Mariner Mercury 105/140 JET, Service Manual

Page: 243 / 797

3C-36 - FUEL SYSTEMS 90-824052R3 JUNE 2002
Detonation Sensor Check
IMPORTANT: When testing detonation control
system keep all test leads away from high
tension leads (i.e. spark plug lead, electrical
wiring etc.) to avoid false readings.
Purpose: This check will determine if sensor is
correctly signaling control module.
Procedure: STEP 1: Connect Digital Volt Meter
(from EFI Tester P/N 91-11001 A2) to
detonation sensor as shown. Red “V-
Ω
”
test lead to sensor terminal, black “com”
test lead to sensor housing (ground).
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STEP 2: Turn meter dial to 200 MV volts, AC posi-
tion and power switch in on position.
Place outboard in water.
STEP 3: Start and operate engine at idle speed.
STEP 4: Check meter reading. A typical reading
of .075 to .120 volts AC should be
present.
NOTE: As RPM increases volt readings will increase.
Results: If voltage reading is not within .075 to .120
volts AC replace detonation sensor. Torque
sensor to 144 Ib. in. (16.2 N·m).
If voltage reading is within .075 to .120 volts AC
perform check on detonation control module.
IMPORTANT: Handle detonation sensor with care
when testing or replacing. Rough handling could
cause undetectable internal damage causing
false readings to be transmitted to detonation
module.
Detonation Control Module Check
Purpose: This check will determine if control module
is correctly signaling ECM when signals are
received from sensor.
Procedure: STEP 1: Insert probe (a) (i.e. paper
clip) to gray/white wire connector (b).
Connect digital volt meter (from EFI tester
91-11001A2) positive clip (c) to probe and
ground clip to engine ground (d) as
shown.
d
a
b
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c
a - Probe
b - Connector
c - Positive Clip
d - Ground Clip
STEP 2: Turn meter dial to 20 volts DC position
and power switch in ON position. Place
outboard in water.
STEP 3: Start and operate engine at idle.
STEP 4: Check meter reading. A reading
between 0.30 to 0.70 volts DC should be
attained.
STEP 5: Increase engine speed (with engine in
gear) between 3000-4000 RPM. Check
meter reading. A typical reading should
be .01 volts DC.
Results: If meter reading is .30 to .70 volt DC at idle
and .01 volts DC at 3000-4000 RPM, detona-
tion control unit is functioning properly (no
detonation occurring).
If voltage reading does not fall within range (.30 to .70
volts DC) at idle, control module may be bad.
If voltage reading is above .01 volts DC and between
1.0 to 6.6 volts DC at 3000 to 4000 RPM detonation
is occurring. A constant voltage of 6.6 volts DC would
indicate bad detonation control module.