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John Deere 850 fuel knock and heavy black smoke out exhaust


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#16 Cvans OFFLINE  

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Posted April 26, 2021 - 11:25 PM

Thanks for updating us. Sounds like your making progress and hopefully tomorrow it will be back in full operation. If it appears plugged built a fire and throw the muffler in it and let it stay there until the fire burns out. If you can prop it upright while in the fire so it can draft it might help. Don't let it get hotter than a dull red or you will damage it. 


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#17 29 Chev ONLINE  

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Posted April 27, 2021 - 08:24 AM

Perhaps a piece of the exhaust inside the muffler has broken off inside and is floating around and at times restricting the passage of exhaust gasses - this may or may not show up with an inspection?  Have encountered a couple of exhaust restrictions as customers related their tales of strange things they have encountered.  First one was a double wall extension pipe on a car - the outside of the exhaust looked perfect but the layer inside had somehow collapsed and was restricting the exhaust gasses - exhaust was unusually quiet at the tail pipe.  Perhaps some raw fuel got into the exhaust system and then ignited causing a pipe deforming explosion.  Second was a new Y pipe on an 8 cyl pick up - customer picked up vehicle and complained of a definite lack of power.  Turned out that the pipe that the one half of the Y joined onto did not have a hole so only one bank was able to exhaust out the muffler and tail pipe.  Both these problems were not intermittent as your problem appears to be which makes me wonder if a piece of metal or something similar is "floating" around inside.    

 

just a thought.

 

Good luck with your pursuit - hope you find the problem and can at least recoup some of your time.


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#18 Mark 149 J. ONLINE  

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Posted April 27, 2021 - 09:22 AM

Sounds like you found the problem.  Great job!  I think replacing the muffler would eliminate the possibility of an comeback.  Cheap insurance for piece of mind.  If you get the time cut the muffler open to see what the problem was.  It would be interesting to see.


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#19 WNYTractorTinkerer OFFLINE  

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Posted April 27, 2021 - 09:47 AM

Perhaps a piece of the exhaust inside the muffler has broken off inside and is floating around and at times restricting the passage of exhaust gasses - this may or may not show up with an inspection?  Have encountered a couple of exhaust restrictions as customers related their tales of strange things they have encountered.  First one was a double wall extension pipe on a car - the outside of the exhaust looked perfect but the layer inside had somehow collapsed and was restricting the exhaust gasses - exhaust was unusually quiet at the tail pipe.  Perhaps some raw fuel got into the exhaust system and then ignited causing a pipe deforming explosion.  Second was a new Y pipe on an 8 cyl pick up - customer picked up vehicle and complained of a definite lack of power.  Turned out that the pipe that the one half of the Y joined onto did not have a hole so only one bank was able to exhaust out the muffler and tail pipe.  Both these problems were not intermittent as your problem appears to be which makes me wonder if a piece of metal or something similar is "floating" around inside.    

 

just a thought.

 

Good luck with your pursuit - hope you find the problem and can at least recoup some of your time.

Maybe someone shoved a bannana in the muffler!!   :smilewink:  :smilewink:  :smilewink:


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#20 29 Chev ONLINE  

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Posted April 27, 2021 - 11:44 AM

Maybe someone shoved a bannana in the muffler!!   :smilewink:  :smilewink:  :smilewink:

Could be a potato inside or other dense organic material that got put inside accidently or on purpose - might even be the remains of an old exhaust flapper valve that rusted away and fell down inside??  Would imagine a banana would break down fairly quickly from the heat but something much denser (like walnuts as an example) might not deteriorate very quickly since diesel fuel doesn't burn the same as gasoline and the majority of any flame is left in the combustion area - most of the spent combustion is soot and heat similar to an oil furnace.  Never seen a diesel tractor engine shoot any flame out of the exhaust the same way as a gasoline engine can.


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#21 diesel nut ONLINE  

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Posted April 28, 2021 - 11:50 AM

Never seen a diesel tractor engine shoot any flame out of the exhaust the same way as a gasoline engine can.

