Why does a gas engine keep running after shut off?

[YellowHammer]

Get a compression tester or borrow one at your local Autozone and check your cylinders.  That will tell you if there is damage.

Get a spark plug or ignition tester and the next time it starts dieseling, see if it's getting a spark.  Or, pull the plug wires off and see if that changes anything.  Obviously, with no spark and the engine keeps running, then the ignition isn't the problem, and you don' need an ignition kill switch.   

I also agree, if there is not a full line shutoff, install one.  They are cheap. 

[Ben Cut-wright]

"Kill switch" you added proved the circuit involved was the reason the engine wouldn't shut off properly.  These engines can have one of three types of ignition systems.  They all use (short to ground) to kill the engine.  Because the switch you installed does that very thing, it is apparent the woodmizer switch-circuit isn't providing ground to the ignition kill when the switch is turned off. 

Could be the woodmizer switch is bad or...
the switch they used on your mill has NO provision to ground the ignition, or
Could be a smart ignition has wires connected to the wrong terminals.

Diodes, often used in a (single kill wire-multiple coils scheme,  can be faulty and cause a "can't kill the engine" symptom. 
   


I understand that isn't what happened, but WoodMizer should not be "encouraging YOU to find a fix".  That is their responsibility and duty to their customers.


The prior notice of "watery" oil, subsequent installation of a kill switch, and "the next day" the engine quit,  are the clues you use to "expect a leaky diaphragm in the fuel pump"??  Easy enough to test fuel flow and check for high oil level in the crankcase.  Best to actually do testing and use those results than try to prove expectations.


Shutting the fuel line off when not in use is good practice. It won't prevent gas getting into the crankcase (if that is what has happened) if the engine is/will run with a busted fuel pump diaphragm.

If the engine oil is suspect in any way, change it and the filter immediately.

[beenthere]

My Kawasaki Deere engines have a fuel shut-off solenoid (as I understand) that shuts off the fuel moments before the engine is killed. That burns up the un-burned fuel and won't let it backfire or "diesel". 

[TBrown99]

Thanks for the great feedback!

Pulling one of the spark plug caps did shut down the engine.

I suspected the fuel pump only because WoodMizer recommended checking it. On disconnecting the fuel pump and lowering it below the gas tank, I found considerable leakage from within the housing near the pump. The video "Kohler ch740 27hp v-twin leaky fuel pump gas getting into engine fix" shows how the pump diaphragm can tear... If this truly happens often, this would seem to be a truly horrible engine design.

The new pump is supposed to arrive today.

Why should this engine have a spare white wire with an open end available to easily add a kill circuit? which WoodMizer recommended I use.

A friend has some testing equipment so we'll do this part.

The big lesson for me is to check the dipstick (look and smell) before each use.

Other information above will be addressed shortly. 
 

[Magicman]

A leaking fuel pump diaphragm will allow fuel to enter the crankcase on any engine.  I have had to replace the lift pump twice over the years on my old 1530 John Deere e/w a Diesel engine.  Stuff happens.

[barbender]

 A faulty fuel pump could cause gas in your oil, but it has nothing to do with your engine not wanting to shut off. 

[Magicman]

True, I was responding to TBrown99's Reply #21 and Jeff's Reply #22 above.

[TBrown99]

Determined that I need to upgrade the valve train before I can complete fuel pump install. Shipping isn't as fast for this item so update will be delayed. (Pump install instructions so stated this upgrade requirement.)

[barbender]

My reply wasn't directed at you, Magic😊

[rusticretreater]

Determined that I need to upgrade the valve train before I can complete fuel pump install.(Pump install instructions so stated this upgrade requirement.)

Never heard that one before.  What is the nature of the upgrade?  Maybe send a stronger pulse to a heavier duty pump?

The extra white wire available for a kill switch is what that is for, an emergency kill switch.  This engine is used for a variety of vehicles, machines.  Some may have need for an emergency stop.

[TBrown99]

The instructions don't mention the issue with original design.

See clipped text here on valve train switch taken from the pump install instructions.

I'm comfortable doing this because I'm generally good at mechanics however I don't have a lot of experience so I'm slightly apprehensive. I'm hoping the instructions indicate whether I need to replace the rods as they are included in the package. If so, I hope that those simply screw out and don't require further disassembly...

When putting this back together, I will try to fill the gas line with gas before attaching it... not knowing if the pump will be able to handle an empty line... thinking that "priming" might be necessary. Figure it can't hurt to help fill the line... simply by holding it low for a second to fill via gravity...

[Al_Smith]

Often times auto ignition is caused by carboned up pistons and cylinder heads .There are about a zillion ways to remove it ,One is  to inject water mist into a running engine and that method was used on model D John Deere tractors that could run on well head crude oil in some cases .You can buy combustion chamber cleaners also .
It's like the carb for some reason is allowing a super rich fuel mix but often is spuartic when it will do it .Fact I've got a 23 HP Kawasaki on a Toro zero turn that periodically  I need to disect and rod out the passages .It will bing,bang,hiccup and fart then clear up and run okay only to do all over again in 15 minutes some times.Drives me bonkers but it never "runs on ".

[Al_Smith]

The crux of the problem as per EPA mandates is the use of non ajustable carbs .Why they make such a big deal of small engines remains a mystery to me,like they pollute as if they were a huge ocean going tanker ship .Making mountains out of mole hills . No matter now we have to deal with them .

[Ben Cut-wright]

Tried to reply yesterday but could not log on. Your engine may already be equipped with the correct design rocker arm.

