Battery Precautions - Multiple Edi Engines - Mercury MerCruiser D2.8L D-Tronic Service Manual

SERVICE MANUAL NUMBER 22

Battery Precautions - Multiple EDI Engines

SITUATION
Alternators: Alternators are designed to charge the battery that supplies electrical power
to the engine that the alternator is mounted on. When batteries for two different engines are
connected, one alternator will supply all of the charging current for both batteries. Normally,
the other engine's alternator will not be required to supply any charging current.
EDI Engine Control Module (ECM): The ECM requires a stable voltage source. During
multiple engine operation, an onboard electrical device may cause a sudden drain of voltage
at the engine's battery. The voltage may go below the ECM's minimum required voltage.
Also, the alternator on the other engine may now start charging. This could cause a voltage
spike in the engine's electrical system.
In either case, the ECM could shut off. When the voltage returns to the range that the ECM
requires, the ECM will reset itself. The engine will now operate normally. This ECM shut
down usually happens so fast that the engine just seems to have misfired.
RECOMMENDATIONS
Batteries: Boats with multi-engine EDI power packages require each engine be connected
to its own battery. This ensures that the engine's Electronic Control Module (ECM) has a
stable voltage source.
Battery Switches: Battery switches should always be positioned so each engine is operat-
ing off its own battery. Do NOT operate engines with switches in BOTH or ALL position. In
an emergency, another engine's battery can be used to start an engine with a dead battery.
Battery Isolators: Isolators can be used to charge an auxiliary battery used only for acces-
sories. Isolators should not be used to charge the battery of another engine in the boat.
Generators: The generator's battery should be considered another engine's battery.
90-860074--1 FEBRUARY 2002
CHARGING SYSTEM
Page 4B-7