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Old 08-24-2019, 12:45 PM   #1
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Kohler 6ekod low-speed shutdown

My relatively low-time (~400 hrs) Kohler 6EKOD genset has a persistent shutdown after about 45 minutes of operation. The data panel exhibits a low-speed shutdown error. After clearing the error code, the genset will restart, but fails again within minutes with the same error code. The manual states to "consult a Kohler professional" to diagnose this problem.

In an attempt to address the problem myself, and assuming the issue was fuel-related, I changed both the primary Racor and the on-engine secondary fuel filter elements. This genset has an electric fuel lift pump. There is a menu-driven "prime" function, which according to the manual, should fill the secondary filter and bleed the fuel system after a filter change. However, this function doesn't appear to work when the engine is hot (no "clicking" of the pump can be heard, no fuel out of the filter bleed valve can be seen). After manually filling the secondary filter, a an eventual restart occured, and the genset operated normally. Firmly patting myself on my back, I went back to boating as usual. 45 minutes later, same shutdown, same low-speed error code.

I'm baffled. Seems like an air leak would manifest itself well before 45 minutes, and careful inspection of the fuel system has not revealed a leak. All other operating parameters of the genset appear nominal (oil pressure, coolant temperature, output voltage, frequency, etc.) And yup, there is fuel in the tank!

Any ideas? May be time for the "Kohler professional" to step aboard?

Regards,

Pete
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Old 08-24-2019, 01:12 PM   #2
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I'm not familiar with a low speed error code on those. That usually shows up ad either a low voltage or low frequency error depending on the situation with then so-called ADC controller and governor.

Exactly what code is it displaying?

Right after start up, check the AC voltage output, and if you can the engine RPM and/or AC frequency. Wait 30-40min. Check the voltage and RPM and/or AC frequency again. A phototach is good for RPM, but a multimeter with frequency is easier since you may need to take a cover off for a phototach vs meter into outlet.

How did the voltage and/or RPM/AC-frequency change between initial and 30min tests, if at all?

How does the engine sound before shut-down? If the sound changes, and fuel is good, anither possibility is that air is getting sucked in on the suction side of the fuel system.

A 45min clean shutdown during smooth operation sounds to me most likely to be over temperature, e.g. clogged filter, thru hull or exchanger.
But, I'm just guessing.

With the code, I can probably guess better.

Cheers!
-Greg
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Old 08-24-2019, 03:38 PM   #3
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Hi Gkesden,

The only error code reported at the user level is my previously-stated "low speed shutdown". If there's another code behind that, I don't know how to access it.

All voltage and frequency (RPM) reported by the ADC controller are nominal, up until shutdown. And as-reported, so are oil pressure and coolant temp in the event log. As I said previously, everything appears nominal, until it isn't.

Engine shutdown is fairly rapid, but the engine RPM does degrade slowly over about a 20 second period, until the unit stops. Sounds every bit like fuel starvation to me. But darned if I can figure out why or how.

Thanks for your input. I'm tapped out for ideas, and will try and find a Kohler tech to look at the damn thing. Kinda sucks to have my genset down during summer!

Regards,

Pete
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Old 08-24-2019, 04:37 PM   #4
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Hi Pete,

I'm sorry. You have a different model than me. I missed the "K" in the model number. I don't know your model hands-on.

The service manual is here:
-- https://www.atlantismarine.co.uk/Ima...ile/tp6774.pdf

It says that the warning you are seeing is triggered by the AC voltage frequency. So, I'd start there and see if it is dropping or not. In other words, I'd check to see if there is a problem with the frequency or the measurement/trigger.

In "normal" circumstances", low frequency would be caused by the load being too high.

But, if the load isn't too high, then I guess the question is, why isn't the engine keeping up with the load. I'd first sanity check that things that shouldn't be wrong aren't wrong, e.g. the controller is set up for the right motor, etc.

Then, I'd treat the situation just the same as if it were an engine that weren't developing RPMs under throttle. How does the engine sound? Missing? How does the smoke look? What color and how much? If you open one injector at a time, can you confirm each fires? Is the governor doing its job and set correctly? Etc?

Sorry. I'm less good with this model other than looking at the service manual (which is admittedly a good start...but you can probably start there, too, without me transcribing it for you...but if you have questions, just lemme' know).
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Old 08-26-2019, 11:57 AM   #5
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Hi Gkesden,

Thanks for your suggestions and input. Much appreciated. And thanks for the link to the service manual. More info than the user's manual, particularly in the troubleshooting of the various sensors that can lead to a shut down.

The low speed shutdown error message is triggered by the AC voltage frequency, as you state. However, I believe that's because the software can measure this voltage internally, detect a reduction, and trigger the shutdown error code accordingly. But the REAL question is-why is that voltage degrading? And, equally obvious, it's probably degrading because something is causing the engine speed to slow. Given the software apparently cannot measure engine RPM directly, the error code is thus triggered by this AC voltage parameter.

