COVER 8U5007 - Caterpillar

Table 4
Troubleshooting Test Steps Values Results
3. Test the Primary Circuit of the Transformer
A. Check the primary circuit by measuring the voltage drop across the blocking diode.
B. Set the multi-meter to the diode scale. Connect the multi-meter leads across the terminals of the transformer connector (11). The polarity of the leads is not important for the first measurement. Record the voltage that is indicated by the meter.
Refer to Illustration 2.
C. Reverse the polarity of the multi-meter leads. Record the voltage that is indicated by the meter.
Primary Circuit Condition
Results: The transformer is OK.
One measurement indicates an open circuit.
The other measurement indicates approximately 0.450 V.
Proceed to Test Step 4.
Results: The transformer is NOT OK.
At least one of the measurements is incorrect.
Repair: Perform the following procedure:
1. Replace the ignition transformer. Ensure that the specified transformer for the specific engine application is used.
2. Before returning the engine to service, clear the logged diagnostic codes.
Illustration 2 g03359750
Test points at the ignition transformer (partial cutaway view)
(11) Test points at the input terminals for the primary circuit
(12) Test points for the secondary circuit
Table 5
Troubleshooting Test Steps Values Results
4. Test the Secondary Circuit of the Transformer
A. Measure the resistance of the secondary circuit.
The resistance of the secondary coil will vary with the temperature.
Refer to Illustration 3. A measured resistance that is within 1,000 Ohms is acceptable.
B. Set the multi-meter to the 40,000 Ohm scale. Connect the leads of the multi-meter between test points (12). Measure the resistance between the screw for the ground spring and the connector for the spark plug.
Refer to Illustration 2.
Secondary Circuit Condition
Results: The transformer is OK.
The measurement is within the acceptable tolerance.
Proceed to Test Step 5.
Results: The transformer is NOT OK.
The measurement is not within the acceptable tolerance.
Repair: Perform the following procedure:
1. Replace the ignition transformer. Ensure that the specified transformer for the specific engine application is used.
2. Before returning the engine to service, clear the logged diagnostic codes.
Illustration 3 g03359749
Resistance versus temperature for the 259-2078 Ignition Transformer Gp
Table 6
Troubleshooting Test Steps Values Results
5. Test the Spark Plug
A. Remove the electrical power from the engine.
B. Perform the following procedures according to the instructions in the engine Operation and Maintenance Manual.
a. Remove the spark plug from the cylinder head.
b. Inspect the spark plug.
c. Clean the spark plug.
C. Measure the spark plug resistance after the spark plug has been cleaned.
A standard Ohmmeter cannot be used for measuring the resistance of a used spark plug.
a. Use the 142-5055 Insulation Testing Gp (ELECTRICAL) to measure the resistance of the spark plug. Follow the warnings and instructions that are provided with the tool.
b. Connect the red lead of the tester to the terminal post. The spark plug ground tab may obstruct the placement of the testing group contact lead. You may need to connect a smaller lead to the center electrode. Then connect the black lead of the tester to the smaller lead.
c. Use the tester "20 KΩ" scale.
Spark Plug Condition
Results: The spark plug is OK.
The resistance is less than 10,000 Ohms.
Proceed to Test Step 6.
Results: The spark