Fuel and Vacuum Line Routing (16V N/A 944s)
How the fuel supply, fuel return, and primary vacuum lines route on 16V normally-aspirated 944S and 944S2 models, with a note on active-carbon-tank routing.
Introduction
This page describes the fuel and primary vacuum line routing for 16V normally-aspirated 944 models (944S and 944S2). The architecture mirrors the 8V cars; the main difference is operating pressure — the 16V system runs at a nominal 3.8 bar55 psi regulator pressure rather than the 8V's 2.5 bar36 psi.
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 8V cars, the 16V 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. (On 16V cars the fuel-rail service cap sits on the side of the rail nearest the intake manifold, between intake runners 1 and 2.)
- Return. The fuel pressure regulator at the rail bleeds off the excess and returns it to the tank. On the 16V the regulator holds the rail at the higher 3.8 bar55 psi.
Vacuum Lines
The primary vacuum connections are the same in principle as the 8V cars:
- Fuel pressure regulator. A vacuum line from the intake manifold lets rail pressure track manifold vacuum, holding the pressure drop across the injectors constant as load 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.