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Digital Pressure Meter
Troubleshooting Without a Computer Diagnostic System (CDS)
Troubleshooting without the CDS (Computer Diagnostic System) is limited to checking resistance on some of the sensors.
Typical failures usually do not involve the ECM. Most likely at fault are the connectors, set‑up, and mechanical wear.
•
The engine may not run or may not run above idle with the wrong spark plugs installed.
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Swap ignition coils to see if the problem follows the coil or stays with the particular cylinder.
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Any sensor or connection can be disconnected and reconnected while the engine is operating without damaging the ECM.
Disconnecting the crank position sensor will stop the engine.
IMPORTANT: Any sensor that is disconnected while the engine is running will be recorded as a fault in the ECM Fault
Hours.
•
If all cylinders exhibit similar symptoms, the problem is with a sensor or harness input to the ECM.
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If problem is speed related or intermittent, it is probably connector or contact related. Inspect connectors for corrosion,
loose wires or loose pins. Secure connector seating. If dielectric compound was used to protect the wire connections, the
dielectric compound must be removed.
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Inspect the harness for obvious damage: pinched wires, chaffing.
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Check fuel pump connections and fuel pump pressure.
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Secure grounds and all connections involving ring terminals. Coat grounds and ring terminals with Liquid Neoprene.
Tube Ref No.
Liquid Neoprene
25
Troubleshooting with the Computer Diagnostic System (CDS)
The ECM is designed that if a sensor fails, the ECM will compensate so that the engine does not go into an over‑rich condition.
Because of this, disconnecting a sensor for troubleshooting purposes may have no noticeable effect.
The CDS has been developed specifically to help technicians diagnose and repair Mercury Marine 2 and 4 cycle engines.
CDS G3 Diagnostic Tool Kit
90-8M0105568 eng MARCH 2016
Connects to the fuel system/manifold and can be used in conjunction with
Computer Diagnostic System (CDS).
5786
Description
91‑892651A01
Where Used
Grounds and ring terminals
8M0114141
© 2016 Mercury Marine
Troubleshooting and Diagnostics
Part No.
92- 25711 3
Page 3B-3
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