Mercury 225 EFI Service Manual page 247

FUEL INJECTION
ENGINE HEAD TEMPERATURE SENSOR (PORT AND STARBOARD CYLINDER HEAD)
The Engine Head Temperature Sensors provide the ECM signals related to engine tem-
perature, to determine level of fuel enrichment during engine warm up. The ECM is receiv-
ing information at all engine temperatures. Disconnecting the temperature sensors or tem-
perature sensor failure will cause the ECM to revert to a default temperature source of 32
F (0 C). The temperature sensors can be monitored with the DDT.
THROTTLE POSITION SENSOR (TPS)
The TPS transmits throttle angle information to the ECM which varies the injector pulse
width accordingly. Should the sensor fail, the dash mounted CHECK ENGINE light will illu-
minate and the warning horn will sound. RPM will be reduced by the ECM. The TPS is not
adjustable. TPS settings can be monitored with the Digital Diagnostic Terminal. Voltage
change should be smooth from idle to wide open throttle. If voltage change is erratic, the
TPS is defective.
IGNITION Throttle Position Sensor
SYSTEM @ Idle
@ W.O.T.
WATER SENSING SYSTEM
The system consists of a water separating fuel filter (port side powerhead) and a sensing
probe (bottom of filter).
WATER SENSING SYSTEM FUNCTION
1. The filter separates the accumulated water from the fuel.
2. A voltage is always present at sensing probe. When water reaches top of probe it com-
pletes the circuit to ground.
3. The completed circuit activates the warning horn which intermittantly sounds.
The system can be tested by disconnecting the TAN wire from sensor probe and holding
to a good engine ground connection for 10 seconds.
Page 3B-18
0.19 – 1.0 vdc
3.45 – 4.63 vdc
90-884294 OCTOBER 2001