Just had a warranty engine replacement on my KX91 and after about 7 hours the machine will no longer do anything but low idle (around 700rpm). Info: The auto idle selection doesn't do anything The idle low/high idle doesn't change anything. Manually moving the throttle near fuel injectors actually causes the engine to die instead of rev up. thought it may be the fuel filter, which is new, so I took it off but noticed nothing. I didn't cut it open but it looks clean. I checked the injectors, slightly loosened and diesel came out as expected, so it's getting fuel there. Next thought is that it's getting air in the line somehow. I've looked everywhere and the only suspect part is near the on/off water separator and the fuel on/off valve. The input and output fuel lines go into metal aluminum elbows that are loose. Both will come out with a light tug. The Kubota dealer says tht this type of thing is not unusual but they are not sure that would cause the problem. To test, I bypassed the system all together. I then let the system fuel prime pump run for a while to make sure any air gaps were pushed out but no luck. Turned the engine on and it goes right to low idle and stays... Unfortunately the excavator doesn't have enough power at 700rpm to load on the trailer, so I can't just take it in to the shop. Any ideas?
You can vacuum test from the tank to the engine. If it holds vacuum indefinately it may just need bleeding. Or the pump was not shimmed correctly
The auto idle switch has to have a fuse protecting it. Have a look at the fuse box and check all the fuses for power on both sides. was it a factory new motor and pump?
What I don't understand is why kubota isnt comming to you and fixing their screw up. Was it a complete motor, long block, or short block replacement? Is the exhaust clean or is it smoking heavy, is the motor running smooth at idle? Thinking to myslelf that pump timing might be off, or injectors may have been damaged if the old head was re-used. I have seen where injectors tips were ruined by incorrect removal / install of the head
When you say bypassed, what do you mean? I think you have an air leak as you suggested, but I would have thought you'd get a 'slight' change in RPM when you move the throttle. Those elbows should be tight imho...If absolutely no change in RPM, then it sounds electrical as 74" said.
Bypass I took the input hose and connected it directly to the output hose, bypassing the on/off value with the water separator. But ya, I also expected some idle delta. I also expected that when I manually moved the throttle it would do something but die. Generally it idles smooth unless I screw with the manual throttle. Messing with the throttle just a little will get the thing to pulse from 700rpm up to around 900rpm for about 30seconds, then it resumes the normal idle. I checked some of the fuses but ill go check them all to make sure. -Sert
Yeah, I was thinking of a diesel can with the output hose in it and taped (primer bulb on it) to rule out tank/filter issues. Does your throttle have some sort of electronic component to it? I hear in diesel trucks they have the exact issues you do, and it is related to an idle position sensor or WHY....
The loose aluminum elbows are probably your problem. I have 7 of those machines and have replaced 5 water separators. That solved the problem in every case. To test it, put a bead of JB Weld around where the elbows go into the body of the filter base. Let it harden and then it should run fine. If it does, replace the filter unit. I tried the JB Weld fix. After a short time, the engine vibration broke it again.