HITACHI ZX350LC-3 ENGINE BOGS DOWN

Hello, I have a ZX350 LC3 (6hk1 eng.). The engine runs good. When I try to use the boom/bucket in any way especially two functions at once the engine bogs down , sometime almost to a stall, and it will also barely walk. Engine / turbo work good. I have replaced all filters.

I was told it may be a sensor on the pumps but unsure were to begin looking. Any help would be appreciated.

None of the sensors on the pump would cause this issue. It sounds as though the pumps are not backing off enough. The pumps are basically regulated by their own pressure. As each pump pressure rises, the delivery pressure is routed up to the pump regulators to back them off.
Are you 100% certain the engine is performing ok?
Does it look like any of the adjustment screws on each of the two regulators have been adjusted?
Have you done any troubleshooting on it with MPDr? Any fault codes, monitoring values, pressures etc??
Lastly, there's a torque solenoid fitted at the right side of the pump housing with a hose going to the right hand regulator with a link pipe going to the left pump. If the engine actual speed goes lower than the target speed this solenoid should activate and back the pumps to prevent engine stall. The higher the pressure from the torque solenoid, the lower the flow from the main pumps. Maybe worth putting a gauge in this line and reading the pressure when loading the hydraulics up. It should vary between 0-40 bar.

Unsure if this issue was there before. I just bought the machine and replaced the engine (sat 1 year). Old fuel was drained, new put in along with new filters. Engine runs good but I will recheck again. I assume that you mean fuel pressure. Thank you Gary.

I assume he was talking about the torque solenoid system pressure.

Does it smoke when it bogs down? or can you hook up a line and a gauge to the intake manifold to measure turbo boost while it's bogging? Either of those will give you a better idea if it's the engine running out of fuel, or the hydraulics overloading the engine.

I get the sense that You and Gary think I should start with the engine. I will check exhaust smoke and/or turbo boost with a gauge tonight. When I put the gauge's on what should the numbers be at idle and under load or should it be a certain number/percentage drop if any in the gauge number ? Thank you Delmer.

Update : Engine is working as should. At idle with no load, functions seem to work the best, anything over 1/2 throttle the larger function like boom and stick ( not hyd thumb or swing) go into a bind especially both at once and also going both ways. Pressure seems to build and get worse until either controls are let go engine stalls out. Seems like it almost will not let the fluid out of "the other end" of the pistons ???

trip said:

Seems like it almost will not let the fluid out of "the other end" of the pistons ???

Click to expand...

It's possible for one valve spool to break, but almost impossible for two to break at the same time. Much more likely to be something involved in the pump controls, which I can't help you with. That's why I asked about the engine.

"Working as it should" doesn't inspire a lot of confidence for me. I'd like to see some visible smoke as it bogs down, even and no white or puffs, a strong stream of smoke. The turbo pressure is probably 0 at idle and you should be able to reach 10-20 at full speed full load, the number should be in a manual, that's my guess.

I'm not saying it's the engine, that's just the easiest thing to check. Gary obviously knows the hydraulic system, so follow his suggestions.

Sounds like a fuel strainer screen is clogged there is one in a banjo fitting near pump or one of the supply lines...

trip said:

Update : Engine is working as should. At idle with no load, functions seem to work the best, anything over 1/2 throttle the larger function like boom and stick ( not hyd thumb or swing) go into a bind especially both at once and also going both ways. Pressure seems to build and get worse until either controls are let go engine stalls out. Seems like it almost will not let the fluid out of "the other end" of the pistons ???

Click to expand...

That's a strange issue indeed. It's unusual for the engine to perform ok at low idle but then stall at high rpm. Just so i understand. Your saying that at low idle, when you raise the boom, pull the arm in/ out, use the bucket etc the engine holds it's rpm. But when you increase the rpm above half, and do the same tests, the engine will pull down and eventually stall? Or do you mean when you stroke each service until it strokes to its end point it then stalls the engine? I'm just trying to understand what sort of load (pressure) you have on the pumps.
The first thing i'd do is check pump 1 and 2 pressures when relieving the boom/ arm/ bucket etc. The setting for those services shouldn't be much more than 350bar.
It's hard to diagnose because i'd usually be using diagnostic software.

Update ; After checking (apparently not) everything, Nortrax came out with the software and after 3 hours found the issue. The short story was the engine wire harness plug had something in it. It plugged in but not a great connection. Thank you everyone for all your input.

Thanks for the update. It's always nice to hear the actual fix, especially with the real head scratchers.