Mercury Mariner 25HP 4-Stroke Outboard Service Manual 1997, Page 60Get this manual
Recommended Test (cont (1) (2) (3) (4) OVA TEST (Direct Voltage Adapter) OHM TEST (Resistance Testing) Replace Component and Retest Mechanical TesVRepair PROBLEMCONOITION
Timing Will Not Advance Probable Cause Low Oil PressureEngine Over Heating:timing retards and fluctuates, rpm will remain below 2000 rpm
Perform Test No3
(ECM) Engine Misfires At High RPM
Low Oil PressureEngine Over Heating:timing retards and fluctuates, rpm will remain below 2000 rpm
Ignition ColiHigh Tension Lead(s) Spark Plug Cap(s) 5k Resistor Spark Plug(s) (ECM) Unit Ground Connection:(ECM)Ignition coil
cstator
Engine Hard To Start Cold
Debris In Carburetor Enrichener Circuit Weak Spark Condition Throttle Plate In Open Position Weak Spark Condition Vapor Lock Low Oil PressureEngine Over Heating:timing retards and fluctuates, rpm will remain below 2000 rpm Stator Ignition CoilHigh Tension Lead(s)