If you happen to be watching the ADC display during the few seconds prior to shutdown, sure enough, the AC voltage declines as the engine labors and slows. However, when the genset is at full load (and not overloaded) and operating properly, all operating parameters that the display provides (AC voltage and frequency, coolant temp, oil pressure, etc.) are nominal. And if one of the other sensors that can shut down the genset (coolant temp, oil pres, etc.) is, in fact causing the low-speed shutdown, why isn't the ADC reporting THAT fault, vice "low speed shutdown"???? And the event log lacks resolution, and simply reports the error code at last event, vice other parameters DURING the last event. Thus, it's of little use.

As you state, why isn't the engine keeping up with the load? The ADC is set for the correct motor, operating speed, AC voltage and phase, etc. It does not smoke, miss, or otherwise exhibit signs of distress when operating as it should. I haven't cracked an injector under load to detect if all are operating. Given the lack of smoke and smooth operation when running, believe that's a non-issue. And given the governor is not mechanically controlled, believe checking for THAT thing to be in-spec is out of my wheelhouse.

My next step will be somewhat of a shot in the dark, but I'm going to open the coolant pump and verify that the impeller is intact, and I'm not really seeing a coolant issue shutdown that, for some unexplained software fault isn't allowing the ADC to report THAT error code, vice the low-speed shutdown.

And continue my hunt for an actual Kohler tech to look at this thing. Hard to do this time of the year.

Regards,

Pete
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Old 08-27-2019, 02:07 AM   #6
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Hey Pete,

Let me ask you a few more questions and then offer some more wild speculation based upon what I know already (maybe more wild speculation after I get more bits from you).

1) When you write that the "engine labors and slows", what are the signs of it "laboring" other than slowing? Your description denies a bunch of the common ones.

2) What is the load on the system at the time of failure? Will it run longer at a much lower load? What about if disconnected from any load? Less time under a really heavy max load?

3) Have you checked the frequency or RPMs yourself?

4) As the frequency is reported to be dropped, can you hear the engine slowing?

5) The system /is/ mechanically governed. If you look at the governor (see page 25 of the service manual), what position is that arm in? In particular is it fully opening the throttle, or close to it? Do you see any obstructions, damage, mending, etc in the mechanical linkage between the governor and throttle arm?

Now, wild speculation, e.g. "It could be...."

1) The controller board. Perhaps, for example, it is mismeasuring frequency once it warms up. You can rule this out 100% for free in seconds. Just check the RPM or AC frequency as the failure approaches You can check the frequency on the controller or at any outlet on the genset (vs inverter or shore power). Or, you can check the RPM of the engine with the same phototach you use for your main engine(s). According to page 25 you should find, "59-63 Hz (1800 rpm under full load and 1890 rpm under no load)." If reality isn't matching what the controller is reporting, check again using a different instrument or method, but if the frequency/RPM is good and the controller is reporting otherwise, you found your (very unlikely) problem. Replace the board.

2) A fuel supply obstruction outside the motor, e.g. bad fuel, logged line, bad fuel shut-off valve, bad hose, bad filter, etc. I'm betting against this because the generator starts and runs fine, and shuts down with only a drop-off, and without smoking, running rough, or especially RPM surging.

3) Fuel supply obstruction on the motor. For example, the onboard fuel filter.

4) Fuel return problem, e.g. closed return valve. The back pressure could cause a failure that bleeds off over time and lets things work again. But, I bet against this, because you report no smoke or other problems.

5) The fuel solenoid, or the connections or wiring to it. They could, for example, be vibrating loose or coming apart at a connection, or corroded and high resistance, or something. This could choke fuel.

6) The electric lifter pump on the motor. It could be bad, clogged, or have bad connections or wiring. This could choke fuel.

7) The governor. The motor /is/ mechanically governed. There is no smarts to it. If the motor slows down, it should advance the throttle arm. If that throttle arm isn't advancing, or advancing enough, there is likely a problem. Also, something could be bent, changing the angles, causing the advance not to be enough. See how RPMs respond to load to see if this seems to be working. Also, make sure it is pushing the throttle open when RPMs go down. It is mechanical -- you can see it move. See page 25 of the service manual for a picture.

There are normally six things that lead one to believe RPMs are coming down in mechanically governed systems like this: failed instrumentation/alarms (bad board, wiring connection etc), fuel supply, fuel return, high-pressure injection, governing and load. All of these but instrumentation/alarms, governing, and load should result in some problem with the way the motor runs, e.g. white smoke. And, even load will often black smoke.

This is just me thinking through it as if I was trying to debug it.

