
• Rough idle.
• Stalling or slow idle speed.
• Oil leaks.
• Oil in air cleaner.
• Sludge in engine.
A leaking valve or hose would cause:
• Rough idle.
• Stalling.
® High idle speed.
DIAGNOSIS
FUNCTIONAL CHECK OF PCV VALVE
If an engine is idling rough, check for a clogged
PCV valve or plugged hose. Replace as required. Use
the following procedure:
1. Remove PCV valve from rocker arm cover.
2. Run the engine at idle.
3. Place your thumb over end of valve to check for
vacuum. If there is no vacuum at valve, check for
plugged hoses or manifold port, or PCV valve.
Replace plugged or deteriorated hoses.
4. Turn "OFF" the engine and remove PCV valve.
Shake valve and listen for the rattle of check
needle inside the valve. If valve does not rattle,
replace valve.
With this system, any blow-by in excess of the
system capacity (from a badly-worn engine, sustained
heavy load, etc.) is exhausted into the air cleaner and
is drawn into the engine.
<=> C L E A N A I R
— V O L A T I L E O I L F U M E S
MIXTURE O f AIR AND FUMES
[ T l P C V VALVE
[TITO
THROTTLE BODY
[Tl
CRANKCASE VENT HOSE
[ T ] P C V VALVE HOSE
[ I ! T O
INTAKE MANIFOLD
5S 1725-6E
Figure CI 3-1 PCV Flow (Typical)