1999 580 SL Series 2. Using a 3 ft. bucket and digging in dirt that's not particularly hard digging, it seems like it would lose a lot of RPMs when the bucket was near to getting full. I was running about 1,600-1,800 RPMs while digging. Any thoughts on what to check?
Why are you only running your engine at 1600-1800 rpms? All systems are to be run at full throttle to meet peak hydraulic performance with the peak torque curve of your engine. Bump up to full throttle and see if you have the same problem.
I didn't know I was supposed to run at full throttle. I've never seen anyone run a backhoe at full throttle while digging.
The metering designed into the valve spools is actually built to work best at full flow, and hydraulic pumps tend to be most efficient at rated speed. Most experienced hoe operators I've been around at least, the first thing they do after the seat spins around is yank the throttle wide open and then get to work. The exception of course is a situation where it my be better to slow things down a bit.
1,600 -1,800 rpm your hoe should not be losing much rpm unless your digging a deep trench or large hole there's not need to run wide open especially if your the one buying the fuel & paying for the repairs. As for the reason it's losing a lot of rpm maybe the dirt is harder than you are aware of or there's something else going on.
I should specify that I've dug in this same area and same depth several times before and the machine did fine. It seems as though it has gotten a little weaker more recently. I'll try it at full throttle next time and see what happens.
When is the last time you changed the fuel filter? You may have a blockage there or water issues. A 3" bucket is pretty heavy for a machine this size. I use about the same hoe but a 416 CAT with a 3' bucket a lot to move and grade as I go. They pull hard. Change your filters if you have not , also I think there is a screen in the fuel inlet for the pump that can get plugged. And I agree , its a good Idea to pin it back toward w o t when digging. I think its easier on the machine just slow your control movements down. Those are good backhoes.
Fuel filters have 300 hrs on them, book says to change at 500 hrs. I should check the screen on the fuel inlet, haven't checked that before.
Do you notice more or less black smoke than before the loss of power, and does it drive up hills the same or weaker than before you noticed the loss of power? 1,600 -1,800 rpm should be plenty of power IMHO. Just above the peak torque.
I haven't seen any black smoke at all. It does seem to drive worse up hills than it did before, but it was never great in 4th gear anyway.
Sounds like you're on the right track with #8, or any of the rest of the fittings in the fuel system.
On a semi-related issue, the hand throttle has been getting stiff. Any areas of the linkage to check that could be the likely culprit? The foot throttle seems fine.
You can take is apart clean it, adjust the friction washer but do not lube it.
Although the filters may have only 300 hours on them does not mean conditions may have developed that would warrant changing them now.