Mazda Trucks 1987-1993 Repair Guide

General Information


The fuel injection system supplies the fuel necessary for combustion to the injectors at a constant pressure. Fuel is metered and injected into the intake manifold according to the injection control signals from the Engine Control Unit (ECU) or Engine Control Assembly (ECA). Most fuel injection systems consist of the following components: a fuel filter, distribution pipe, pulsation dampener, pressure regulator, injectors, fuel pump switch located in the airflow meter or mass airflow sensor for Navajo and the electric fuel pump usually located in the fuel tank in order to keep operating noise to a minimum.

The ECU or ECA, through various input sensors, monitors battery voltage, engine rpm, amount of air intake, cranking signals, intake temperature, coolant temperature, oxygen concentration in the exhaust gases, throttle opening, atmospheric or barometric pressure, gearshift position, clutch engagement, braking, power steering operation and air conditioner compressor operation.

The ECU or ECA controls operation of the fuel injection system, idle up system, fuel evaporation system and ignition timing. The control assembly has a built in fail safe mechanism. If a fault occurs while driving, the control assembly will substitute pre-programmed values. Driving performance will be affected but the vehicle will still, in most cases be drivable.


Safety is the most important factor when performing not only fuel system maintenance but any type of maintenance. Failure to conduct maintenance and repairs in a safe manner may result in serious personal injury or death. Maintenance and testing of the vehicle's fuel system components can be accomplished safely and effectively by adhering to the following rules and guidelines.

To avoid the possibility of fire and personal injury, always disconnect the negative battery cable unless the repair or test procedure requires that battery voltage be applied.
Always relieve the fuel system pressure prior to disconnecting any fuel system component (injector, fuel rail, pressure regulator, etc.), fitting or fuel line connection. Exercise extreme caution whenever relieving fuel system pressure to avoid exposing skin, face and eyes to fuel spray. Please be advised that fuel under pressure may penetrate the skin or any part of the body that it contacts.
Always place a shop towel or cloth around the fitting or connection prior to loosening to absorb any excess fuel due to spillage. Ensure that all fuel spillage (should it occur) is quickly removed from engine surfaces. Ensure that all fuel soaked cloths or towels are deposited into a suitable waste container.
Always keep a dry chemical (Class B) fire extinguisher near the work area.
Do not allow fuel spray or fuel vapors to come into contact with a spark or open flame.
Always use a backup wrench when loosening and tightening fuel line connection fittings. This will prevent unnecessary stress and torsion to fuel line piping. Always follow the proper torque specifications.
Always replace worn fuel fitting O-rings with new. Do not substitute fuel hose or equivalent where fuel pipe is installed.