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Nissan QR25DD

Nissan QR25DD 1

Without keyword

High Pressure Fuel Pump, engine QR25 DD

QR25 DD engine

Injection pump is not much different from the pumps installed on engines of the VQ series. Structurally, there are several differences flawed for the pump. These changes have affected the longevity of the injection pump as a whole. Service life now depends on the quality of rubber and fuel. Pump repair is not provided by the manufacturer. All details are “one-time”. This is a big minus of developers.

General view of the pump.
Photo 1

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The standard pump drive transmits torque from the camshaft.

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The pump drive has a beveled plane, which allows rotation
pressure on the plunger.

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The drive with a shaft in the pump body rotates on two bearings

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Bearing lubrication is carried out with engine oil, which is undoubtedly a plus. But with poor engine maintenance, this lubrication method can destroy the pump. The lubrication channel is very thin and easily clogged. A rotating drive sprays oil along the walls of the pump, separating and accumulating hard particles of oil in the pump cavity. This is a kind of centrifuge. Over time, dirt builds up and destroys the structure.

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“Pumping” of pressure is carried out by three plungers that are installed in a fixed drum. In the drum, the fuel and oil chambers are separated. The plungers are mounted relative to each other from the center by 120 degrees, which allows to obtain uniform pressure during rotation of the actuator. On similar pumps of engines of the VQ series, a dividing corrugation was used. On the same pumps there is no corrugation, and the separation of the chambers is carried out using glands.
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The drum is inserted very tightly into the pump body. Separation of oil and fuel channels with rubber rings.

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Pump repair is not provided, therefore, there are no threaded technological holes in the drum for removing the drum. The drum can be removed only with a specially made puller, through the low-pressure chamber (center hole). Fuel to the pump comes from the first pump through the intake screen and enters the low pressure chamber. Low pressure of about 4 kg.

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Smoothing pulsations of low fuel pressure by a damper .
Photo 12

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Fuel enters through the central hole in the drum into the supraplunger space. The plungers have side openings for receiving fuel and check ball valves inside.

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During operation, wear of the working surface and a marked decrease in pressure. Due to the increase in gaps.

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The check valve in the plunger is large enough and collapsible. Therefore, it is possible to clean and check for leaks..

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When pressed, the plunger pushes a portion of fuel into the high-pressure chamber. Additionally, ball valves are installed in the chamber to separate the pressures. Operating average high pressure is about 80 kg.

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Pressure control is carried out using the solenoid valve of the regulator. It is also controlled by the engine control unit. The regulator has a grid for filtering fuel entering the injectors (additional barrier for dirt and protection)

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Even after ultra sound cleaning, the mesh does not clean well.
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The pump provides additional mechanical protection against transmission (controller failure). Pressure valve installed in plunger drum housing.

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When emergency pressure occurs, fuel is vented to the low pressure chamber.

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A distinctive feature of this type of pump is the use of separation seals. The developers reduced the size of the pump, but greatly reduced its service life. When working with dirty oil and fuel, wear of the oil seals occurs very quickly. Rubber is erased and there is a possibility of fuel leakage into the oil. And this, in turn, can lead to ignition or destruction of engine mechanics.

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In conclusion, I would like to note that this design of the pump is quite reliable. Although highly dependent on the quality of the oils and fuels used. With proper maintenance and prevention, the pump resource can be significantly increased. Maintenance costs are small; it is enough to check the contamination of the nets, change the filters, control the presence of gasoline in the oil and prevent the engine from overheating.

All successful repairs
Vladimir Bekrenyov


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