Kohler 25HP Diode thingy on the coil?????

LD1 · Sep 7, 2012

I havent had a chance to look for a wiring diagram, but there is a diode or something that is burnt in two. (see picture)

This is on the plug that plugs into the coil. This is a 2-cylinder 25HP kohler motor. The plug has 3 slots. Red, White, and black wires. There are two wires together in each slot, I assume the second wires feed the other coil. This diode thing goes between the red and black.

Just wondering what in the heck it does and why it may have "popped". Cause I can start and run the mower and it runs fine. And no, it isnt just running on the other cylinder either. This cylinder is actually firing.

Thoughts??opinions???

Misfire · Sep 7, 2012

Might be the rectifier-regulator. Is the battery charging? Check the battery voltage with the engine running and without. It should be higher with the engine running.

Car Doc · Sep 7, 2012

Well I have a 23 hp v-twin Kohler and that part is under the shroud so I can tell you based on mine but i wonder if they just didn't get 12v for something else using the coil as a buss block and that was a fuse link? Does everything work like the amp gage and lites etc?

LD1 · Sep 7, 2012

Misfire said:
Might be the rectifier-regulator. Is the battery charging? Check the battery voltage with the engine running and without. It should be higher with the engine running.

I didnt have time to check bat voltage, and will be awhile before I get a chance. But that is one thing I was planning on doing.

Car Doc said:
Well I have a 23 hp v-twin Kohler and that part is under the shroud so I can tell you based on mine but i wonder if they just didn't get 12v for something else using the coil as a buss block and that was a fuse link? Does everything work like the amp gage and lites etc?

Yes, under a shroud. This is RIGHT on the plug that goes to the coil.

It is a zero-turn. So no lights. And no amp meter either. But the hour meter (the only accessory) does indeed work. I can hear it ticking as soon as the key is turned on.

Again, it will probabally be a week or so before I get a chance to take a look. But I will post an update if I figure anything out.

LD1 · Sep 8, 2012

Quick Update:

Definatally a diode. Heres the other side.

Got the following numbers/letters around the barrel

PK
IN6
277A
1.5KE
18A
0849

For whatever its worth???

And heres a diagram if you want. Page 38 I believe http://www.kohlerengines.com/onlinecatalog/pdf/sm_24_690_07.pdf

It dont show in the diagram. But it appears to just be a "clamping" diode. Used to dissipate the voltage spike cause when the coil fires. (I had to refer to the old college textbooks for that)

So now the delima. What to do?? There is a diode on the other side, and these are wired in parallel, so??? Wouldnt the one good diode still work in this circuit?? And since they arent even shown on the diagram, perhaps they dont use them anymore??? And if one ever failed, how would one even know cause everything still works fine??? The only way I found it was when the diode split in two, the two halves were still barly touching. Creating some smoke when key was on. But if something happened while mowing, and vibrated apart, one would never know. I really dont want to have to replace the whole engine harness which looks like the only good way short of trying to take the connectors appart to solder in a new diode and hope you dont break something. (connectors are a PITA.)

Additional thoughts? Opinions?

Edit, forgot to mention that this is a 27HP. Model CV740S

RandyT · Sep 8, 2012

Those are very much still in use. Except now that are between the wires on the electric pto clutch. The problem kohler was having with there spark advance modules was the electric clutch winding down to a stop was causing voltage spikes that were frying the ignition modules. This problem was also frying the ECU modules on the EFI engines,

Heard a story a few months ago concerning a Kohler EFI engine. The technician had his laptop connected to the diagnostics port for the engine. The engine and pto were running and when the guy shut off the pto, which didn't have a clamping diode installed fried the ECU on the engine and also fried his laptop.