The rocker arm; bolt, and trunnion, are easily removed and replaced.  What you should know is that this engine uses hydraulic lifters. It's good practice to be sure the lifter has relieved before cranking the engine.  The instructions may or may not include the procedure. 

Are the "rods" the push rods? If so, it is good practice to slightly rotate the old rods (prior to and at the instance of) lifting them out of the engine. 

The rocker cover fuel pump has sufficient ability to preform in a nearly 3' suction head. 
 
Back to the "Shutoff" problem.  You say the engine stopped running by, " Pulling one of the spark plug caps did shut down the engine."  That's interesting.  The next step in diagnosis would be to determine which type of "smart spark ignition system" you have.  The wiring diagrams show  the "white kill" wire on ALL types but obviously it was never needed to kill your engine.  The problem began, as I understand it, long after you owned the unit and it had shut down properly until....it didn't.  

On some engine installations the ignition switch supplies battery voltage to the smart ignition module.  It ?might be that removing the battery supply is one method (the one WoodMizer uses) of killing the engine.  If the module became faulty, (say a bad diode) then the engine ?might continue running even though the ignition switch wasn't supplying power to the module.  Then, similar to the simple CD coil ignition, the engine will die by removing the spark from the coil-coils still producing current. 

The smart ignition systems employ "electronic spark advance", a really beneficial feature on engines designed to provide power at many different RPM's.  There are many video and text instructions on fitting the fixed spark coils to replace the problematic, expensive, and harder to diagnose, "smart" systems.  Since the engine you have is probably fitted with one of the smart systems, I would suggest diagnosis and repair of what you have.  The benefit for you is  cranking to start with less spark advance.  Somewhat less load on the starter and most engines prefer less spark advance to start. All ignition types for these engines restrict full RPM advance at the most beneficial for the particular engine. 

[TBrown99]

That's a lot to digest. 

Thanks for the tip on "rods"... Will take special note there. Noticing the manual has a lot on the hydraulic lifters. 

Seems like I may need to find a local mechanic. 

The mill itself and now the engine seem to often have issues to deal with. Too many, IMHO.  

[TBrown99]

I made an error in thinking I have to replace the valve train part... My machine has a later setup... So, I will proceed tomorrow with install... Fortunately, a friend with a bit more experience reviewed the situation with me and we compared serial numbers which shows we don't quality as "before"... but are well after... Yah!

[TBrown99]

The fuel pump replacement was straightforward... Done! This resolved the problem of the engine cutting out.

I took apart the old diaphragm and didn't see an obvious crack that might let gas through.

The other problem with the engine not shutting off was also resolved with this fix. After the engine warmed up, it now shuts down normally. So, it looks like the pump problem caused the shutdown problem. No? Any idea why?

[Ben Cut-wright]

Good to hear those issues were resolved.

Is your logic that a failing fuel pump 'prevented the engine from shutting down properly'...and a new fuel pump 'restored proper ignition key shutdown'??

[TBrown99]

I passed the connection between the two problems by WoodMizer's engine specialist and he said for sure... gas in the oil can do this. I didn't get the whole explanation. Anyway. He said the fuel pump issue is common and I should just move on, don't try to do testing... Keep closer eye on the oil, daily checking...

[YellowHammer]

Engines are designed to lubricate with oil and burn fuel, not the other way around. 

Is it under warranty?  If so, I would 100% do a compression test and compare to specs and if it is low, start a warranty claim.  If not, well I would still do it to know the health of my engines, and if there was any damage.

Either way, I would also change the oil once again, just to make sure the contamination has been purged as well as smell it to see if these is any gas in it.  

[TBrown99]

Yes, my friend will stop over to do the compression test... The machine is 4 years now so we're on our own. But asking for a new engine was my first thought. A failure like this after only 530 hours seems ridiculous.

I'll wait an hour or two of operating time to change oil and filter. And I will check the dipstick each time I start up for the day.

I believe I have the same exact fuel pump problem on my CH980 Wallenstein chipper  (35 hp).  Incredible.

Search Google for "fuel pumps on these kohler engines going bad and filling the crankcase" and it's clear that this is a widespread issue. Maybe WoodMizer could have contacted owners on this fact. They will say that the manual recommends checking the oil daily so it's on owners to catch the problem early to minimize possible damage.  Very questionable! 

[Ben Cut-wright]

Most certainly true, that particular type of fuel pump can go bad.  There may be as many YouTube videos with instructions for replacing the valve cover mechanical pump with a pulse type pump.  Would that ensure prevention of gas getting into the oil?  Depends.

It would be very beneficial to learn from your situation "Why a failing fuel pump would prevent normal shutdown of that engine?". 

The owners' manual isn't trying to limit liability by instructing to check the oil.  If daily sniffing of the dipstick is the determinate for gas contamination, there is good chance the engine has already been damaged.   

[jpassardi]

Some gas dilution of the oil won't necessarily cause bearing or camshaft damage. How much did the oil level increase? That will give you a rough dilution estimate. Obviously, the other factor is how long it was run while diluted.
Change the oil and send it. The damage if any is already done -unless you plan to rebuild it.

[TBrown99]

There was about an extra 1/5th volume of the oil & gas mix. 

I expect it was for an extended period. I found both my chipper kohler and pressure washer kohler also have the same problem. I guess they're made for it.

I'm moving on. Seems to be running fine. Did a big 25" wide maple today without any signs of issues. 

Did change the oil again today with a new filter. 

[LogPup]

It is good insurance to pre-trip it every time you use it.  Can head off some costly break downs.  I had a truck that was running fine.  Got up the next morning and did my pre-trip and the oil was milky.  If I had gone on down the road that day I probably would have ended up dropping the engine.