Kohler CH740s .. what the fu_k is it with these Kohler (Phelon) Ignition Coils ??

[OzPete]

So, chasing some seriosly in-depth Kohler Tech info here Gentlemen ...
I have here an 2008 build Kohler Command V-Twin, Model CH740S-0095. Serial No.3724211771.
WHAT PART NUMBER DO I USE TO ORDER TO REPLACE BOTH THE IGNITION COILS ???
So "Why", you may ask.
Long story short ... A new to me (& frustrated) client brought it in and asked me to fit the 25 707 03-S Ignition Module kit that he had in his hand.
He had ordered 2 new ignition coils over the phone from his usual Kohler Dealer. Apparently someone had decided that it needed one or both new coils due to loss of spark after 20 - 30mins of running. Jeezuz I hate other dudes diagnoses !
Anyway, so the instruction sheet that came with the the seemed to indicate that it was correct for a CH740 engine.
Well yes, it fitted. But it didn't work.
NOTE: The engine ran perfectly with the original coils .. absolutely perfectly. Just not all day. Coz yep, as suggested, after 20 odd minutes one coil failed, and she don't run no good no more !!
So with the (I dunno, upgraded, modified, different), two new coils from the 25 707 03-S Ignition Module Kit, she runs even worse.
+++++++++++++++++++++++++++++++++++++++++++++++
Please Note: I only want to know about IN DEPTH Ignition System info for these engines !!!
Please don't go on about all aother engine functions, as they've all been checked & confirmed. The engine and it's fuel system etc is ALL
in EXCELLENT condition.
Thanks Fellas.
Pete

 

[StarTech]

When I look up the CH740-0095 and there are two coils depending on if it had the MDI conversion or not. But yes Kohler indicates the 25 707 03-S MDI conversion kit is the correct kit. You have to make sure you don't apply 12VDC to the new coils.

And it possible that one coil damaged the other originally. I have had steering diodes to fail in them before here. So diagnostic was probably right.

Now with the new kit you may have a defective ignition coil which is possible. There no test procedure other than swapping them out with new coils as it is impossible for us to test these in the field. They are considered plug and play items.

 

[OzPete]

Hello StarTech, and thanks for your reply.

First up, I am a 70 year old former Kohler Dealership Owner and Service Manager. But I’ve been retired now for over 15 years. So whilst I was VERY familiar with the Kohler Command singles and V-Twins back in the early to mid 2000's, I've been out of the industry now since 2007.
This engine still had the (presumably original) DSI ignition, the coils having the 3-terminal connectors and the 12 volt supply.
Note: All of the following was of course being done with the blower housing removed for access, but in short runs due to limited cooling….

Having fitted the new coils from the 25 707 03-S MDI Module Conversion Kit the engine will start & run, but basically only running on one cylinder. No.1 cylinder running normally, whilst No.2 cylinder behaving as though the timing is a mile out. First thing we did was confirm that the flywheel key was NOT sheared. Then we thought “OK, one of the new coils is faulty”. A reasonably logical assumption.
So we swapped the coils over, expecting to see the problem move from Cylinder 2 to Cylinder 1.
But NO. …Cylinder number 2 was still the problem. With the white ‘kill wire’ removed, we then isolated each coil separately by shorting the kill wire terminals to ground .. shorting Cyl 2’s coil made very little difference to how the engine ran, (because Cyl 1’s coil was working fine so the engine ran on just Cyl 1.) But when we shorted Cyl 1 the engine basically spluttered to a stop.
At this point we put the original 3-wire DSI coils back on and she runs like a dream, with almost identical exhaust temperatures, and if we short the DSI coils individually the RPM drop is the same both sides.
…..
Is it possible that the new MDI coils should be used with a different flywheel ?

 

[StarTech]

It seems I remember there was a time where number 2 had to be flipped upside down on some Kohler twins but that may be something I read several years ago so don't assume I remember things correctly. But it is worth a try.

As for the flywheel it shouldn't be a problem as there is only one trigger magnet set for both coils. If the engine runs fine on one coil and not the other it is something to with the coil mounting place.

I simply don't work on enough Kohler engines to be consider anywhere near an expert.

This from the service manual has always confused me maybe someone else can make sense of it.

 

[ILENGINE]

It seems I remember there was a time where number 2 had to be flipped upside down on some Kohler twins but that may be something I read several years ago so don't assume I remember things correctly. But it is worth a try.

As for the flywheel it shouldn't be a problem as there is only one trigger magnet set for both coils. If the engine runs fine on one coil and not the other it is something to with the coil mounting place.

I simply don't work on enough Kohler engines to be consider anywhere near an expert.

This from the service manual has always confused me maybe someone else can make sense of it.

View attachment 65150

Some of the fixed timing engines do require that one of the modules be installed upside down from the other. I think it was number 2 that goes upside down.