Go Bottom790 engine help
 | Neven Mikic
Join Date: Posts: 1 
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2000-12-21 22688
I would appreciate any help before going to the dealer in regards to my new 790 with 12 hours on it.About 3 days ago I was using it to clear some snow and no problems, I did notice a couple of sparks come out of the exhaust pipe.Well today I was moving about 2 inches of fresh snow and running it at about 1500rpm and after a half hour the motor began to smoke and i lost power.The motor seemed to knock more.After shutting it off and checking air filter, oil and fuel filter it was all ok.The fuel is the same I used a fw nights ago and it was almost full.The temperture outside was 8 degrees and I don't think that would make a diffrence.I started it up again to drive to garage and it started ok but still I had loss of power and smoke.No drips anywhere.Any suggestions?Thanks NEVEN
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| Bird Senter
Join Date: Jun 1999 Posts: 962 
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2000-12-21 22695
Did you try opening the throttle on up to blow the soot out of it? I don't know, but wonder if the engine isn't building too much carbon only running at 1500 rpm. ....
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| mark
Join Date: Feb 2002 Posts: 188 Virginia
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2000-12-21 22700
Nevin, Sorry to hear of your recent experience. I am know expert by any means but was wondering was your tractor stored inside or out? What are the chances of debris (mouse nest etc.) having found it's way into the intake or down the exhaust pipe on the motor? When you mentioned seeing sparks out the exhaust that to me suggests foreign matter in the muffler. From the sounds of things I don't believe I would start the engine/move the tractor until I determined what your problem is. I am sure this goes without saying, but if there is any internal damage to the motor you don't want to make things worse for yourself by starting and running the engine again. Good Luck with the troubleshooting and please update the list as to your final resolution/findings. Regards and Merry Christmas... Mark ....
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| Neven Mikic
Join Date: Posts: 1
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2000-12-21 22704
Thanks for the help especially about the rpm being too low because I thought about that too.The tractor is garaged and as for the sparks, it maybe due to the factory option a very short pipe about 3 inches coming out from the engine instead of the usual pipe stack going upwards that the 790's have.I started it up this afternoon about 10 degrees and it acted almost normal it still had a little power shortage but the smoke was gone and the loud knock was gone. ....
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| dave piper
Join Date: Posts: 1
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2000-12-21 22706
That sounds like a fuel geling {jelling} problem. Are you using any cold weather additives in the fuel? ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2000-12-22 22712
Diesels will build up carbon in the exhaust system when operated for prolonged periods at low rpm. Sparks from the exhaust may simply be ignited loose carbon particles. Diesels do like to be worked so they get up to full operating temperatures for prolonged periods.
If the smoke is very black, then a restricted air intake might be suspected. However, dark gray smoke plus the rest of your description sounds like fuel starvation. Fuel starvation can result from a number of problems. Fuel gelling, mentioned by Dave, is a good guess.
If fuel gelling is the problem, you probably should arm yourself with several new fuel filters. Gelling is caused by the formation of wax particles in the fuel at cold temperatures. In mild cases of gelling, the fuel still flows, but wax particles slowly clog the fuel filter. Basically, it doesn't get much better. Neither fuel additives nor warmer temperatures do much about wax particles already formed. The filters can't be salvaged and must be replaced. However, it would be good to add an anti-gel additive if you haven't done so already. There's a chance that fuel in the tank stayed warmer than fuel in the filter bowl, and it may not have gelled. The solution then is a relatively simple flushing of the lines and replacement of the filter. Otherwise, draining and flushing of the tank may be required as well. If fuel in the tank appears clear, then it's probably OK. The 'cloud-point' is the temperature at which wax starts forming in the fuel. Cloud points for some winter blend #2 fuel in some regions is as high as 15F at which point, the fuel will appear cloudy.
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| Neven Mikic
Join Date: Posts: 1
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2000-12-22 22715
I'll give the fuel additive a try.Thanks for the information. ....
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 | Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York
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2000-12-22 22718
Nevin the ideas that have been brought up are right on. I first would add a good anti-gel additive and then replace the fuel filters. The sparks are normal ocasionally but if they are there continually I would have it looked into. For what your discription of what happened it is a classic case if winter fuel iceing. You did not say as to wheather your storage was heated or not and I can only assume it isn't. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2000-12-23 22732
Just a couple of comments if you're new to tractors. First is that diesels don't warm up much at low idle speeds. 1500-RPM is a common idle speed for warming up a diesel. It's also common to give a diesel a cool down period, especially after a hard run, at around 800-RPM. Second is that replacing fuel filters requires bleeding the fuel lines. Air in the lines is another source of fuel starvation and would cause virtually the same symptoms as fuel gelling. Most owners’ manuals give instructions for bleeding the lines. However, the injector pump on my Ford is very particular, and the manual procedure often doesn't work the first time. ....
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| Rob Munach
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2000-12-23 22736
I thought the pumps on the 790 were self bleeding. ....
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| Neven Mikic
Join Date: Posts: 1
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2000-12-23 22748
The 790's are self bleeding and after changing the filter and adding the anti gel additive it ran just fine.I'm sure the 28degree temperture also helped. ....
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