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losing engine rpm and stalling

43K views 44 replies 13 participants last post by  cristaz 
#1 ·
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.
 
#3 ·
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.
 
#4 · (Edited)
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.
 
#5 ·
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.
 
#6 ·
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.
 
#10 ·
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.
 
#12 ·
update

I picked the machine up from the dealer on Saturday. Unfortunately they could not get it to duplicate the issue. When I loaded it in the trailer to bring it to them is was having the issue. It took me a couple tries to actually get in into the trailer as it kept stalling. It took about an hour to get to the dealer. When I started it up there and unloaded it had started running fine again. The next day they got to it and ran it up and down the road numerous times but could not get the issue to show up. So they put some diesel fuel additive in the fuel just for good measure and gave it back to me. I've been running it for 2 full days now and haven't had the issue show back up. I'll post back if it loses rpm's again and I try a few of the suggestion.
 
#13 ·
I picked the machine up from the dealer on Saturday. Unfortunately they could not get it to duplicate the issue. When I loaded it in the trailer to bring it to them is was having the issue. It took me a couple tries to actually get in into the trailer as it kept stalling. It took about an hour to get to the dealer. When I started it up there and unloaded it had started running fine again. The next day they got to it and ran it up and down the road numerous times but could not get the issue to show up. So they put some diesel fuel additive in the fuel just for good measure and gave it back to me. I've been running it for 2 full days now and haven't had the issue show back up. I'll post back if it loses rpm's again and I try a few of the suggestion.
The only thing the additive would do might help it not gum up. Is it cold where you are? Are you running the right mix of diesel? Otherwise, someone drained the water in that filter and boom, issue fixed.
 
#14 ·
Mine is getting real bad now. I was snowblowing yesterday the temp was +10 Fahrenheit, used the block heater for a couple of hours before starting, but it still took 3 tries to start it.
The water temp after using the block heater was 135 deg. At that temp the glow plugs don't even come on.
My problem is like the others here, if I'm snowblowing at anything over 3000 engine rpm's it will just die out and almost quit, if I don't immediately stop moving forward, I wasn't going fast just creeping thru 8-10 inches of snow. I removed the cap on the hydraulic tank and got a small whoosh of air, but it didn't help at all, I tried it several more times during my snowblowing time but didn't get anymore whooshes. It feels like the hydrostatic drive is the issue, but towards the end of my hour and a half of blowing, it would start dieing off if I had it in park and ran the and throttle to 3600 rpm's. That sounds like a fuel issue.
I also early on dumped about twice as much diesel anti freeze stuff in the tank accidentally as I was supposed too, but it didn't help a bit over the next hour. I also use Irving diesel as their refinery is in Canada and every big diesel truck owner and the local schools love Irving diesel as they don't have winter problems with it. That and I already had some of the winter fuel treatment in it.
I noticed that someone else had about the same problem and replacing the fuel filter didn't help them.
Any one have some more suggestions?
 
#16 ·
No I haven't, I need to try that as mine seems to be fuel related, seems odd that so many are having about the same problem. We shouldn't all be having fuel problems. This is the first diesel problem I've had in any of my truck or tractor stuff I've had in the past 17 years.
 
#17 ·
fuel filter icing?

Did you use Diesel 911 or another treatment? Not all diesel fuel treatments are equal. Some have deicers, others have solubilizers, demulsifiers, etc.


Maybe it's a design flaw, making the unit more prone to fuel filter icing?
 
#19 ·
Diesel 911 worked for me. Seems like we are all having the same issues in cold weather. I wonder if it has something to do with the way the fuel is returned to the tank?? Diesel 911 (red bottle) is hard on injectors but gets rid of any water in the system. I keep a bottle in the door pocket just in case. Its going to be -30 windchill here this weekend, I'll probably add a splash tonight.
 
