Section 07 ENGINE MANAGEMENT (DI)
Subsection 02 (COMPONENT INSPECTION AND ADJUSTMENT)
Safety Lanyard Removed
Connect test probes to switch BLACK and
BLACK/YELLOW wires. Measure resistance,
there should be NO continuity (open circuit).
Connect one test probe to the WHITE/GRAY wire
and the other test probe to the switch terminal.
Measure resistance, it must be close to 0 ohm.
Connect one test probe to the BLACK wire and
the other test probe to the switch ring. Measure
resistance, it must be close to 0 ohm.
Safety Lanyard on Switch
Connect test probes to switch BLACK and
BLACK/YELLOW wires. Measure resistance,
it must be close to 0 ohm.
As the DESS switch also controls the signal wire
to the power supply cut-off relay, it should be
checked as described below.
Power Supply Cut-Off Relay Verification
When the safety lanyard is on its post, the relay al-
lows current to be supplied from the battery to the
RED/PURPLE wire which supplies the MPEM and
all the electrical components (except bilge pump
which is connected to battery power).
When the safety lanyard is NOT on its post, the re-
lay cuts the current supply from the battery to the
MPEM and the electrical components thus pre-
venting current drain that would slowly discharge
the battery.
Test the signal wire to the power supply cut-off
relay as follows:
Disconnect DESS switch wires.
Connect test probes to switch BLACK and
BLACK/PURPLE wires.
With safety lanyard NOT on its switch: Mea-
sure resistance. There should be NO continuity
(open circuit). Otherwise replace DESS switch.
With safety lanyard INSTALLED on its switch:
Measure resistance. There should be continuity.
Otherwise replace DESS switch.
If switch tests good in both checks, do the follow-
ing.
Disconnect the connector on electrical box.
Using a voltmeter, perform the following tests:
Connect test probes to the small RED wire on
the starter solenoid and on the RED/PURPLE wire
from the cut-off relay. Reading should be 0 V. Oth-
erwise, replace the cut-off relay.
Keeping the test probes on the same wires, con-
nect a jumper wire between the BLACK/PURPLE
wire from the cut-off relay and the battery ground.
Measure voltage. Reading should be 12 V. Oth-
erwise, check wiring and if it is good, replace the
cut-off relay.
If there is no current supply to the electrical com-
ponents while the DESS switch and the cut-off re-
lay test good, check the wiring harness. If it tests
good, the MPEM could be suspected. Try a new
one.
SPARK PLUGS
Disassembly
First unscrew the spark plug one turn.
Clean the spark plug and cylinder head with com-
pressed air then completely unscrew.
Heat Range
The proper heat range of the spark plugs is deter-
mined by the spark plugs ability to dissipate the
heat generated by combustion.
The longer the heat path between the electrode
tip to the plug shell, the hotter the spark plug op-
erating temperature will be — and conversely, the
shorter the heat path, the colder the operating
temperature will be.
A “cold” type plug has a relatively short insulator
nose and transfers heat very rapidly into the cylin-
der head.
Such a plug is used in heavy duty or continuous
high speed operation to avoid overheating.
The “hot” type plug has a longer insulator nose
and transfers heat more slowly away from its fir-
ing end. It runs hotter and burns off combustion
deposits which might tend to foul the plug during
prolonged idle or low speed operation.
372 smr2004-Complete Line Up
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