Mercury MerCruiser D2.8L D-Tronic Service Manual page 490

DESCRIPTION
FUEL TEMPERATURE SENSOR
The Fuel Temperature Sensor is a thermistor (a resistor which changes value based on
temperature) immersed in the fuel inside the upper chamber of the fuel pump. It is not a
serviceable item. Low fuel temperature produces a high resistance, while high temperature
causes low resistance.
The ECM supplies a fixed current to the pump through a resistor in the ECM and measures
the voltage. The voltage will be high when the fuel is cold, and low when the fuel is hot. By
measuring the voltage, the ECM knows the fuel temperature.
A failure in the fuel temperature circuit should set Code P0180. Remember, this code
indicates a failure in the fuel temperature sensor circuit, so proper use of the chart will lead
to either repairing a wiring problem or determining the failure is the fuel pump. However, it
is not suggested that the pump be replaced for this failure unless the customer complains
of related driveability problems.
ENGINE RPM SPEED SENSOR
The Engine rpm Speed sensor is an induction-type pulse generator which scans the leading
edge of the flywheel. Four notches (drillings) serve to sense the engine speed. The resulting
change in magnetic flux induces an AC voltage signal which is evaluated by the ECM. The
ECM processes the signal to establish TDC and the crankshaft position relative to TDC.
A failure in the Engine RPM Speed sensor circuit should set a Code P0725.
Page 5A-24
a - RPM Sensor
b - Electrical Connector
a
b
90-860074--1 FEBRUARY 2002
SERVICE MANUAL NUMBER 22
75311