12251-ZV4-610 Honda SEE PART DETAILS - PRI; GASKET, CYLINDER HEAD (Honda Code 4537536).

Ignition systems can cause electrical shocks. Avoid contacting the ignition system components and wiring.Do not attempt to remove the transformers when the engine is operating. The transformers are grounded to the valve covers. Personal injury or death may result and the ignition system will be damaged if the transformers are removed during engine operation.
Turn the engine control OFF. Switch the engine circuit breaker OFF.
Illustration 1 g00929956
(1) Cover
(2) Connector
(3) Transformer
(4) Extension
(5) Spark plug
(6) Mounting flange for the transformer
Remove cover (1).
Disconnect the ignition harness from connector (2). Remove transformer (3) and extension (4) from the engine.
Inspect the body of transformer (3) and extension (4) for corrosion and/or for damage.
The extension has an internal O-ring seal for spark plug (5). Inspect the O-ring seal for damage.
The extension has an internal terminal for the spark plug. Inspect the terminal for looseness, for corrosion, and/or for damage. Insert an extra spark plug into the transformer and check the terminal for spring pressure.
The extension can be scratched and damaged with a wire brush. Do not use a wire brush on the extension.
Clean any deposits from the inside of the extension. Use a 6V-7093 Brush with isopropyl alcohol.
Illustration 2 g00754013
Symbol for a diode
Measure the primary circuit by checking the voltage of the diode.
Illustration 3 g00829100
Transformer connector for the ignition harness
(A) Terminal
(B) Terminal
(C) Unused
Set the multimeter to the diode scale. Connect the multimeter leads to terminals (A) and (B) on the transformer connector for the ignition harness. The polarity of the leads does not matter. Measure the voltage between the terminals and record the measurement.
Reverse the polarity of the probe and measure the voltage between the terminals again. One of the measurements is approximately 0.4 to 0.6 VDC. The other measurement indicates an open circuit.Voltage that is significantly outside of this range could indicate a problem with the transformer.
Measure the resistance of the secondary circuit.
Set the multimeter to the 40,000 Ohm scale. Measure the resistance between the terminal internal to the extension for the spark plug and mounting flange (6) for the transformer. If the resistance between the terminal for the spark plug and the mounting flange for the transformer is within the acceptable tolerance, proceed to Step 10.Resistance that is significantly outside of this range could indicate a problem with the transformer or with the extension.Note: The resistance of the secondary coil will vary with the temperature. The resistance depends on the transformer that is used. Illustration 4 shows the connection for the former transformers. Illustration 5 is a graph for the resistance of the former transformers. A reading that is within 1000 Ohms is acceptable.
Illustration 4 g01361976
Former transformer
(2) Connector
(6) Mounting flange for the transformer
Illustration 5 g00863850
Resistance versus temperature
(Y) Resistance in ohms
(X) Temperature in degrees Celsius (degree Fahrenheit) Note: The resistance of the secondary coil will vary with the temperature. The resistance depends on the transformer that is used. Illustration 6 shows the connection for the new transformers. Illustration 7 is a graph for the resistance of the new transformers. A reading that is within 1000 Ohms is acceptable.
Illustration 6 g01361978
New transformer
(2) Connector
(6) Mounting flange for the transformer
Illustration 7 g01170387
Resistance versus temperature
Switch the suspect transformer with a transformer from a different cylinder that is known to be good. Install the transformers.
Reset the control system. Clear any logged diagnostic codes.
Start the engine and operate the engine in order to generate a diagnostic code. If the problem follows the transformer, replace the transformer. Make sure that you use the correct transformer for the engine. Reset the control system. Clear any logged diagnostic codes.If the problem stays with the cylinder, there is a problem with the spark plug or with the electrical circuit for the transformer.For instructions on the electrical circuit, refer to the engine Troubleshooting manual.Spark Plug
If a diagnostic code is generated for the ignition transformer secondary circuit, the spark plug may need to be replaced. Misfire and a cold cylinder are other indications of a worn spark plug. Use the Caterpillar Electronic Technician (ET) to monitor the exhaust port temperatures in order to locate a cold cylinder.There is virtually no maintenance for the spark plug. The electrode gap is not adjustable. The resistance cannot be measured. Unless the holes in the precombustion chamber of the spark plug become plugged, no cleaning is required.For instructions on inspection and replacement of the spark plug, refer to the engine Operation and Maintenance Manual.