Fuel Delivery and Air Induction: Description and Operation

MOTRONIC FUEL SYSTEM

FUEL TANK AND PUMP

The Motronic fuel system for the 4.2 liter V8 is equipped with a 21 gallon fuel tank mounted under the rear of the vehicle. An electric fuel pump that is mounted inside the tank pumps fuel through an externally mounted fuel filter to the rest of the fuel system.

FUEL PUMP RELAYS

This system is equipped with two fuel pump relays wired in parallel, the purpose of the second (redundant) relay is to ensure reliability. Both relays have similar alpha-numeric identification in the wiring diagrams J17. J17/1 is located on the fuse/relay panel. J17/2 is located on the auxiliary relay panel.

FUEL RAILS AND PRESSURE REGULATOR

The in-tank mounted fuel pump delivers fuel to the fuel rails. Fuel is distributed to the injectors via the fuel rails. A fuel rail mounted pressure regulator maintains fuel pressure at the injectors so there is approximately a 58 psi (4.0 bar) pressure difference to the intake manifold pressure. The intake manifold pressure influences the fuel pressure via the pressure regulator. This ensures that the difference in pressure between the intake manifold pressure and the fuel pressure remains constant.

FUEL INJECTORS

The fuel rail mounted injectors are solenoid-type four hole two spray versions. This configuration prevents puddling in the land area between the intake valves.

Each injector has its own connection pin at the Motronic engine control module. This allows the ECM to recognize a fault in a single injector, although the injectors are still activated in pairs. Power is supplied to the injectors via a thermal fuse located in the fuse/relay panel. A separate output stage (switching unit) located inside the Motronic ECM is provided for each injector. The output stages are used to complete a ground circuit for the injectors. Multiple output stages are necessary for sequential injection and fault diagnosis.