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GM Marine EFI
Page 16
Service Mode Function (MEFI-1 thru MEFI-4 ECMs Only)
The Service Mode function is primarily used to set an engine’s base spark timing.
This function applies to engines equipped with a standard distributor. It is not
used on engines with Distributorless Ignition Systems (DIS) or those employing
a HVS distributor (i.e. engines equipped with Cam and Crank sensors).
Upon selecting the Service Mode menu option the currently active mode will be
displayed and you will have the choice of selecting either the Normal or Service
Modes. Simply select the desired mode then continue on to perform other scan-
ner functions if necessary. The “Service” mode will stay activated until changed
by entering the Service Mode function again and selecting a different mode or by
disconnecting the scan tool.
Special note for twin engine systems:
In order for the Service Mode to function properly on twin engine systems you
must have the scan tool attached to the Diagnostic Connector on the engine
being serviced.
Power Balance Test (MEFI-4 thru MEFI-6 ECMs Only)
The Power Balance Test is designed to assist a technician in finding a problematic
cylinder. This test commands the ECM to disable the spark output, or on some
systems both spark and fuel, to a selected cylinder thereby causing that cylinder
to misfire (not produce power). This test must be enabled by the engine manu-
facturer. Upon selecting the Power Balance Test the scan tool will query the ECM
to see if the test is available.
The objective of this test is to determine whether or not disabling a particular
cylinder will cause a drop in engine RPM. If a cylinder is disabled and the RPM
remains the same it is likely that the disabled cylinder is problematic and not
producing power under normal operating conditions. Please refer to the engine
manufacturer’s service literature for more information on this test.
• IMPORTANT: This test should be performed with the engine running
at approximately 1500 rpm, at normal operating temperature and under
moderate load.
• Do not attempt to drive the boat while performing this test.
• Follow all engine and boat manufacturer’s safety precautions and stay
clear of all moving engine components.
• Refer to the engine manufacturer’s service manual for special notes on
performing this test.