System Diagnosis - Undercharged Battery

TOOL REQUIRED:
J 39200 Digital Multimeter

An undercharged battery is usually characterized by slow cranking or by a dark battery hydrometer. If this condition exists, check the following items for a cause.
1. Determine that the uncharged condition is not the result of leaving accessories on for extended periods without charging the battery.
2. Check the drive belt for proper tension. Refer to Generator Replacement.
3. If a battery fault is suspected, refer to Diagnosis in Battery. Testing and Inspection
4. Inspect the wiring for faults. Check that all connections are clean and tight. Also check that any bulkhead connectors are tight and undamaged. Battery cable connections at battery, starter and engine ground points should also be checked.

Regulator Setting Voltage - Voltage Vs. Temperature:

5. With all accessories turned off, connect a J 39200. Run the engine at a moderate speed and check the voltage. Some consideration should he given to the temperature to which the generator is exposed during this test. As the temperature of the regulator case in the generator increases, the voltage output will decrease. The standard setting for the voltage regulator is 14.2 to 14.8 volts at 25°C (77°F). Under normal conditions, therefore, operating voltage should always he at least 13.5 volts. If the voltage is 13.5 volts or more, proceed to Step 6. If the voltage is less than 13.5 volts, remove the generator. Refer to Generator Replacement.
6. If Steps 1 through 5 have not uncovered the cause of the symptom, perform the following generator test:
A. Disconnect the negative (-) battery cable.
B. Remove the rubber protector, nut and generator B terminal wires.
C. Connect an ammeter between the generator and the disconnected wire. Connect the ammeter black lead to the wire and the ammeter red lead to the generator.
D. Connect a J 39200 between the generator B terminal and chassis ground.
E. Start and run the engine at 2000 RPM. turn all accessories and high-beam headlamps on. turn the blower to high. Ground the generator F terminal with a screwdriver.
F. Adjust engine speed, as required, to obtain the maximum current output.
G. If the current output is within 10 amperes of the maximum rating and the voltage reading is 13.5 to 16.0 volts, the generator is not faulty and is not the cause of an undercharged battery condition. Refer to the Generator Specifications. If the current output is not within 10 amperes of the maximum rating or the voltage reading is less than 13.5 volts, remove the generator.