FUEL INJECTION DESCRIPTIONS AND SYSTEM OPERATION
SERVICE MANUAL NUMBER 24
By moving a conical valve known as a pintle, IN, toward the seat (to decrease air flow), or
OUT, away from the seat (to increase air flow), a controlled amount of air moves around the
throttle valve. If rpm is too low, more air is bypassed around the throttle valve to increase
it. If rpm is too high, less air is bypassed around the throttle valve to decrease it.
The ECM moves the IAC valve in small steps, called counts. These can be measured by
scan tool test equipment, which plugs into the DLC.
During idle, the proper position of the IAC valve is based on engine rpm. If the rpm drops
below specification and the throttle valve is 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 flow into the engine based on IAC valve
pintle position + throttle valve stop screws and PCV.
•
“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 idle air rate is set at the factory with stop screws. This setting allows
enough air flow by the throttle valves to cause the IAC valve pintle to be positioned a
calibrated number of steps (counts) from the seat during “controlled” idle operation.
If the IAC valve is disconnected and reconnected with the engine running, the idle
speed may be wrong. In this case, the IAC valve can be reset by doing the following:
turn off engine, wait ten seconds, and restart engine.
350
Mag MPI And Black Scorpion - Multi-Port Injection Components
FUEL PUMP ELECTRICAL CIRCUIT
When the ignition switch is turned to the RUN position, the ECM will turn ON the fuel pump
relay for two (2) seconds.
When the ignition switch is turned to the crank position, the ECM turns the fuel pump relay
ON causing the fuel pump to start.
If the ECM does not receive ignition reference pulses (engine cranking or running), it shuts
OFF the fuel pump relay, causing the fuel pump to stop.
Index
Page 5D-30
90-861327 OCTOBER 1999
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 305 CID, Mercury MerCruiser 350 CID |
| Model Year | 1998, 1999, 2000, 2001 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
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Marine readers have rated Mercury MerCruiser Engines Service Manual Number 24 GM V-8 305 CID 350 CID 4.0 out of 4.0 based on 1 product reviews. Great performance engine.
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