Fuel Injector; Air And Coolant Temperature Sensors; Fuel Pressure System - Westerbeke 6.5 MCG Service Manual

COMPONENT TESTING
AIR AND COOLANT TEMPERATURE SENSORS
Th~e
two sensors
con~
as their sensing.elements
identical negative temperature coefficient (NrC)
thermistors whose internal resistance inversely changes to a
change in temperature (i.e., temperature increase, resi'S- ·
tance decrease). The thennistors nominal resistance value
at
no
F (25° C) is 10,000 ohms. When the ECU is in an
on
state, the thennistors (-) lead is connected to ground,
and its (
+)
lead is connected to the ECU and then through
a fixed series 10,000 ohm resistor to the +5V power
source. Therefore, the voltage at the thennistors (
+)
lead
should be approximately +2.5 volts at a temperature of
no
F and decreases to a voltage of approximately +.25V at
220° F. The voltage - temperature relationship however, is
not linear over this range and therefore it should only serve
as an indicator that the thermistor is functioning.
Generally, the thermistor may be a:ssumed·to be good if
there is a perceptual· resistance change for a corresponding
temperature over -the indicated range, otherwise replace the
sensor.
FUEL INJECTOR
The fuel injector has no polarity and operates on 12 VDC.
The coil resistance is typically in the order of 14 to 16 ohms .
.. The positive wire to the injector is supplied power through
the contacts of relay K2, which is off when the engine is not
running. To test the injector, disconnect its cable connector
and connect a ground wire to one of its input pins. Connect
a wire from a point of B+ and repeatedly touch the other
input pin. When touched, a low audible click should be
perceptible; if not, resistance test the coil. If okay, the injector.
may be assumed to be functioning electrically. However it ·
could be clogged. If in doubt, replace the injector.
A LOW AUDIBLE:
CLICK SHOULD
BE HEARD.
TESTING SYSTEM FUEL PRESSURE
Connect a fuel pressure test gauge to the Schrader valve on
the throttle body as shown and run the engine. Pressure
readings should indicate 35 • 40 psi. · .
Pressure gauge kit MT337B "SNAP -ON-TOOL" is specifi-
cally d,esigned for fast accurate testing of fuel pressure for
. Schrader test ports.
56
THE AIR TEMPERATURE SENSOR IS LOCATED
IN THE LOWER PART OF THE AIR INTAKE HOUSING.
~~
THE COOLANT TEMPERATURE SENSOR IS LOCATED
AT THE LOWER REAR OF THE INTAKE MANIFOLD
ABOVE AND TO THE LEFT OF THE OIL FILTER.
TEMPERATURE SENSORS
Resistance Values (at room temperature)
Air Temperature Sensor -
to,ooon
Coolant Temperature Sensor -
to,ooon
TESnNG RESISTANCE
TESTING FUEL
PRESSURE