FUEL INJECTION DESCRIPTIONS AND SYSTEM OPERATION
SERVICE MANUAL NUMBER 24
Open or Grounded REF HI Line - This line provides the ECM with engine speed informa-
tion. If this line is open or grounded, the ECM will not know that the engine is cranking or
running and will not run.
Open or Grounded REF LO Line - This wire is grounded in the ignition module and pro-
vides a reference ground from the ignition module to the ECM. The ECM compares refer-
ence ground with reference high voltage. If this circuit is open, or grounded at any other loca-
tion than through the module, it may cause poor performance.
Fuel Metering System
General Description
The function of the fuel metering system is to deliver the correct amount of fuel to the engine
under all operating conditions. The fuel is delivered to the engine by individual fuel injectors
mounted in the intake manifold near each cylinder (MPI) or from two injectors mounted on
top of the intake manifold (EFI).
Cool Fuel Systems
This system was used on later MerCruiser MEFI-1, MEFI-2 and MEFI-3 ECM engines. This
system has a fuel cooler and the electric fuel pump inside a box on the lower, port side of
the engine. The fuel regulator for this system is mounted on the fuel cooler.
Early versions of the MEFI-1 systems had a second regulator mounted in the fuel rail. This
regulator does not control system fuel pressure. It is used to dampen fuel system pulsation
only. Later versions of the MEFI-1 and the MEFI-3 have this regulator removed from the fuel
rail.
Modes of Operation
The ECM looks at voltages from several sensors to determine how much fuel to give the
engine. The fuel is delivered under one of several conditions, called modes. All the modes
are controlled by the ECM and are described below.
STARTING MODE
When the ignition switch is turned to the crank position, the ECM turns ON the fuel pump
relay and the fuel pump builds up pressure. The ECM then checks the Engine Coolant Tem-
perature (ECT) sensor and Throttle Position (TP) sensor and determines the proper air/fuel
ratio for starting. The ECM controls the amount of fuel delivered in the starting mode by
changing how long the injectors are turned ON and OFF. This is done by pulsing the injectors
for very short times.
CLEAR FLOOD MODE
If the engine floods, it can be cleared by opening the throttle half way (50%). The ECM dis-
continues fuel injector pulsation as long as the throttle is between 50 to 75 % and the engine
rpm is below 300. If the throttle position becomes more than 75% or less than 50%, the ECM
returns to the starting mode.
Index
Page 5D-24
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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