HOSE 1786557 - Caterpillar

If an ignition transformer is suspect, use the following procedure to check the transformer:
Ignition systems can cause electrical shocks. Avoid contacting the ignition system components and wiring.Do not attempt to remove the valve covers 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 valve covers are removed during engine operation. The engine will not operate without the valve covers.
Turn the engine control switch to the OFF/RESET position. Switch the circuit breaker for the engine OFF.
Remove the valve cover of the suspect cylinder.
Pulling on the wiring harness may break the wires. Do not pull on the wiring harness.
Disconnect the ignition harness from the transformer. Remove the transformer from the engine.
Illustration 1 g01257165
(1) Screw
(2) Ground spring
(3) Seal
(4) Spacer
(5) Terminal for the spark plug
(6) Extension
(7) O-ring seal
Inspect the body of the transformer and ground spring (2) for corrosion and/or damage. Verify that screws (1) for the ground spring are secure. Note: Punch through causes misfire in the engine that does not generate a diagnostic code.
Check the extension near spacer (4) for signs of punch through (pin holes) and/or arcing.
Inspect seal (3) and also inspect O-ring seal (7) inside the extension for damage.
Remove O-ring seal (7). Inspect terminal (5) inside the extension for looseness, corrosion, and/or damage. Insert a spark plug into the transformer and check for spring pressure of terminal (5).
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 g01257170
(1) Screw
(5) Terminal for the spark plug
(8) + pin
(9) - pin
Measure the voltage of the diode for the primary circuit.
Illustration 3 g00754013
Symbol for a diode
Set the multimeter to the diode scale. Measure the voltage between positive pin (8) and negative pin (9).
Reverse the polarity of the probe and measure the voltage between the pins again. For the diode of the primary circuit, the correct voltage between the positive pin and the negative pin is approximately 0.450 VDC. When the polarity is reversed, there is no reading.
Measure the resistance of the secondary circuit.
Set the multimeter to the 40,000 Ohm scale. Measure the resistance between screw (1) for the ground spring and terminal (5) for the spark plug. Note: The resistance of the secondary coil will vary with the temperature. Illustrations 4 and 4 demonstrate the relationship between the secondary coil's resistance and the temperature. A reading that is within 1000 ohms is acceptable.Illustration 4 is a graph for the resistance of the transformers.
Illustration 4 g01170387
Switch the suspect transformer with a transformer from a different cylinder that is known to be good. Install the transformers. Install the valve covers.