Fuel and Vacuum Line Routing (944 Turbo)

Introduction

This page describes the fuel and primary vacuum line routing for the 944 Turbo. The Turbo is an 8-valve engine, so its fuel system follows the same layout — and the same nominal 2.5 bar36 psi regulator pressure — as the 8V normally-aspirated cars. The turbocharger's boost plumbing (charge pipe and intercooler) carries air, not fuel, and is covered separately.

Cars fitted with an active carbon tank for fuel-tank venting carry additional vacuum routing for that system; it is similar to the carbon-tank routing described for the 8V cars in FUEL-13. Heater control valve and ventilation vacuum routing is common to all 944 variants and is not covered here.

Fuel Lines

Like the other 944s, the Turbo fuel system circulates: the pump delivers more fuel than the engine uses, and the surplus returns to the tank.

• Supply. The in-tank fuel pump draws from the tank and pushes fuel through the fuel filter to the engine compartment, into the fuel damper and the fuel rail that feeds the fuel injectors.
• Return. The fuel pressure regulator at the rail bleeds off the excess and returns it to the tank, holding the rail at the nominal 2.5 bar36 psi.

Note: On the Turbo, the fuel pressure regulator's reference is taken so that rail pressure rises with boost — keeping the pressure drop across the injectors constant under positive manifold pressure, not just under vacuum.

Vacuum Lines

The primary vacuum connections are the same in principle as the other 944s:

• Fuel pressure regulator. A reference line to the intake manifold lets rail pressure track manifold pressure, holding the pressure drop across the injectors constant as load (and boost) changes.
• Brake booster. A large vacuum line feeds the brake booster from the intake manifold.
• Evaporative charcoal canister. On cars with the active carbon tank, a line connects the tank's vapor system, through the charcoal canister, to the intake — purging stored vapor into the engine.