Pontiac Fiero 1988 Service Manual page 578

DRIVEABILITY AND EMISSIONS - FUEL INJECTION (TBI) 6E2-C13-1
SECTION C13
POSITIVE CRANKCASE VENTILATION (PCV)
CONTENTS
G E N E R A L DESCRIPTION C I 3 - 1 FUNCTIONAL CHECK OF PCV VALVE . . . . .
C13-1
D I A G N O S I S
CI 3-1
O N - C A R S E R V I C E C 1 3 - 2
RESULTS OF INCORRECT OPERATION C13-1 P A R T S I N F O R M A T I O N C 1 3 - 2
GENERAL DESCRIPTION
A positive crankcase ventilation (PCV) system is
used to consume crankcase vapors in the combustion
process instead of venting to atmosphere. Fresh air
from the air cleaner is supplied to the crankcase,
mixed with blow-by gases and then passed through a
positive crankcase ventilation (PCV) valve into the
intake manifold (Figure C13-1).
The primary control is through the PCV valve
(Figure C13-2) 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.
DIAGNOSIS
RESULTS OF INCORRECT OPERATION
r
A plugged valve or hose may cause:
© Rough idle.
• Stalling or slow idle speed.
® Oil leaks.
< § Oil in air cleaner.
• Sludge in engine.
o A leaking valve or hose would cause:
® Rough idle.
• Stalling.
• High idle speed.
F U N C T I O N A L CHECK OF P C V V A L V E
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 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.
Proper operation of the PCV system is dependent
upon a sealed engine. If oil sludging or dilution is
noted, and the PCV system is functioning properly,
check engine for possible cause and correct to ensure
that system will function as intended.
[T1
P C V V A L V E
[T]
C R A N K C A S E V E N T H O S E
f T l A I R C L E A N E R [ T ] P C V V A L V E H O S E
4 8 1 1 5 2 - 6 E
Figure C13-1 - PCV Flow - Typical