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Author Topic: Kohler 38 sputtering  (Read 637 times)

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Offline Stephen1

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Kohler 38 sputtering
« on: December 08, 2019, 02:38:31 PM »
I have a new gas Kohler 38 on the mill. when I activate the up/down I get an engine surge, when I activate the hydraulics I am now getting a cough and sputter, a small backfire today.
I changed the air filter, gas filter, I started  running HO gas this week, on the second tank. WM told me to raise the idle, made it worse, Bruno suggested loosening the gas cap, no difference, 
It runs great while sawing, the only thing I can think is something wrong with the alternator. 
Any ideas?
IDRY Vacum Kiln, LT40HDWide, BMS250 sharpener/setter 742b Bobcat, TCM forklift, Sthil 026,038, 461. 1952 TEA Fergusan Tractor

Offline doc henderson

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Re: Kohler 38 sputtering
« Reply #1 on: December 08, 2019, 03:36:07 PM »
could be a governor issue?  sounds like it happens when put under load.  i had trouble with the idle circuit on my log splitter.  a stihl mechanic knew off the start and knew how to get at it with a small wire to clean it out.  was surging as much of the fuel for running is supplied by the idle circuit and the extra is the high side circuit. 
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Offline Magicman

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Re: Kohler 38 sputtering
« Reply #2 on: December 08, 2019, 03:41:26 PM »
Your engine's alternator output/battery should read ~14.5 volts with the engine running at idle speed to handle the hydraulics.
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Offline Southside

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Re: Kohler 38 sputtering
« Reply #3 on: December 08, 2019, 05:19:06 PM »
Is that the EFI motor? There have been some issues with the throttle position sensor on those. 
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Offline beav

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Re: Kohler 38 sputtering
« Reply #4 on: December 08, 2019, 05:27:45 PM »
What magicman said. The system voltage is crashing upon using feed or hydraulics. Tighten alternate belt, check battery connections etc

Offline Cjross73

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Re: Kohler 38 sputtering
« Reply #5 on: December 08, 2019, 06:12:43 PM »
My old LT40 has done this and it's been a ground connection issue under the rail. 
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Offline Just Right

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Re: Kohler 38 sputtering
« Reply #6 on: December 08, 2019, 07:02:43 PM »
Did the new 38 come with a new carb or did you reuse the old one?
If you are enjoying what you are doing,  is it still work?

Offline Stephen1

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Re: Kohler 38 sputtering
« Reply #7 on: December 08, 2019, 07:07:45 PM »
SS yes its the new EFI motor, I called the dealer and I have to bring it in, 1 hr drive and he is back logged 2-3 weeks. I am hoping it is just a DIY problem.
Beav and MM , I will look into the belts and connections, its amazing what problems a loose belt or connection can cause, and get the tester out.
Thanks guys.
IDRY Vacum Kiln, LT40HDWide, BMS250 sharpener/setter 742b Bobcat, TCM forklift, Sthil 026,038, 461. 1952 TEA Fergusan Tractor

Offline jb616

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Re: Kohler 38 sputtering
« Reply #8 on: December 08, 2019, 08:07:41 PM »
@Stephen1 with EFI, are you maintaining fuel pressure?  I have not worked on this motor but most EFIs have a port that you can put a fuel pressure guage on and see if it is high enough. You will have to check specs to see what it is supposed to be and then get a reading on yours at idle and under load. As previously stated correct voltage is important on an EFI motor as well. Keep us posted as we can all learn.

Offline Stephen1

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Re: Kohler 38 sputtering
« Reply #9 on: December 08, 2019, 08:10:47 PM »
@Stephen1 with EFI, are you maintaining fuel pressure?  I have not worked on this motor but most EFIs have a port that you can put a fuel pressure guage on and see if it is high enough. You will have to check specs to see what it is supposed to be and then get a reading on yours at idle and under load. As previously stated correct voltage is important on an EFI motor as well. Keep us posted as we can all learn.
That is when we take to the dealer.  ;D
IDRY Vacum Kiln, LT40HDWide, BMS250 sharpener/setter 742b Bobcat, TCM forklift, Sthil 026,038, 461. 1952 TEA Fergusan Tractor

