Mariner Mercury 105/140 JET, Service Manual

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90-824052R3 JUNE 2002 ELECTRICAL - 2A-13
Ignition Troubleshooting
Multimeter/DVA Tester 91-99750A1
WARNING
DANGER - HIGH VOLTAGE/SHOCK HAZARD! Do
Not touch ignition components and/or metal test
probes while engine is running and/or
“cranked.”
Test Sequence
1-A. With DVA set @ 400VDC scale, check
primary input voltage to coils. (See Test Chart,
following.)
51843
DVA RED DVA BLK 400 RPM 1000
RPM 3000
RPM
Coil (+) Coil (–) 90 - 145 125 - 175 175 - 240
1. If voltage readings to coil(s) are BELOW specifi-
cation, proceed with Step 2-A.
2. If voltage readings to coil(s) are WITHIN specifi-
cation, proceed with Step 1-B.
1-B. Check coils for spark. [Connect Spark Gap
Tester (91-63998A1) between coil high voltage
tower and spark plug.]
1. If no spark or weak spark, COIL is bad.
2. If spark is OK, proceed with Step 1-C.
1-C. If Steps 1-A and 1-B check OK, replace spark
plugs.
If problem still is evident after replacing spark plugs,
proceed with Step 1-D.
1-D. If Steps 1-A, 1-B and 1-C check OK, check
ignition timing.
1. If ignition timing DOES NOT check to specifica-
tion (sudden and unexplained timing change),
check trigger advance linkage for loose or broken
parts and check trigger magnet ring in flywheel
(affixed to flywheel hub) for tightness and/or shift
in position.
2. If ignition timing is UNSTABLE (timing jumps
around, at “cranking” speed and/or low RPM),
proceed to Step 5-A.
3. If ignition timing checks to specification and
engine still does not run or runs poorly, trouble
exists with fuel system or engine mechanical.
2-A. With meter set @ 400DVA scale, check
switch box “stop” circuit. (See Test Chart,
following.)
51838
DVA RED DVA BLK 400 RPM 1000
RPM 3000
RPM
BLK/YEL GROUND 200 - 300 225 - 400 225 - 400
1. If reading is BELOW specification, proceed with
Step 2-B.
2. If reading is ABOVE specification, either the trig-
ger or switch box is bad (test trigger as out- lined
in Outboard Service Manual; if trigger checks to
specification replace switch box and repeat
check).
3. If reading is WITHIN specification, proceed with
Step 3-A.