2 - 2 ECM and Sensors 5.0/5.7/6.0/8.1L
MEFI 4 - PCM
TYPICAL
SENSOR
ECM
VOLTAGE OUT
SIGNAL INPUT
4-24-91
MS 11697
Figure 2-1 - Three-Wire Sensors
TYPICAL
SENSOR
ECM
SENSOR
SIGNAL
SENSOR
GROUND
4-24-91
MS 11698
5V
Figure 2-2 - Two-Wire Sensors
Two-Wire Sensors
Figure 2-2 shows a schematic representation of a 2-wire
sensor. This sensor is basically a variable resistor in series
with a known-fi xed resistor within the ECM. By knowing
the values of the input voltage and the voltage drop across
the known resistor, the value of the variable resistor can
be determined. The variable resistors that are commonly
used are called thermistors. A thermistor’s resistance
varies with temperature.
General Description
The Marine Electronic Fuel Injection (MEFI) system is
equipped with a computer that provides the operator with
state-of-the-art control of fuel and spark delivery. Before
we discuss the computers on the Marine applications,
let’s discuss how computers use voltage to send and
receive information.
Computers and Voltage Signals
Voltage is electrical pressure. Voltage does not flow
through circuits. Instead, voltage causes current. Current
does the real work in electrical circuits. It is current, the fl ow
of electrically charged particles, that energizes solenoids,
closes relays and illuminates lamps.
Besides causing current fl ow in circuits, voltage can be
used as a signal. Voltage signals can send information by
changing levels, changing waveform (shape) or changing
the speed (frequency( at which the signal switches from
one level to another. Computers use voltage signals to
communicate with one another. The different circuits
inside computers also use voltage signals to talk to each
other.
There are two kinds of voltage signals, analog and digital.
Both of these are used in computer systems. It is important
to understand the difference between them and the different
ways they are used.
Analog Signals
An analog signal is continuously variable. This means that
the signal can be any voltage within a certain range.
An analog signal usually gives information about a condition
that changes continuously over a certain range. For
example, in a marine engine, temperature is usually
provided by an analog signal. There are two general types
of sensors that produce analog signals, the 3-wire and
the 2-wire sensors.
Three-Wire Sensors
Figure 2-1 shows a schematic representation of a 3-wire
sensor. All 3-wire sensors have a reference voltage, a
ground and a variable “wiper.” The lead coming off of the
“wiper” will be the signal to the Engine Control Module
(ECM). As this “wiper” position changes, the signal voltage
to the ECM also changes.
To Next Page
Loading...
Need help?
General
