MULTI-PORT FUEL INJECTION DESCRIPTIONS AND SYSTEM OPERATION
SERVICE MANUAL NUMBER 23
Engine Control Module (ECM)
The Engine Control Module (ECM) is the control center of the fuel injection system. It
constantly monitors information from various sensors, and controls the systems that affect
engine performance.
The ECM also performs a diagnostic function check of the system. It can recognize
operational problems and store a code or codes which identify the problem areas to aid the
technician in making repairs.
72801
Electronic Control Module (ECM) - MEFI 1 or MEFI 2 Shown, MEFI 3 Similar
ECM FUNCTION
The ECM supplies 5 or 12 volts to power various sensors or switches. This is done through
resistances in the ECM which are so high in value that a test light will not light when
connected to the circuit. In some cases, even an ordinary shop voltmeter will not give an
accurate reading because its resistance is too low. Therefore, the use of a 10 megohm
input impedance digital voltmeter is required to assure accurate voltage readings.
MEMORY
There are three types of memory storage within the ECM: ROM, RAM and EEPROM.
ROM
Read Only Memory (ROM) is a permanent memory that is physically soldered to the circuit
boards within the ECM. The ROM contains the overall control programs. Once the ROM is
programmed, it cannot be changed. The ROM memory is non-erasable, and does not need
power to be retained.
RAM
Random Access Memory (RAM) is the microprocessor “scratch pad.” The processor can
write into, or read from, this memory as needed. This memory is erasable and needs a
constant supply of voltage to be retained.
EEPROM
Electronic Erasable Programmable Read Only Memory (EEPROM) is the portion of the
ECM that contains the different engine calibration information that is specific to each marine
application.
Page 5B-18
90-861326--1 MARCH 1999
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 454 CID, Mercury MerCruiser 502 CID |
| Model Year | 1998, 1999, 2000, 2001 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
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