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Discussion Starter · #1 ·
I recently bought a 455 and it runs great.....once it gets past the hunting. The engine hunts on cold starting. It will do this for about 20 seconds and then smooths out and runs fine. It will also not respond to the throttle when it is hunting. Once it is warm you can turn it off and restart it without hunting. This has no other effect on the tractor running at all as it runs great and doesn't smoke but the hunting is really annoying. I have replace the fuel sending unit, all the rubber fuel lines, cleaned the tank and tested the fuel pump according to the manual and it checks out fine. It seems like I have a fuel delivery issue or air leak in the fuel line that I can't find. Any suggestions?
 

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Discussion Starter · #3 ·
It will actually hunt to the point that it will die once in a while. Ignore the excess clatter as none of the fender pan is bolted back down.

 

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Nope, that's not normal. I can't see the video - says it's private.

Where do you have the throttle set when you're starting it? Also, you did not mention it, but be sure to check the air and fuel filters. The fuel shutoff at the fuel filter is notorious for breaking when you try to actually use it, so don't bother - only a few drops of fuel will come out anyway when you change the filter.
 

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Discussion Starter · #5 ·
Nope, that's not normal. I can't see the video - says it's private.

Where do you have the throttle set when you're starting it? Also, you did not mention it, but be sure to check the air and fuel filters. The fuel shutoff at the fuel filter is notorious for breaking when you try to actually use it, so don't bother - only a few drops of fuel will come out anyway when you change the filter.
It doesn't matter where I set the throttle. I have tried different spots and it always stumbles for the first 20 or so seconds before it will smooth out. The filter isn't bad as the vacuum gauge is running about 10. I haven't gone the fuel filter route as the whole filter assembly and housing was new when I bought it but this is one of the last areas that I haven't replaced. I can't think that it is something major, given the issue goes away and the tractor runs just fine once it gets over the stumbling. I also changed the video to public.
 

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Discussion Starter · #7 ·
Sounds like the fuel injection pump governor is bad.
Would that go away on its own after a little bit? It hunts after starting and then stops and won't do it again. Even under a load it doesn't hunt.
 

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It does seem like a governor / injection pump issue, but I can't figure how that would go away after it warms up.

Is the fuel shutoff solenoid opening all the way? I'm thinking maybe it's getting weak, and 12V battery power alone is not enough to retract it, and then once it's up to speed and putting out 13+ volts it's OK. Yes, it's a long shot - if that's what's happening, you should be able to see it moving during the hunting period.

Other than that, I'm stumped - I guess I'd try changing out the fuel and air filters just for the sake of completeness, but without any expectation that's going to make a difference. My vacuum indicator never moves, not sure if it's actually working, so I just change the filter every year or so.
 

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Discussion Starter · #9 ·
I talked to the tech at the dealer and he thinks it is the injector pump. He said the timing on the pump changes as the engine warms up. He said it sounds like the starting position on the injector pump is misaligned.
 

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Nope, that's not normal. I can't see the video - says it's private.

Where do you have the throttle set when you're starting it? Also, you did not mention it, but be sure to check the air and fuel filters. The fuel shutoff at the fuel filter is notorious for breaking when you try to actually use it, so don't bother - only a few drops of fuel will come out anyway when you change the filter.

Sent from my iPhone using Tapatalk
 

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Clearances change as the fuel/pump warm. Could be the shutoff solenoid but I am thinking wear on the internal injection pump parts.
 

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Discussion Starter · #12 ·
The diagnosis came in from the shop. The plungers are stuck. It is going to be rebuilt.....at a cost but they guarantee it will function just like it did when it was new.
 

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Did they have any clues as to why things got gummed up? You didn't mention how many hours on the unit, but I wonder if the previous owner neglected to use a lubricity additive after they switched over to low sulfur fuel.
 

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Discussion Starter · #14 ·
After seeing how bad the sending unit looked in the fuel tank, I would say that it got water in the fuel at some point. The sending unit was all rusted and the fuel level arm actually fell off. The tractor only has 1200 hours and looks great but it ran like crap.
 
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