#21 ·
I just replaced my snow lowers broken pto shaft (see my other post on that, and no bobcat wouldn't cover it under warranty, even though the universal joint that broke was probably broke when I bought it). I tried snow blowing at low rpm's (3000 engine rpms) and it had no power at all and even creeping very slow it would die out and almost quit. Even just rotating the chute to the right at 3000 engine rpms killed it with no load. Turning the chute to the left is fast and no problem, turning to the right has always been very slow.
I drained the water separated and got nothing but fuel out of it, and the overdose of anti icing stuff I dumped in Sunday should of melted any ice that was in the system.
Now I have it in my garage with the propane heater blowing on it, I'm going to give it 2 or 3 hours of heat and see what happens.
 
#22 ·
I temporarily fixed it😃😃😃

I put it in the garage with 2 kerosene, and one propane heaters surrounding it for 3 hours.
Then I drove it up a hill about a 1/4 mile, it went up it at 18 mph just like it does in the summer. Turned around and came back down and continued on for about 3/4 mile at 27-30 mph just like it does in the summer.
When I swiveled the chute it turned quickly (although it still went slower to the right), and did not bog down the engine. We have about 80 community mailboxes where I get my mail and whoever is plowing it out wasn't pushing the snow back enough. So I spent half an hour with no problems snowblowing 2 - 2 1/2 foot deep hard packed snow. I am still very impressed with the power this thing has while blowing snow. I did hit a large chunk of ice and popped a sheer pin, so I zoomed home at 25-30 mph and spent about a half an hour finding my tools, sheer pins, and installing the new one while the Bobcat 3650 was running so the cab would stay warm, it was zero outside.
I backed it up and noticed it was a little sluggish, I then swiveled the chute to the right and it started bogging down the engine again while moving much slower than it had been. I think it must have too thick of hydraulic fluid in it. Is their a winter weight hydraulic fluid we can use??? Although I'm not ruling out fuel issues, it does seem to have a problem with the hydraulics in weather around 0.
 
#23 ·
I agree with temps from about 5 on down. I run a degel product beginning in October along with winter mix diesel and it seems to run fine once warmed up. Once outside in the cold, fuel gels quickly, and I'm not convinced the Yanmar handles cold weather very well. My neighbor has a new Ranger diesel with the Kohler and it seems to work much better in cold weather. I'm interested in your cold weather hydraulic fluid question.
 
#25 ·
I just bought some Bobcat all-season hydraulic fluid, it's supposed to be good to -40. I think it had the summer stuff in it that's only good to +40.
My problem is the manuals only show removing the hose from the hydraulic tank to the pump to drain the system, that looks like it only drains the tank (2.75 quarts), the system holds 8.4 quarts. How do I get the rest out, the shop manuals don't address that.
 
#26 ·
Update, I tried snow blowing yesterday, temp around 20f, it took 4 tries to start and was losing power and would hardly move itself. I applied heat to the fuel and hydro tanks and about an hour later drained the fuel filter again. (I have not changed hydro fluid yet).
It ran great, with tons of snowblowing power and went fast again. This afternoon with the temp at 10f and lots of freezing wind I went out gave it 2 glow plug cycles and it started right up with no stumbling or hesitating. I snow blowed some more with it and drove it about a mile at 25 mph, then let it idle for about 20 min. Then drove about a half mile home and snowblowed some more, it worked great.
It's getting down to -20f tonight, I won't be able to try it again until tomorrow night.
 
#27 ·
Very dumb question, but are you sure you are running winter blend for fuel? I live in MN, "some" of the gas stations, especially the Coop Gas stations don't have winter blended diesel in their tanks. The reason being is the people who go to them generally drive large trucks and etc and like to blend their own diesel.

It sounds like you are slightly gumming up for some reason. I live in MN, it was -14 yesterday and I was out in mine without any issues. Full power the entire time.
 
#32 ·
I have a new fuel filter on the way from my a Bobcat dealer.
The thing I did different this time was heating everything up nice and warm, then I drained the water separator.
I'm off work for the next week so I should be able to test it out some more.
My fuel is from the local Erving station, the refinery is in New Brunswick Canada about a hundred miles from us. They are known for having very good none icing fuel. Plus I had antigell stuff in it and then overdosed it some more.
 
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