losing engine rpm and stalling - Polaris Brutus Forum
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post #1 of 44 (permalink) Old 01-28-2015, 02:40 PM Thread Starter
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losing engine rpm and stalling

Need some help and ideas troubleshooting this problem. I have a 2014 brutus hd pto. I'm having an intermittent issue where driving normally it will suddenly lose engine rpms down to a bare idle. The machine will slow down, sometimes to a stop, then the rpms will come back up and it will drive normal again. The dealer changed out the fuel filter but that didn't fix it. Today the problem reappeared and this time the engine actually stalled completely. It would restart but not easily. The rpms were erratic and when I tried to go it was sluggish and stalled again. So I loaded it on the trailer and brought it back to the dealer about an hours drive away. When I dropped it off it was running fine again. Interestingly too is that if I used the hand throttle I could run the engine and rpms at full throttle with no issues. But when I used the treddle peddle to drive forward is when it would have the problems. Any thoughts on what may be causing it or things to check would be appreciated. Thanks, Jeremy.
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post #2 of 44 (permalink) Old 01-28-2015, 03:37 PM
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never had that problem yet, let us know what the problem is when you find out.
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post #3 of 44 (permalink) Old 01-28-2015, 03:49 PM
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Garage
My Bobcat 3650 was running erratic at startup last fall, the new fuel filter fixed that, but now that it's winter, it works great in low snowblowing, but if I try to drive down the road in high it is very sluggish and will get up to about 20mph and then just die out like the engine is lugging. It feels like the hydrostatic drive is fighting it, there just isn't any power while driving fast, but all kinds of power for snowblowing. Also the snowblower chute swings left real fast, but just creeps when swung to the right, in warm or cold weather, although it's slower in cold weather.
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post #4 of 44 (permalink) Old 01-28-2015, 07:40 PM
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Ive found that my machine will sometimes bogg down and that letting up on the treddle a bit would bring the rpms back up. Bogg is maybee not correct its more like idle down as i dont feel the rpm drop is caused by a load but more a throttle controll problem. I'm trying to nail down more of a pattern on what conditions cause this but I think its related to hyd oil temp or flow or lack thereof.

perhaps there's some sort of govenor that relates flow, rpms and throttle position. if the hyd flow drops for some reason the engine idles down to prevent damage to the pump.

I don't think its a "normal" condition but I have had others describe the same thing on other hydrostatic machines like tractors.

Last edited by TheRealBuzz; 01-28-2015 at 07:47 PM.
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post #5 of 44 (permalink) Old 01-28-2015, 08:59 PM
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Try unscrewing the hydraulic fluid cap and equalizing the pressure. Had a similar issue last winter and unscrewed the hydraulic fluid cap. There was a rush of air into the tank as the pressure equalized - I guess the fluid level dropped over time and simply opening the cap eliminated the problem. Maybe it's driven by big temp changes?

One thing I noticed is that I could run the brutus at wide open throttle while still, and the bogging down issue only happened when I was moving. That's what pushed me to check that cap.
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post #6 of 44 (permalink) Old 01-28-2015, 10:19 PM Thread Starter
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Thanks for the thoughts and ideas. Keep them coming. It seems that I'm not alone in this issue. Collectively maybe we can find the cause. Mine is exactly as each of you have described. I think its just a difference in how we're describing what's happening. As Jorts pointed out, mine was the same in that sitting still I could run the engine at full throttle either with the hand throttle or by pressing the treddle peddle while it was in park/neutral, but the problem presented only when it was in low or high gear and moving. TheRealbuzz mentioned something I read also about some sort of governing system to where if the hydraulic pressure drops the computer will take over the engine rpm and regulate it to prevent pump damage. Maybe someone can add some more information on this system and how its supposed to work and how to possibly bypass it temporarily to be able to rule it out. And as Ketchn said, I used mine all day yesterday with the snowblower with no problems. Again it was in low gear moving forward slowly with the hand throttle set up to about 2000rpms for the snowblower and it ran fine all day with no issues. Then the problem presented today when I was trying to go forward at full speed. Seems logical to suspect there's something going on with the computer systems management of the engine rpms relating to the hydraulic flow when the machine is moving.
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post #7 of 44 (permalink) Old 01-28-2015, 10:23 PM
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Did you try the cap trick? Curious if that worked...
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post #8 of 44 (permalink) Old 01-29-2015, 01:49 PM
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Did you try the cap trick? Curious if that worked...
Good suggestion, interested in knowing if this worked or not. Keep us posted!



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post #9 of 44 (permalink) Old 01-30-2015, 08:50 AM
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When you experience the loss in RPM what was the outside air temp? I had a similar problem and it turned out to be water in the diesel. It happend twice to me, both times the outside temp was less than 5 degrees. I used Diesel 911 additive and have not had a problem since.
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post #10 of 44 (permalink) Old 01-30-2015, 11:26 AM Thread Starter
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Its still at the dealer so I haven't been able to try anything myself yet. I'll let you all know what they find and say. The first few times it happened the outside air temps were 30's to 40's. At that time the dealer suspected water in the fuel filter / water separator so they changed it out. Seemed to run fine after that for a few weeks. When it happened again the other day temps were in the teens. It's only been 3 weeks since the filter was changed. I've only used it about twice a day to run to the bus stop since then and a few hours plowing the driveway. Then I used it for about half a day blowing snow on Tuesday. It ran fine all day Tuesday but it was high rpms set with the hand throttle and slow speeds as I was blowing snow. Then Wednesday morning when I went to the bus stop, high gear and high rpms using foot tredle peddle, is when the problem reappeared and this time worse then the first times it happened. I turned the drain lever on the bottom of the filter/water separator and checked what came out. All fuel and no water. Drained the entire filter. Then tried driving again. The problem was still there. I'm only using good clean fuel from a reputable gas station. I did treat the fuel with Bobcat brand diesel deluxe fuel additive. I used to use it with my t300 and had a bottle left over. I can't imagine that would cause any issues. In fact it should help.
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