Cheers!
-Greg
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Old 08-27-2019, 02:49 AM   #7
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Hey Pete,

It would be hard to imagine a failure mode where a cooling or raw water flow caused that error code, I think.
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Old 08-27-2019, 11:01 AM   #8
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Hi Greg,

Many thanks for your thoughtful inputs. Much obliged, and much appreciated.

Some progress: I was able to get a "Kohler Whisperer" aboard from Tacoma Diesel yesterday. Fortunately, I was able to demonstrate the shutdown to him, and he launched into a professional look into the situation.

Bottom line, after about one hour of investigation, the issue was operator error (mine) upon replacement of the fuel filters. Somewhere in the fuel system, post-secondary filter, was an air lock. And, despite my best efforts to bleed the fuel system after replacing both the primary and secondary filters, that air lock persisted.

His recommendation on how to properly bleed the fuel system after a filter change is to:
a. Verify there is fuel flow to, and through the primary filter after it's replaced. In my case, that was done properly, as there is positive head to the Racor, and the filter was observed to fill by gravity after the new filter element was replaced.
b. Crack the bleed valve on the secondary filter.
c. Clear the low-speed error code on the ADC.
d. Perform the "prime" function via the ADC (several times, as needed) until clear fuel flows from the bleed valve.
e. Close the bleed valve, start and run.

Elementary, my dear Watson. Although it did take multiple tries before this was ultimately successful.

In my defense, this process is different from that shown in the User's Manual. In the Manual, bleeding the secondary filter makes no mention of the bleed valve. It simply states after replacing the secondary filter to run the prime function, and restart the engine. Apparently, doing so without cracking the bleed valve pushes the air in the filter downstream toward the injection pump, where it hangs around and continues to fuel-starve the engine.

During my filter change process, I did ponder where the air in the secondary filter actually went during the prime function. But as this is my first electronically-controlled genset (I'm a 20-year vet on Northern Lights mechanical stuff with mechanical lift pumps, for instance), I figured the wizards that designed this Kohler in this enlightened age must have figured out how to displace the air with fresh fuel without opening the bleed valve, and proceeded as-directed in the manual. Uhhh, not so much. They simply omitted the "open the bleed valve" step in the manual. Thus on my first attempt at a restart, the airlock developed, and I was stumped. That slug of air takes a loooonnnnggg time to work it's way out of the fuel system, if you follow the factory instructions on a filter change explicitly.

In Kohler's defense, the manual does discuss further air bleed procedures, involving the bleed valve. But IMHO, once the damage is done, and air is introduced downstream of the secondary filter, you're screwed. It's REAL hard to get out from there.

Lesson learned for me. Manual's ain't always accurate. And a diesel engine's a diesel engine, electronically controlled or not. Keep the air out-they run fine. And all my blather regarding other issues leading to a low-speed shutdown error code were a result of my over-thinking this new-to-me modern-age electronically controlled genset.

Sigh. Thanks again.

Regards,

Pete
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Old 08-27-2019, 05:23 PM   #9
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Hey Pete,

Good work in finding the person who could fix it!

I am still puzzled as to how the air kept being a problem after hours of operation. Normally air will stop the engine or cause it to stutter. But, after a little bit, if the engine keeps going, it manages to move the air out. I'd really have thought that after a few 45 minute episodes, hours of operation, the air would be gone.

It makes me wonder if there is a leak on the suction side and it is pulling more air in. But, if the problem was fixed by full bleed, I guess not.

Regardless, good work! And, now time for actual boating!
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Old 08-27-2019, 05:34 PM   #10
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I probably should also say +2 to the crowd who usually jumps into things like this and says "Nearly 100% of the time problem X appears right after routine maintenance Y, the problem was cause my Y" and to examine every detail of it.

Occam's Razor wins again!
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Old 08-27-2019, 05:52 PM   #11
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Hi Greg,

My puzzlement also! How can an engine run, apparently faultlessly, for 45 minutes, and then shutdown with an apparent fuel starvation issue without there being an air leak somewhere upstream of the injection pump? And now, despite finding no evidence of such a leak, and after being well and truly bled, it runs just fine, at least for 2+hours. Maybe the moon is now aligned with Venus, that sunspot error has dissipated, and all is well.

Off for the weekend, and I'll run the crap out of the thing. And hopefully won't have anything further to report!

Ockham's Razor for sure!

Thanks again, to all.

Regards,

Pete
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Old 08-27-2019, 05:56 PM   #12
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Hey Pete,

My wild guess, and it is only a wild guess, is that there was a suction side leak that got tightened up when the mechanic was checking on things. Or, maybe an obstruction that was causing the leak that got cleared, relieving the suction causing the leak.

But, I'm just wild guessing. The fact picture seems odd to me. But, that, I guess, is the difference between me and a full-time professional -- they've seen it all!
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