Fuel pump

Design and Function

Applies to: 2000–2004; B4164S2, B4184S10, B4184S2, B4184S3, B4184S9, B4194T2, B4204S2, B4204T2, B4204T2 CVVT, B4204T3, B4204T3 (CA) (US), B4204T4, B4204T5

Introduction

The fuel pump, fuel level sensor, and pressure regulator are installed in a single unit in the fuel tank. A spring is used to press down the unit against the tank's bottom, to absorb tolerances and changes in tank volume.

Quick-couplings are used in several places in the fuel system, e.g., by the pump unit, as well as pressure and return lines. No special tools are needed to open the couplings.

The fuel system can be drained in the same way as for S70/V70/C70, by using a special tool through the drain valves.

Function

The pump sucks in fuel mainly from the reservoir, pressurizes it, and leads it into the pressure line.

The return fuel is used to get fuel in to the reservoir. The return line ends in a restricted outlet, giving the fuel a high flow rate. This creates a low pressure in the reservoir's suction line, which means that fuel flows in to the reservoir from the fuel tank.

In reality, this arrangement means that pumping is done in two steps, first from the tank to the reservoir and then from the reservoir to the pressure line. Also, this minimizes the risk of air bubbles when cornering or when driving on steep grades with only a little fuel in the tank.