PleasureCraft Engine Group 5.0L, Руководство по диагностике

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3B - 6 Fuel Metering System 6.0L
MEFI 4 - PCM
Figure 3-8 - Flange Mounted Type IAC Valve
Figure 3-7 - IAC Valve Air Flow Diagram
1 IDLE AIR CONTROL (IAC) VALVE
2 THROTTLE BODY ASSEMBLY
3 THROTTLE VALVE
4 IAC VALVE PINTLE
A ELECTRICAL INPUT SIGNAL
B AIR INLET
RS 22193
A
1
2
4
3
B
8-25-94
1 O-RING - IAC VALVE
2 IAC VALVE ATTACHING SCREW
A DISTANCE OF PINTLE EXTENSION
B DIAMETER OF PINTLE
B
A
2
1
RS 22181
➤
➤
➤
➤
8-24-94
Diagnosis
If the Engine Cranks But Will Not Run or immediately
stalls, Table A-3 of the Diagnosis section must be used
to determine if the failure is in the ignition system or the
fuel system.
On-Board Service
Caution:
To reduce the risk of fi re and personal injury, relieve
fuel system pressure before servicing fuel system
components.
After relieving fuel pressure, a small amount of fuel may
be released when servicing fuel lines or connections.
To reduce the chance of personal injury, cover fuel
line fi ttings with a shop towel before disconnecting
to catch any fuel that may leak out. Place the towel
in an approved container when disconnection is
completed.
•
“Controlled” idle speed is programmed into the ECM,
which determines the correct IAC valve pintle position
to maintain the desired idle speed for all engine
operating conditions and loads.
•
The minimum air rate is set at the factory with a stop
screw. This setting allows enough air fl ow by the throttle
plates to cause the IAC valve pintle to be positioned
at a calibrated number of steps (counts) from the seat,
during “controlled” idle operation. This minimum air
rate setting should not be altered by turning the stop
screw or bending the linkage. Improper idle control
will result.
Idle Air Control (IAC) Valve
The purpose of the IAC valve assembly (Figures 3-7 and
3-8) is to control engine idle speed, while preventing stalls
due to changes in engine load.
The IAC valve, mounted to the throttle body, controls
bypass air around the throttle plates (Figure 3-7). By
moving a conical valve known as a pintle, IN, towards the
seat (to decrease air fl ow); or OUT, away from the seat (to
increase air fl ow), a controlled amount of air moves around
the throttle plates. If RPM is too low, more air is bypassed
around the throttle plates to increase it. If RPM is too
high, less air is bypassed around the throttle plates to
decrease it.
The ECM moves the IAC valve in small steps. These can
be monitored by scan tool test equipment, which plugs into
the Data Link Connector (DLC).
During idle, the proper position of the IAC valve is calculated
by the ECM, based on battery voltage, coolant temperature
and engine RPM. If the RPM drops below specifi cation
and the throttle plates are closed, the ECM senses a
near stall condition and calculates a new valve position
to prevent stalling.
•
Engine idle speed is a function of total air fl ow into
the engine based on IAC valve pintle position plus
throttle plates opening.