Mercury MerCruiser Service Manual page 273

Table of Contents
Troubleshooting With a Vacuum Gauge............................3C-2
Vacuum Gauge Troubleshooting Guide..................... 3C-2
Measuring Vacuum............................................................3C-3
Mechanical Engine Noise.................................................. 3C-3
Used Spark Plug Analysis................................................. 3C-4
Normal Condition........................................................3C-4
Chipped Insulator....................................................... 3C-5
Wet Fouling (Oil Deposits)..........................................3C-5
Cold Fouling............................................................... 3C-5
Overheating................................................................ 3C-6
High Speed Glazing....................................................3C-6
Scavenger Deposits................................................... 3C-6
Preignition Damage.................................................... 3C-7
Reversed Coil Polarity................................................ 3C-7
90-8M0099748 eng DECEMBER 2015
Engine Mechanical
Section 3C - Engine Troubleshooting
Splashed Deposits......................................................3C-7
Mechanical Damage...................................................3C-8
Piston Inspection............................................................... 3C-8
Starter Motor Will Not Crank Engine, or Cranks Slowly.....3C-9
Engine Will Not Start or Is Hard to Start.......................... 3C-10
Engine Runs Rough, Misses, or Backfires...................... 3C-10
Poor Performance............................................................3C-10
Engine Overheat..............................................................3C-10
Low Engine Temperature................................................ 3C-11
Low Engine Oil Pressure................................................. 3C-11
Water in the Engine......................................................... 3C-11
Important Information............................................... 3C-11
Compression Gauge Testing........................................... 3C-12
Leak-Down Testing..........................................................3C-12
© 2016 Mercury Marine
Engine Troubleshooting
Page 3C-1
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