Kohler 15.5 Engine Troubles

I have a Craftsman Tractor with a Kohler 15.5 hp engine in it. It runs and cuts fine for about an hour and then it always stalls out and dies. If I let it sit for an hour or so it starts up and will run for another 20 min and then does the same thing. It's gotten to the point where it takes me all day to cut a two acre lawn because I always have to let it sit, cut a little, and then let it sit, etc. Also, when it starts up after this happens the engine will "pulse" so it sounds similar to a car engine if you kept reving it. I've had it in the shop lots of times, but they can't re-create the problem because they're not cutting the lawn with it. They keep telling me nothing's wrong with it. Any ideas? Throttle problems?

 

Without the advantage of hearing it firsthand, it will be difficult to diagnose. But, I'd say you have an ignition related problem. The next time you mow have a spare spark plug in your pocket. The moment it quits, hop off the mower, open the hood, remove the spark plug wire from the spark plug, insert the spare plug into the plug wire, lay the plug on a metalic part of the engine to ground it, set your controls as you would to start the engine, engage the parking brake (this will allow you to be off the seat and crank over the engine), turn the key to spin the engine over and watch the spark plug for a nice deep blue spark. If my suspicions are correct, you'll have no spark at the spark plug indicating a faulty ignition coil. This doesn't necessarily mean the ignition coil is to blame (although highly likely) so you'll need to isolate the coil by way of removing the ground (kill) wire at the coil and again test for spark. However, here you may get a false indicator since you only have the problem when the engine is at operating temperature and by the time you tear the engine down to the point of exposing the coil, it will have cooled down to the point it may now have spark. One thing to bear in mind is that your engine may have a module called "Smart Spark". It is a device that advances the spark timing and they are found on select (but generally few) engines. This could be at fault, although I've yet to see one fail. Post back with your engines' ID numbers (model, specification and serial), they'll be found on the flywheel shroud.

 

Thanks for responding....
Here are the specs:
Family:SKH426U1G2RB
Model:CV15S
Spec.:41525
Disp:426cc
Ser:2532516894

Sears model No:917.256610

I'll try that spark plug trick on Monday. Hope you're right. I just want to get back to that slow cruise around the lawn....

 

If there's no spark, does that mean I should replace the whole ignition system or just the module?

 

Just the module. I've seen this many times. Most times it's a bad coil (Kohler calls it an ignition module). Sometimes it's the fuel pump. For some reason, some of them fail slowly. They seem to pump good when cool. The engine runs fine for a while, but the pump slowly loses volume, and after a while, the pump can't pump gas as fast as the engine consumes it. You can usually look at the fuel filter and see when this is happening. Usually the filter will be 1/4 to 3/4 full of gas when operating normally. When the pump begins to fail in this manner, the filter will gradually get empty, until it is completely empty, which is about when the engine starts to chug and die.

 

It's definitely not that. The fuel filter is always 3/4 full.

 

I'd be checking spark then, as Puey suggested.

For anyone who might happen to read this while trying to diagnose their mower...just because the fuel filter does empty doesn't mean the pump isn't working, but a sign that it could be the problem. A bad fuel line, clogged gas cap vent, or other things can also cause the problem.

 

Based on your model and spec numbers, you do not have the "Smart Spark" module. Therefore you needn't worry about this as a potential trouble spot, only the coil and kill system.

 

Hey,
So I installed a new ignition module and now it won't even turn over. I'm sure I screwed something up. I'm not the best with motors. I took off the blower housing, removed the old module, put on the new module, attatched wires, set the gap (I was told to do it with a buisness card) and went to start it and....not even a click. Any ideas?

 

Check the fuse near the starter solenoid. Maybe something shorted and blew the fuse while you had things taken apart. If so, look for pinched wires and other places a short may still be present.