LT40 power loss

[KWood255]

Good evening all,

I have a 2022 LT40 with the 38hp Kohler. This morning I started it to warm up before sawing. Within a few minutes of it idling, I heard the idle drop slightly, and began running a little rough. Upon engaging the blade the engine was slow to speed up, and lacked power. It appeared to be running on 1 cyl intermittently. 

I changed the air filter, fuel filter and spark plugs. No change. The mill's drive side cylinder's spark plug was wet with fuel, while the idle side's plug was black with carbon deposit nearly immediately. 

I swapped ignition coils presuming that was to blame. No change. I then swapped fuel injectors, no change again. 

I didn't realize the G38 has a diagnostic device until today. The codes came back at a faulty ignition coil, faulty crank sensor and a high voltage fault. 

Thinking a bad voltage regulator, I checked the terminals at idle and wide open. 14.8-14.9v consistent on my meter. Checking the diagnostic pages in the manual, all 3 above issues call for the ECU to be considered. I'm guessing the computer has fried, but no way to confirm yet. 

I will be calling WM Tech Support on Monday. Until then, any suggestions are sure welcomed and appreciated. Thanks. 

[TimW]

You might consider calling your engine manufacturer's tech support. 

[rusticretreater]

A bad crank sensor will affect the coils firing, so find a way to test it or just replace it.  

[Ben Cut-wright]

Good evening all,

I have a 2022 LT40 with the 38hp Kohler.

I changed the air filter, fuel filter and spark plugs. No change. The mill's drive side cylinder's spark plug was wet with fuel, while the idle side's plug was black with carbon deposit nearly immediately.

I swapped ignition coils presuming that was to blame. No change. I then swapped fuel injectors, no change again.

I didn't realize the G38 has a diagnostic device until today. The codes came back at a faulty ignition coil, faulty crank sensor and a high voltage fault.

Thinking a bad voltage regulator, I checked the terminals at idle and wide open. 14.8-14.9v consistent on my meter. Checking the diagnostic pages in the manual, all 3 above issues call for the ECU to be considered. I'm guessing the computer has fried, but no way to confirm yet.

I will be calling WM Tech Support on Monday. Until then, any suggestions are sure welcomed and appreciated. Thanks.

Trouble codes aren't as cut and dried as is commonly supposed. They indicate the area of concern but don't always condemn the component.

High and low circuit voltages can reek havoc on the solid state components.  How did you come by the "issues make the ECU suspect"?

There is most often a hierarchy in stored codes. First stored is usually diagnosed first. Not always so but is the norm. 

[KWood255]

Through a series of trail and error, the problem is narrowed down to the power supply to the drive side ignition coil. It is unclear yet if it's a broken/pinched wire, or something further up the chain. 

[Ben Cut-wright]

"power supply to the drive side ignition coil".

Don't know what you are calling the "drive side ignition coil"?

Does "series of trial and error" mean the "positive" terminal was tested and there was a fault in the voltage reading?   It might be interesting to know how the problem was narrowed down to that area.

[KWood255]

"power supply to the drive side ignition coil".

Don't know what you are calling the "drive side ignition coil"?

Does "series of trial and error" mean the "positive" terminal was tested and there was a fault in the voltage reading?  It might be interesting to know how the problem was narrowed down to that area.

The drive side of the mill...If looking at the engine from the operating side, would be the cylinder on the left (V twin). 

It's not totally solved yet but, but have measured resistance between the ignition coil power supply and the ECU. Tells me we have a broken wire somewhere along the line. Ohms reading of 3.5. I'm not great with electrical, but my understanding is it ohms reading should be sub 1.0. When I test other wiring areas on the mill, I'm getting readings of 0.4-0.5ohms. This again was 3.5. I cannot tell what that means exactly, aside from presumably it's a problem and need to further investigate. 

I have checked the majority of the harness in that area without seeing any obvious issues. A couple sharp bends in individual wires, but being braided I don't expect issues there. I'm  guessing the problem lies in or at a plug somewhere between the ignition and ECU. Yet to be confirmed 

[Ben Cut-wright]

The two ignition coils are wired and operate in the same manner.  If you check terminals of either they should test the same.  (EDIT: should read...testing each terminal should match the same terminal of the other coil.  NOT that all terminals should have the same test results) But...ohms testing is way down the list.  First test to see if signal or voltages lead you to question the *integrity of the wire or connectors. You should see the same test results at both coil leads.  But, you first need to know what test results to expect.


"measured resistance between the ignition coil power supply and the ECU"


The above means nothing without further explanation. Where did you place each probe when you tested. Were the wire-s *disconnected from ALL components?  You cannot compare test results with "other wiring areas on the mill" unless you know for sure the results should match.  The only circuit to get valid comparison is....the other coil. 

You swapped the coils, ran the engine, and the new "drive side plug"  was "wet" the other plug was " carbon black". That indicates the drive side was NOT getting spark and the other side was rich but firing.  The coils were swapped and there was No change. The next diagnostic step is testing coil power and control circuits. 

The tests are simple enough and will at least eliminate wiring and connections.  The coil that's firing is your roadmap in testing.