Sultan, thanks for the detailed response. Interesting and helpful information!
This Hitachi 270 has good power, even at partial throttle. It pulled about 20,000 yards of heavy blue clay out of a pond and had no problem digging that using a two yard clean up bucket. I rarely use the smaller bucket with teeth, since the machine handles the large bucket well.
I should get a tach such as the type you suggest or a laser tach. It also occurred to me that an easy way to get a rough idea of the engine RPM might be to time the swing time for the machine. This machine is supposed to do a full 360 degree turn in about 6 seconds at full throttle. At the speed I usually run it at, it takes a little longer than that.
Because your computer isn't working, your pump has become a fixed displacement pump that always runs at 70% of max flow. Thus, the behaviour of your machine will be very different compared to mine.
Just a bunch of points:
-Because of the pump running at 70% of max flow, the swing speed would be slower. If a 360 degree swing was supposed to take 6 seconds with a computer, it would now take about 8.5 seconds without the computer.
-The advantage of having a working computer is that you would have faster cycle times and lower fuel consumption in lighter digging
-Another advantage of having a working computer would be that you would burn much less fuel doing jobs like stump pulling, where you need high pressure and low flow. Without a computer, the pump would be wasting energy pumping a high volume through the relief valves.
-Computers are not as great as they say they are. In heavy digging like pond work, you're better off WITHOUT a working computer.
-On my excavator, the arm crowd was very slow in economy mode because the computer was reducing the swashplate angle of the pump in my excavator. This caused the pump to pump very little and the machine to dig very slowly,
-When the computer doesn't work, the pump holds its swashplate angle and makes full use of the engine torque to get all the power to the bucket no matter what. Thus, your machine is able to fill a 2 yard ditching bucket at around 1/2-2/3 throttle. If you fix your computer, you will find that it would struggle to fill a 1 yard toothed digging bucket at the same throttle level, because the computer will decide that it doesn't want to load the engine and it will reduce the pump flow to almost nothing.
-This computer phenomenon is much worse in newer excavators because of all these emissions regulations. When diesel engines are put to work, they like to make a little black smoke, and even the tiniest bit of black smoke kills environmentalists. Thus, the computers in modern excavators shy away from even going near the engine's max torque. And so, the pumps decide to play dead when you get into tough digging. It's why some people still hang on to their old Koehrings and such. In heavy digging, new fancy low emissions machines simply cannot compete with the brute force of the old fixed displacement, computer-free excavators.
P.S. The pond I was digging in had some real intense conditions. I was digging in a mix of sand and gravel, and as you may know, wet sand/gravel mix is the densest stuff you ever dig. To make matters worse, the pond had a 1/2" thick solid carpet of some impossibly tough moss that really worked my excavator to tear it.
