Ford Escort/Tracer 1991-1999 Repair Guide

Description and Operation


There are two types of gasoline fuel injection systems used on the Ford Escort and Mercury Tracer:

Multi-port Fuel Injection (MFI)
Sequential Fuel Injection (SFI)


Ford Motor Co. also refers to this system as Electronic Fuel Injection (EFI).

The Multi-port Fuel Injection (MFI) system is classified as a multi-point, pulse time, mass airflow fuel injection system. Fuel is metered into the intake air stream in accordance with engine demand through four injectors mounted on a tuned intake manifold.

An air induction system and a fuel injection system work in conjunction with an electronic engine control system. The electronic engine control system consists of various sensors, switches and a Powertrain Control Module (PCM). The PCM then uses the input from the switches and sensors to control the various output devices. The output devices are:

Fuel injectors
Idle Air Control (IAC) valve
Evaporative Emission Canister Purge (CANP) valve
High Speed Inlet Air (HILA) shutter valve actuator
Fuel pressure regulator
A/C relay
Ignition Control Module (ICM)

By controlling these outputs, the PCM can meet the different operation and driveability needs of the engine.


This system was called "SEFI" in 1991 and 1992. The name was shortened to "SFI" by Ford Motor Co. beginning in 1993. The later name is used in this guide to simplify understanding. By either designation, the Sequential Fuel Injection system is essentially the same for 1991-99 vehicles.

The Sequential Fuel Injection (SFI) system, used on SFI engines, is classified as a multi-point, pulse time fuel injection system. Fuel is metered into each intake port by a fuel injector in sequence with the engine firing order.

An on-board Powertrain Control Module (PCM) accepts electronic input signals from various engine sensors to compute the required fuel flow rate necessary to maintain a pre-determined air/fuel ratio throughout all engine operating ranges.

The PCM also determines and compensates for the age of the vehicle. This system will automatically sense and compensate for changes in altitude, and will also permit push-starting of the vehicle (manual transaxle only), if necessary.

The fuel charging manifold assembly (fuel rail) incorporates four electrically actuated fuel injectors directly above each of the engine's intake ports. Each injector, when energized, sprays a metered quantity of fuel into the intake air stream.

The system pressure is controlled by a pressure regulator connected in series with the fuel injectors and positioned downstream from them. Excess fuel, not required by the engine, passes through the regulator and returns to the fuel tank through a fuel return line.

The SFI system can be broken down into four categories:

Fuel delivery
Air induction

The fuel system is equipped with an in-tank mounted fuel pump.