# Hitachi ZX350LC-3 Excavator Repair – Low P1 and P2 Pump Pressure

> Hitachi ZX350LC-3 loses power at idle and slows down when hot. Diagnosis: noisy pump, low P1 and P2 pressure. Main pump removed on site, no low-loader.

![Hitachi ZX350LC-3 hydraulic pump being lifted out of the machine compartment on a sling from the service van crane](https://wibako.com/media/articles/article-915/slot1-c-a2188820.webp)

The call was short and to the point: at low revs the machine is unworkable, at full throttle it runs "sort of OK", and once it warms up it slows down noticeably. The machine was a Hitachi ZX350LC-3 crawler excavator. Here we describe what our mechanic checked, why the decision was made to remove the main pump, and how we took it out on site without hauling the machine to the workshop.

Symptoms like these are a textbook sign of a hydraulic system output problem. However, not every excavator that "has no power" has a failed pump, which is why the decision is always preceded by diagnostics.

## The machine and the customer's complaint

![Hitachi Zaxis 350LC crawler excavator with open engine cover, side view](https://wibako.com/media/articles/article-915/slot14-c-bb860c1b.webp)

According to the nameplate, this is a 2009 Hitachi ZX350LC-3 with a 202 kW engine and an operating weight of 34,400 kg. It is a typical heavy earthmoving machine whose hydraulic system works under high load all day long.

The customer described three symptoms:

- at low engine speed, operating the attachment is practically impossible,
- at full throttle the excavator works, but noticeably weaker than it should,
- once the machine warms up, all movements slow down even further.

## Why an excavator loses power at low revs and when hot

The main pump in this class of excavator is a variable-displacement tandem axial piston pump. Its flow depends on engine speed and swashplate angle. As the pump wears, clearances between the pistons and the cylinder block and on the valve plate increase, and internal leakage grows with them. Instead of reaching the actuators, part of the oil returns to the pump case.

At low revs the pump delivers little oil, so leakage makes up a large share of the flow and little is left for actual work. At full throttle the higher flow partly masks the problem. Once warm, the oil thins, leakage increases and the machine slows down. We cover this in more detail in our articles [Machine losing power when warm?](https://wibako.com/about-us/blog/696-is-your-machine-losing-power-after-warming-up-excavator-loader-bulldozer-crane) and [Why does a machine lack power?](https://wibako.com/about-us/blog/695-why-is-the-machine-lacking-power-excavator-crane-loader-bulldozer).

## Diagnostics: noisy pump and low P1 and P2 pressure

![Tandem hydraulic pump mounted at the engine of a Hitachi ZX350LC-3 excavator, top view](https://wibako.com/media/articles/article-915/slot4-c-b7eecbe1.webp)

On site, the mechanic found two things: a noisy pump and low pressure on both sections, P1 and P2. Each section feeds its own part of the control valve. If pressure were low in only one circuit, the cause could be sought in a specific valve or actuator. A drop on both sections at once, combined with pump noise, points to the pump itself.

Based on this, the decision was made to remove the pump. The exact cause of the pressure loss and the condition of the internal components can only be assessed once it has been stripped down.

## Removing the hydraulic pump on site

![Pump compartment of a Hitachi ZX350LC-3 with hydraulic pump suction pipes, drum for drained oil below](https://wibako.com/media/articles/article-915/slot12-c-543038c1.webp)

Before the pump was lifted out, the hydraulic oil was drained into a drum and the suction, pressure and pilot lines were disconnected. The pump sits in the compartment behind the engine, coupled to the flywheel, so access is from above through the open cover.

We lifted the pump with the hydraulic crane mounted in our service van and took it out on a webbing sling directly from the machine's compartment. The excavator did not need to go to the workshop on a low-loader.

## Mobile excavator service – crane in the service van

![Removed excavator hydraulic pump in a drip tray in the service van under the arm of a red crane](https://wibako.com/media/articles/article-915/slot3-c-79216ae3.webp)

The main pump of an excavator this size is heavy and awkward, and removing it from the compartment by hand is dangerous. The crane in the van lets us lift it out, set it down in a drip tray on the van floor and take it to the workshop in one go.

For our mobile construction equipment service, travel is charged at PLN 3 net per km, counted both ways. A mechanic's labour hour costs PLN 230 net. The general scope of our work on machines of this brand is described on the [Hitachi service](https://wibako.com/about-us/service/732-hitachi-service-professional-repair-of-hitachi-loaders-and-excavators) page.

## What happens next with the pump

The next step is to strip the pump and inspect the pistons, cylinder block, valve plate, bearings and regulators. This determines whether the pump is worth rebuilding or should be replaced. We discuss typical faults and pump service intervals in the article [How often should excavator pumps be serviced?](https://wibako.com/about-us/news/817-how-often-should-excavator-pumps-be-serviced-rebuilding-a-dpvo-165-from-a-liebherr-a316). We described a similar job on a much larger machine in our article on [installing pumps in a Hitachi ZX870](https://wibako.com/about-us/news/833-one-small-thing-stopped-an-85-tonne-giant-installing-pumps-in-a-hitachi-zx870).

If your excavator loses power at low revs, slows down when warm, or the pump is louder than usual, get in touch with us. It is better to check the pressures before a worn pump contaminates the whole hydraulic system with metal particles.

## Frequently asked questions

### Why does an excavator slow down when the hydraulic oil gets hot?

Hot oil has lower viscosity, so internal leakage in a worn pump increases between the pistons, cylinder block and valve plate. The pump delivers less oil to the actuators and cannot hold pressure, so attachment movements and travel slow down noticeably.

### What does low P1 and P2 pressure mean on an excavator?

P1 and P2 are the pressures of the two sections of the main tandem pump, each feeding part of the control valve. If both pressures are low and the pump is noisy, the cause is primarily sought in the pump itself rather than in a single circuit.

### Can an excavator hydraulic pump be removed without taking the machine to a workshop?

Yes. On the Hitachi ZX350LC-3 described here, the pump was removed at the customer's yard and lifted out with the crane mounted in the service van. The excavator did not need to go to the workshop on a low-loader.

### Can a worn hydraulic pump be rebuilt?

WIBAKO rebuilds hydraulic pumps and motors. Whether a rebuild makes sense depends on the condition of the components once the pump has been stripped down.

### How is travel charged for the mobile service?

Travel is charged at PLN 3 net per kilometre, counted both ways. A mechanic's labour hour costs PLN 230 net.

Published: 2026-10-28

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Source: https://wibako.com/about-us/news/915-hitachi-zx350lc-3-excavator-repair-low-p1-and-p2-pump-pressure
Contact: +48338704200, biuro@wibako.pl