Kohler Kill Circuit

[aloha]

I am troubleshooting problems with my Scag powered by a Kohler 27 hp CH740 engine. One specific issue I have run into involves the engine's kill circuit. If I understand the service manual for the engine, the kill circuit works by grounding the ignition modules to prevent the spark plugs from being energized. And, if I understand the service manual correctly, if the kill circuit is disabled the engine, once started, will continue to run until stopped by some other method such as shutting of the fuel. If I have misunderstood the manual, please correct me.

My problem has been that the spark is being killed with the ignition switch in the run position as well as off position. I do have spark when the ignition switch is in the start position.

When I disconnect the wires identified in the wiring diagram as "kill" from the ignition modules I get no spark even when the ignition switch is in the start position. There is another wire to the ignition modules identified as "trigger" so I tried disconnecting those to see if the diagram had wire labels reversed, but got the same result--no spark at all. I have also tried disconnecting the white wire emerging from the spark advance module which the diagram labels as "kill" and get the same result--no spark, even in the start position.

If someone can correct my understanding of the kill circuit, or how to disable it, or make any sense of this, I will be most grateful. Thanks.

 

[taxidermist]

Hello,

I can come there in Dec. and fix it for you LOL.

I think you might have a problem in the key switch. I would pull the switch and use a tester and check it for a short.

Rob

 

[aloha]

Rob-
Thanks for the kind offer. You sure you can't catch the next flight out? My grass is growing and by December the jungle would win.

I, too, tend think it is a problem in the switch, although there also is an electronic module that does magic with the safety switches and might be the source of my problems (and seems to be untestable and is too expensive to buy on the off chance that it is the problem).

I have pulled the ignition switch and taken resistance readings across the 6 terminals with the switch in off, on, and start positions. Making sense of the readings is proving difficult because the Kohler wires have a different color scheme from the Scag wires, their connections seem buried deep within the bowels of the machinery, and whoever made the Scag wiring diagram thought it was good enough to show "engine" as a single point at which 7 wires connect. So, it is not clear to me what all the numbers mean.

If I was sure about the kill circuit I might be able to make some progress, if only to prevent it from killing the spark.

 

[taxidermist]

Its 95* here in Michigan so I think I would like to wait until we have 12" snow on the ground and its -10* before I get on the plane. LOL

Did you try this?

1. Locate the plug connectors where the wiring
harnesses from the engine and equipment are
joined. Separate the connectors and remove the
white 徒ill 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 the key switch,
wires, connections, safety interlocks, etc.

 

[aloha]

I can disconnect the kill wire just before it enters the speed advance module. When I do that I get no spark in either the start or on ignition switch positions, reconnect it and I get spark in the start position, but no spark in the on position.