kobelco 295 mark 8 crank but no start

Hey everyone! Just found this place and figured I'd join up.

I'm working on a Kobelco 295 Mark 8, serial # u0818, and it's cranking but won't start. The pumps are hitting 4000psi during cranking, the PSVs sit at 350mA, and the unloads are at 750mA. Here's the weird part—the engine fires right up when I unplug any sensor or solenoid on the pump or hydraulic components. I noticed that unplugging the travel pressure sensors on the pilot side makes the unloads drop to 0mA. I've cleaned all the ground connections and there's no fault code showing. Each time I disconnect something to get it started, the related code pops up but nothing else. Any ideas what's going on here?

Not many people have experience with Kobelco excavators, so hopefully someone else will jump in. I'd suggest pulling and opening up the hydraulic filters to check if something's broken down inside them.

When I run the machine, everything works fine. The only issue I see is that stick OUT loads the pumps up to 4000psi regardless of demand, whether I move fast or slow.

Does anything show up on the display? From what you're describing, it sounds like a low-pressure sensor might be throwing an error. When that happens, the controller thinks there's an active operation going on, so it pushes the pump swash plate to full angle. That overloads the engine and stops it from starting.

No error showing on the display unless I unplug something to make it start. We had a timing issue at first—the wheel on the crank pulley was broken, so we replaced that. Then we thought it might be fuel, so we swapped out the aftermarket fuel lines. But now it looks like maybe a computer misread or a crossed signal from somewhere, though it's hard to pin down exactly where. Looking through the monitor data, nothing obvious is jumping out as a bad sensor. The unload solenoids are at 750mA when everything's plugged in normally. But when we unplug certain pressure sensors, one or both of the unloads drop to 0mA and the engine fires right up.

Look closely at both unload valves—even if they're electrically fine, they might be stuck mechanically. Keep an eye on the two bypass-cut lines since they work opposite to the unload valves. When you unplug the low-pressure sensor, the controller sees an electrical fault and switches to backup mode. That's when the main hydraulic circuit gets vented through the bypass-cut valve, which drops the load and lets the engine fire up.

Thanks for the clear breakdown and the photo.

That makes sense—so at 750mA, pressure should be hitting the unload valve and bypass-cut entrance. I've seen setups where they T a line to the solenoid too. But would the machine actually run okay if those got stuck or partially stuck? I've noticed that when they stick, the pump loads up to 4000psi no matter what the demand is.

What readings are you getting on your pilot pressure sensors with the key on but engine off, and then at idle when nothing's running? Same question for the high pressure sensors on the pump.

All the readings are coming in within reasonable range and the electrical signal checks out. I confirmed the pressures with a gauge too. What's got my attention is E-3 and E-4, the optional relief valves 1 and 2 - they're stuck at 3146psi no matter what I try. The solenoids are running around 265-310mA, same ballpark for the measurement. When I unplug the solenoid, the measurement drops to 0mA, but then it shows 2900psi, which I'm not sure where that's coming from.

Those two parameters are just the settings for the safety discharge pressure control solenoid valve, which is an optional feature. A technician can adjust them however they want. Like you can see, they're the solenoid control current converted into a pressure value. They don't have anything to do with your no-start issue. But if parameters B16 through B19 are already showing an effect before you do anything, that could be worth looking at.