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Mercury MerCruiser MCM 7.4L MPI User Manual

Mercury MerCruiser MCM 7.4L MPI
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CHARGING SYSTEM
SERVICE MANUAL NUMBER 23
90-861326--1 MARCH 1999 Page 4C-11
Current Output Test
Perform this test to check if alternator is capable of producing rated current output, using
a 0-100 amp DC ammeter.
WARNING
Be sure that engine compartment is well-ventilated and that there are no gasoline
vapors present (during the test) to prevent the possibility of an explosion and/or a
fire, should a spark occur.
1. Disconnect negative (–) battery cable from battery.
2. Disconnect ORANGE lead from alternator output terminal and connect ammeter in
series between lead and output terminal. Connect positive (+) side of ammeter toward
output terminal.
3. Reconnect negative battery cable.
4. Remove coil wire from distributor cap tower and ground it to block. Turn on all accesso-
ries and crank engine over with starter motor for 15-20 seconds.
5. Turn off accessories and reinstall coil wire. Start engine and adjust engine speed to
1500-2000 rpm. Quickly observe ammeter. Reading should be at least 30 amps.
6. If reading is low, stop engine and connect a jumper wire between alternator output
terminal and regulator terminal. Repeat Steps 4 and 5.
7. If reading is now within specifications, diodes are faulty. Disassemble alternator and
replace rectifier as explained under “Alternator Repair,” following, to determine if fault
is in regulator or alternator.
8. If reading is still low with jumper wire connected, perform “Voltage Output Test,” follow-
ing, to determine if fault is in regulator or alternator.
72787
b
a
c
d
e
f
a-Output Wire - ORANGE
b-Ammeter (0-50 Amps)
c-Jumper Lead
d-Regulator Lead
e-Ground
f-Output Lead (Orange)
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Mercury MerCruiser MCM 7.4L MPI Specifications

General IconGeneral
BrandMercury
ModelMerCruiser MCM 7.4L MPI
CategoryEngine
LanguageEnglish

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