Offline Gere Flewelling

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Re: Kohler 38 sputtering
« Reply #10 on: December 08, 2019, 08:31:46 PM »
 I had a similar experience with a 26 hp Kohler on my mill. It would start to sputter when in a cut. It acted like it was skipping.  The check engine light would come on and I could get it to flash out a code.  I pulled spark plugs to find them black with soot. After replacing the spark plugs it would run fine for a tank or two of gas. Then it would return. Finally it got to the point that I could not get more than one cut before it would bother.  I found that once the check engine light came on, I could then shut the engine off and wait a few minutes and it would fire back up and run fine until it started working hard.  After much research I finally decided to replace the oxygen sensor.  The sensor was easy to change but hard to purchase. My local Kohler dealer had it on back order for more than a month. Out of desperation I reached out to Cook Saw (the mill manufacturer) to see if they could help. I had a new sensor in 3 days. Once installed the problem has gone away.  The first sensor finally arrived  from my local Kohler dealer. I decided to keep it for a spare if ever needed.  This was kind of a long explanation, but your symptoms sounded quite similar. I think if you turn your ignition switch on and off and back on again, it will start blinking out a trouble code. Count the number of fast blinks to determine the code number. This will give you a trouble code to discuss with your Kohler repair guy. Hopefully my experience will help get you back up and running again.
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Offline Ben Cut-wright

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Re: Kohler 38 sputtering
« Reply #11 on: December 09, 2019, 10:43:44 AM »
I have a new gas Kohler 38 on the mill. when I activate the up/down I get an engine surge, when I activate the hydraulics I am now getting a cough and sputter, a small backfire today.
I changed the air filter, gas filter, I started  running HO gas this week, on the second tank. WM told me to raise the idle, made it worse, Bruno suggested loosening the gas cap, no difference,
It runs great while sawing, the only thing I can think is something wrong with the alternator.
Any ideas?
Your initial description of the problem suggests there could be several possibilities.   (When an electrical load is activated) at engine idle seems to be when the engine falters.  That does NOT always dictate it is an engine management related fault, nor does it restrict cause to a faulty engine component.  Of course one could wrongly describe the alternator as an engine component.
 
The "engine runs great while sawing" eliminates most mechanical engine components.  Fuel quality and supply is greatest under load, so that might be eliminated.  Filters are more likely to show faults under engine load than at idle.  Pump gas, even of minimum octane and under 10% ethanol, should not cause running problems on the first tank of fuel. I would recommend using only top-tier non ethanol gasoline. 

"Raising the idle" is not well described and "made it worse" is speculative.    I find it helpful at specific and at limited times to manually throttle the engine to high RPM's when using the hydraulic pumps.  Under specific operating conditions electrical load on the alternator can exceed a small engine's ability to provide sufficient HP at idle.  Electrical loads operate off the highest source of voltage, which is the alternator if operating properly.  This creates a primary load on the alternator to provide energy.  It is easy and simple to test voltage at the time of fault, it may not be so easy to determine the cause of low voltage.  If voltage does not drop under the level the engine requirements dictate when the engine falters, then HP load has been surpassed. 

The alternator HP load should not be a constant cause of engine falter if all other factors are sound.  A drive belt that does not transmit HP will not load the engine as much as one that is loose. Charging voltage might decrease with a slack belt, but voltage must decrease below design limits of component requirements in order to create engine running problems.  Easy to test circuit voltage when fault occurs to better focus on electrical load or HP load. Batteries that do not have enough reserve can contribute to low circuit voltage.  Simple to dynamically load test a battery's state of charge and reserve by voltage test at engine off and hydraulic pump running. 

Alternator output will decrease when engine HP load is exceeded below design RPM's.  What must be determined is which comes first, loss of voltage or insufficient HP to drive the alternator.  A properly operating alternator, a fully charged battery, and a warmed up properly operating engine, should provide sufficient electrical energy to run the hydraulic pump, up down motor, or the forward-reverse motor without overloading an idling engine. 

Offline MartyParsons

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Re: Kohler 38 sputtering
« Reply #12 on: December 09, 2019, 08:53:01 PM »
Hello,

  Not seen any issues with the TPS ( throttle position sensor) on these 38 hp engines

  You can check the hi pressure fuel but only with a tool from Kohler.

  The 38 hp and the 26.5 Kohler engine uses the Delphi fuel pump

 

  You can check to see if there is any fuel at this port. If there is fuel here you need to replace the pump because the fuel needle is leaking.


 

    From the description and symptom described. I would guess it would be an electrical issue.

    Check the battery ( load test) Connections at the battery and fuses. Alternator belt tension.
   
    Ground at the engine.  ECU voltage should not drop below 7 volts and with the engine running it should be 13.8 to `14.2 volts.

    We have seen one 38 hp engine with a bad crimp at the starter ( would not start and no spark)

    One other engine had a bad ground at the engine and alternator. Caused engine surge and backfire. Check the wire connection crimp and paint removed under the connection.
  
