Kohler COMMAND CH18-745 User Manual download pdf (Page 124)

8.7

Section 8

Electrical System and Components

The pulse generated by the input coil of the ignition

module (L1, Figure 8-5) is fed to the input of the

conditioning circuit. The conditioning circuit shapes this

pulse, putting it in a useable form for the additional

circuits. This pulse starts the charge pump, which

charges a capacitor in a linear fashion that can be

directly related to the engine speed. At the same time

the pulse resets the delay circuit for length of the pulse

width. The comparator is off during this period and no

output is generated. As soon as the original pulse

drops back to zero, the capacitor in the delay circuit

begins to charge.

When the charge on the delay capacitor exceeds the

charge on the charge pump capacitor the comparator

changes state, activating the pulse generator. This

pulse turns “ON” the CD ignition module

semiconductor. Energy is then transferred to the

secondary of the output transformer (T1, Figure 8-5).

The high voltage pulse generated here is delivered to

the spark plug, causing arcing of the spark gap and

igniting the fuel-air mixture in the combustion chamber.

As the trigger pulse is generated, all associated

circuits are reset, their capacitors discharged. The

longer it takes the delay circuit to surpass the charge

pump capacitor voltage, the later the trigger pulse will

occur, retarding the timing accordingly.

Troubleshooting CD Ignition Systems

The CD ignition systems are designed to be trouble

free for the life of the engine. Other than periodically

checking/replacing the spark plugs, no maintenance or

timing adjustments are necessary or possible.

Mechanical systems do occasionally fail or break

down, however, so the following troubleshooting

information is provided to help you get to the root of a

reported problem.

CAUTION: High-Energy Electric Spark!

The CD ignition systems produce a high-energy

electric spark, but the spark must be discharged, or

damage to the system can result. Do not crank or run

an engine with a spark plug lead disconnected. Always

provide a path for the spark to discharge to ground.

Reported ignition problems are most often due to poor

connections. Before beginning the test procedure,

check all external wiring. Be certain all ignition-related

wires are connected, including the spark plug leads.

Be certain all terminal connections fit snugly. Make

sure the ignition switch is in the run position.

NOTE: The CD ignition systems are sensitive to

excessive load on the kill lead. If a customer

complains of hard starting, low power, or

misfire under load, it may be due to excessive

draw on the kill circuit. Perform the appropriate

test procedure.

Test Procedure for Standard (Fixed Timing) CD

Ignition System

Isolate and verify the trouble is within the engine ignition

system.

1. Locate the plug connectors where the wiring

harnesses from the engine and equipment are

joined. Separate the connectors and remove the

white “kill” lead from the engine connector. Rejoin

the connectors and position or insulate the kill lead

terminal so it cannot touch ground. Try to start**

the engine to verify whether the reported problem

is still present.

a. If the problem is gone, the electrical

system on the unit is suspect. Check thekey

switch, wires, connections, safety interlocks,

etc.

b. If the problem persists the condition is

associated with the ignition or electrical

system of the engine. Leave the kill lead

isolated until all testing is completed.

**NOTE: If the engine starts or runs during any of the

testing, you may need to ground the kill lead

to shut it down. Because you have interrupted

the kill circuit, it may not stop using the switch.

2. Test for spark on both cylinders with Kohler ignition

tester, SPX Part No. KO1046 (formerly Kohler Part

No. 24 455 02-S). Disconnect one spark plug lead

and connect it to the post terminal of the tester.

Connect the clip to a good ground, not to the spark

plug. Crank the engine and observe the tester

spark gap. Repeat the procedure on the other

cylinder. Remember to reconnect the first spark

plug lead.

a. If one side is not firing, check all wiring,

connections, and terminations on that side. If

wiring is okay, replace ignition module and

retest for spark.

b. If the tester shows spark, but the engine

misses or won’t run on that cylinder, try a new

spark plug.

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Kohler COMMAND CH18-745 User Manual Page 124

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