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Old 10-17-2012, 11:28 PM
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YellowDogSVC YellowDogSVC is offline
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"bad diesel" or what in Bobcat

Noticed after filling up my Bobcat s750 with Kubota v3800 that the power seemed to be "off". I didn't like the way the motor sounded either. It didn't sputter but it just sounded like it was missing (I'm at 500 hrs, all new filters, fluids) but rpms held steady. Just sounded "off" and the vibrations were different.

Was running fine until I put 17 gallons diesel from my local gas station where I always get fuel.

Here's what it does. When machine is moving, if I curl back the bucket or lift or hit the auxiliary circuit for my tilt tatch (when digging into a pile), the rpms drop significantly and it feels like a dog. The machine used to spill dirt over the top of the bucket before it started to stall.

Last week I had it serviced and they did a computer update but supposedly it was only for the EH controls. For about 8 hours, it had tons of power and then after the fill up.. it was a dog. Could Bobcat have "detuned" my machine the way the Cat C series was? My tech didn't think so..

Had a service call and they checked fuel. No water or contaminants visible. Changed fuel filter again to be safe. Checked psi on fuel lift pump and it was within specs but it still ran like crap. Tech suggested I let it burn off fuel and then top off with fresh fuel. I did that and put another 17 or so gallons in. I felt like it ran good for about half the day, then back to being a dog when it hit half a tank. That was my perception.

Anyone have a similar story? Could it be poor fuel? Any fixes other than draining tank? Additives? I have it on a job site and draining tank there would be a chore. I added some Lucas fuel conditioner yesterday but can't tell if it made a difference. Any help appreciated.
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Old 10-18-2012, 01:08 AM
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alldayrj alldayrj is online now
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I once accidentally half shut the petcock on the fuel tank while messing around servicing the machine. filled it with diesel and all good but dogged under load, somehow it was sucking fuel through it. but when it got down to half tank it got worse and worse down to a quarter where it stalled. kept filling it and running since I had to finish. Somehow it being full of fuel allowed it to run.

my point is, check the petcock, it could be something really dumb
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Old 10-18-2012, 12:33 PM
Tizzy Tizzy is offline
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sounds like a fuel delivery problem to me. i would check the shutoff ive done the same as above. i hit it while sevicing the machine and shut it partially off. and it felt like a dog. i would start stalling when lifting loads half the size of what i had done in the past.

also try running some diesel kleen injector cleaner through the thing. if it was some bad fuel this will clean it out. but the bottle that does 30 gallons and dump the whole thing ina new tank of fuel.
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Old 10-18-2012, 07:23 PM
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YellowDogSVC YellowDogSVC is offline
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So far we have narrowed it down to the lift pump. Replaced that. It is running good but it has run good for a few hours before acting up. Will try it out and keep others posted in case they have a similar issue.
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Old 10-18-2012, 09:05 PM
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BrandonV BrandonV is offline
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water in fuel?
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Old 10-18-2012, 09:11 PM
swanny swanny is offline
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I like Seafoam for injectors and dirty burning issues
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Old 10-19-2012, 10:06 AM
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YellowDogSVC YellowDogSVC is offline
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We couldn't find water in the fuel, filters were clean. The vacuum side of the lift pump wasn't up to specs. It sounded much better after we swapped the part out. Haven't had a chance to run the machine hard but will update the thread after I do. I have used seafoam and lucas. I like both. Seafoam seems to clean things a lot better. It also has some stabilizer qualities.

For those guys buying i Tier 4 machines and Tier 4 machines, clean fuel is going to be a big issue. I imagine there will be a lot of grumbling on the forums. The new engines cannot handle poor fuel. The fuel filters are more advanced but the system as a hole is less tolerant.

I personally am a little worried about fueling up in the field or moisture contamination in my transfer tank but I the some of the specs I've seen on the i Tier 4 machines show that fuel economy and power will be a little better. This is for above 75 machines like skid steers. I hope the fuel improvement offsets the extra $4500 that the iT4 and T4 enhancements will cost.
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