    How many hours on the mill?

   The governor is mechanical and if the alternator was coming on at full charge it may make the engine stumble.

  Not sure if I am even close with this info but that is where I would start.

   Thanks Marty
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Offline Stephen1

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Re: Kohler 38 sputtering
« Reply #13 on: December 09, 2019, 09:01:57 PM »
Marty, there is only 290 hrs on the mill.
It was raining today and the mill is outside up at the yard so I did not make it to check out these ideas.
Tomorrow looks better and I will be able to check out the electrical
IDRY Vacum Kiln, LT40HDWide, BMS250 sharpener/setter 742b Bobcat, TCM forklift, Sthil 026,038, 461. 1952 TEA Fergusan Tractor

Offline esteadle

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Re: Kohler 38 sputtering
« Reply #14 on: December 10, 2019, 06:01:07 PM »
This sounds like a Command Pro EFI engine, and 38 hp would make it a ECH 980. 
Service Manuals for Kohler engines are available on Kohlerpower.com. 

Here's this engine: 
http://resources.kohler.com/power/kohler/enginesUS/pdf/62_690_13_EN.pdf

The section called EFI SYSTEM starting on P. 29 is worth a read-through. The system fuel pressure spec is 39 psi (but not sure what the injector pressure is... but I doubt that's your problem anyway). 

More than likely, the odd behavior you see is a bad sensor delivering bad input to the ECU and the ECU mis-computing the current demand and either over- or under-fueling the engine. Backfires mean too much fuel, or no spark allowing unburned fuel to pass out of the cylinders and into the exhaust manifold where it will certainly combust, and it goes "boom" as it does so. 


Quote (from above Service Manual): 
------------------
"During certain operating periods such as cold starts, warm up, acceleration, high load, etc., a richer air/fuel ratio is required and system operates in an open loop mode. In open loop operation oxygen sensor output is used to ensure engine is running rich, and controlling adjustments are based on primary sensor signals and programmed maps only. This system operates open loop whenever three conditions for closed loop operation are not being met"

The conditions are: 
● Oil temperature is greater than 50-60C (122-140F). 
● Oxygen sensor has warmed suffi ciently to provide a signal (minimum 400C, 752F). 
● Engine operation is at a steady state (not starting, warming up, accelerating, etc.).
------------------

Since your engine runs fine at steady state (while sawing) but has problems during burst load (hydraulics and up/down), I suspect you are running in Open Loop mode when the ECU wants to make the air/fuel ratio richer. That relies on the oxygen sensor to give it a good value. 

Oxygen sensors are peculiar devices, relying on special/expensive metals to measure how much oxygen is left after combustion (which should be pretty low). They get fouled up over time because they are constantly sitting in the engines dirty exhaust path, and the quality of fuel going into the combustion process can affect how quickly they get fouled. 

I learned this the hard way when I dumped the tiniest little bit of leftover chainsaw mix into the wife's Toyota. 3 dealer visits later, we figured out the check engine light was on because the Oxygen Sensor got fouled up from the mix oil that went through it. (You didn't do something silly like I did and run mix through the engine, right?)

In any case, if the oxygen sensor is fouled, the ECU would likely be told that the oxygen is low and the mixture needs to be leaned out (less fuel) so that a bit of oxygen is left over. So my guess is that is not your problem. 

Rather it could be that the Oxygen sensor is reading too much oxygen and the ECU is dumping in more fuel to get more combustion (and more power) and that causes your backfire (can't burn all that fuel fast enough). 

Kohler Service are good folks and if you call a dealer they will often troubleshoot it with you (especially if you tell them you have a sawmill and can't easily get the engine off and over to them). If you can get a tech to come out with their diagnostic software and a computer, they can probably solve the problem right then and there, because it reads the sensors and compares them to the "maps" that they expect to see. That usually fingers the bad sensor right then and there. 

Timber Harvester 30HT26 (setworks, hydraulic) Stihl 880 (36" bar).

Offline Stephen1

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Re: Kohler 38 sputtering
« Reply #15 on: December 10, 2019, 06:22:21 PM »
esteadle, I do not remember dumping any gas and oil mixin.  I have been know to dump old gas in the truck though. 
I was not able to make it to the saw today, My house sale firmed up last night and I have untill next friday to get moved...cold and snow here, so inside jobs, like packing are high on the list
IDRY Vacum Kiln, LT40HDWide, BMS250 sharpener/setter 742b Bobcat, TCM forklift, Sthil 026,038, 461. 1952 TEA Fergusan Tractor


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