The flames that were coming out were right out of the open ports on the head and wouldn't be visible from the end of the muffler.  I'd say it was the last bit of burning fuel escaping just as the valve was opening.  I've run into that on quiet a few single and twin cylinder engines with separate intake and exhaust manifolds when the muffler was removed.

 

Yesterday I got the muffler unbolted from the manifold and the manifold bolted back on.  Fired right up and ran great.  The road  in front of the shop is on a fairly steep hill about 1/8 mile long so I took it down to the bottom and turned around and in 4th gear high range at full throttle it came up the hill nicely with no smoke, noise, and only the tiniest bit of power loss as it came up against the governor which would be the same as if there was a mower on it and I turned the pto on.  Pulled into the driveway and parked it out back of the shop where it ran perfect at full throttle for an hour until I shut it off so it wouldn't run out of fuel.

 

Got the intake manifold bolted back on and the air cleaner hooked back and going to take it outside and try it again.  Then just to make sure it is the muffler I plan on bolting it back on and see if it acts up again.  Need to borrow a tach that will read a piece of magnet stuck to the pto shaft to see what it's actually running at cause the one on the dash just barely goes up over 2000 and the adjustment for the top end speed on the linkage is at the max.  Want to see if it's actually running slow or the gauge on the tractor is reading low  


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#22 propane1 ONLINE  

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Posted April 28, 2021 - 02:46 PM

Well that’s great news.


Noel
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#23 KennyP ONLINE  

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Posted April 28, 2021 - 04:49 PM

Glad you are making headway on that!


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#24 diesel nut ONLINE  

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Posted April 28, 2021 - 10:40 PM

Success.  I put the complete intake back on including the air filter and it ran fine.  Let it cool down a bit so I could work on it and put the muffler back on.  Fired up and it was running great for about a minute then the engine started to slow down, smoke, knock, and the whistle was back.  Shut it off took the muffler back off and it ran great again, so I let it run another half hour or so before I shut it down and there was no issues.  Going to order a new muffler in the morning and when it gets here I can call the customer and tell him it's fixed and he can come get it. 

 

Thanks for the suggestions.  Stewart


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#25 diesel nut ONLINE  

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Posted May 06, 2021 - 08:59 PM

Well it's all done.  Got the new muffler in yesterday afternoon and put it on this morning.  Let it run at full speed for an hour then took it out on the road in front of the shop and it ran perfect.  Went to Harbor Freight the other day and picked up a photo tachometer to check the rpm on the pto shaft and according to the service manual it's turning at the required speed so I guess the tach on the dash is showing a bit slow.  Going to make the bill up in the morning and call the customer to come get it.

 

Here's a pic of the new muffler on the tractor

Resized_20210506_124836.jpeg

 


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#26 4getgto ONLINE  

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Posted May 07, 2021 - 04:39 AM

Glad you got it figured out. Hope you have some hair left 😉.
You had a kinda unique problem there that you don't hear much about.
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#27 diesel nut ONLINE  

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Posted May 07, 2021 - 12:06 PM

Glad you got it figured out. Hope you have some hair left .
You had a kinda unique problem there that you don't hear much about.

That's funny, I was talking with one of my friends last week about it before I figured out the problem and I had said I'm going to be completely bald from the stress of trying to fix it and what little hair might be left will be completely gray.

 

It's not a problem I've ever run into before.  Going to have to remember it in case I ever run into it again


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#28 Cvans OFFLINE  

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Posted May 07, 2021 - 08:24 PM

You ought to frame that picture and put it on your shop wall. 


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#29 29 Chev ONLINE  

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Posted May 08, 2021 - 11:24 AM

Glad you found the problem and got it fixed.  Sometimes diagnostics are a life lesson in patience and discovering the unresolved through a thought process.  Still remember the first intermittent condenser on a gas engine ignition system when I was about 20.  Only encountered three more during the 45 years since then - the first one took two plus days to figure out with the help of a timing light, thinking and head scratching with coworkers.  The next three - five minutes each.  Lessons like these tend to stick in ones mind I find.    


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