GM Cavalier/Sunfire 1995-2000 Repair Guide

General Information


On the 1995 2.3L engines, the fuel system is a multi-port fuel injection (MFI) system. The MFI system is controlled by a powertrain control module (PCM) which monitors engine operations and generates output signals to provide the correct air/fuel mixture, ignition timing and engine idle speed control. Input to the control unit is provided by an oxygen sensor, coolant temperature sensor, knock sensor, hot film air mass sensor and throttle position sensor. The PCM also receives information concerning engine rpm, road speed, transmission gear position, power steering and air conditioning.

On the 1996 and later 2.4L engines, and 1998 and later 2.2L engines, a sequential port fuel injection system (SFI) is used for more precise fuel control. With SFI, metered fuel is timed and injected sequentially through injectors into individual cylinder ports. Each cylinder receives one injection per working cycle (every two revolutions), just prior to the opening of the intake valve. The main difference between the two types of fuel injection systems is the manner in which fuel is injected. In the multiport system, all injectors work simultaneously, injecting half the fuel charge each engine revolution. The PCMs are different for SFI and MFI systems, but most other components are similar. The MFI system PCM has two injector drivers inside, one for two cylinders each and the SFI system PCM has four injector drive circuits, one for each cylinder.

Both systems use Bosch injectors, one at each intake port. The injectors are mounted on a fuel rail and are activated by a signal from the PCM. The injector is a solenoid-operated valve which remains open depending on the width of the electronic pulses (length of the signal) from the PCM; the longer the open time, the more fuel is injected. In this manner, the air/fuel mixture can be precisely controlled for maximum performance with minimum emissions.

Fuel is pumped from the tank by a high pressure fuel pump, located inside the fuel tank. It is a positive displacement roller vane pump. The impeller serves as a vapor separator and pre-charges the high pressure assembly. A pressure regulator maintains 28-36 psi in the fuel line to the injectors and the excess fuel is fed back to the tank.