COSWORTH VEGA
ELECTRONIC FUEL INJECTION FIELD GUIDE

ELECTRONIC CONTROL UNIT 

ENGINE SENSORS

The Engine Sensor Group is comprised of the following:


Manifold Air Pressure  

Throttle Position Switch

Coolant Temperature  

Air Temperature  

Speed Sensor

 

 

AIR INDUCTION 

The Air Intake Control  is comprised of the following:


Fast Idle Valve (FIV)

Air Solenoid Valve

Curb Idle Adjustment

FUEL DELIVERY 

The Fuel Deliver Subsystem  is comprised of the following:


Fuel Pump

Fuel Filter

Fuel Pressure Regulator

Injection Valves
(four in all)

How It Works

How It Works

How It Works


The sensors are electrically connected to the Electronic Control Unit and all operate independent of each other.

Each sensor transmits a signal to the ECU, relating a specific engine operating condition.

The ECU analyzes all the signals and transmits the appropriate timed commands to the injection valves.

The air-handling subsystem consists of the throttle body, intake manifold, fast idle valve, and air solenoid valve. 

Air required for combustion, enters the throttle body and is distributed to each cylinder through the intake manifold. The throttle valves within the throttle body, which control the primary air flow, are actuated by linkage connected to the accelerator.

 


Fuel is supplied to the cylinders through the injection valves which are mounted on top of the intake manifold.

Fuel is supplied to the injectors through a combination of a low pressure intank pump and a high pressure external mounted fuel pump.

Fuel pressure is controlled by a firewall mounted fuel pressure regulator.

Fuel filtration is accomplished by a frame mounted replaceable filter.

 

What They Are

What They Are

What They Are

Manifold Air Pressure (MAP) Sensor

(Click Here for a location and picture)

The Manifold Air Pressure Sensor monitors the changes in intake manifold vacuum which result from engine load variations. These pressure changes are relayed to the electronic control unit in the form of electrical signals.

The sensor also indicates the changes in atmospheric pressure due to changes in altitude.

The manifold air pressure sensor is mounted to the firewall of the engine compartment on the passenger side. A rubber vacuum hose connects it to the throttle body. A wiring harness provides the electrical connection with the electronic control unit.

(A wonderful site devoted to the MAP (MPS) theory of operation) 

Throttle Position Switch

(Click Here for a location and picture)

The Throttle Position Switch is mounted to the throttle body, throttle valve shaft. Movement of the accelerator causes the throttle shaft to rotate (opening or closing the throttle blades). The switch senses the shaft movement and position (closed throttle, wide open throttle, or any position in between), and transmits a pulsed electrical signal to the electronic control unit. The electronic control unit monitors the pulse rate (throttle position) to aid in determining the fuel requirement for the particular situation (idle, acceleration, etc.) The TPS also triggers the double injection mode.

Coolant Temperature Sensor

(Click Here for a location and picture)

 The Coolant Temperature Sensor contains a temperature sensitive electronic circuit in a brass housing. The sensor is in contact with the engine coolant fluid, constantly monitoring the temperature changes. The strength of the electrical signal received by the electronic control unit, indicates the temperature of the coolant fluid. The sensor is located in the engine coolant fluid thermostat housing.

Air Temperature Sensor

(Click Here for a location and picture)

The Air Temperature Sensor is similar to the coolant temperature sensor in configuration and operation and contains the same electronic temperature sensing circuit. The air temperature sensor is installed on the underside of the intake manifold and monitors the manifold air temperature which is a factor in air density measurement. The engine air/fuel ratio is maintained constant even though the engine air density varies.

 

Speed Sensor

(Click Here for a location and picture)

The Speed Sensor is a two piece device that monitors and transmits the engine speed (rpm) to the electronic control unit. The device consists of two reed switches in a plastic housing located on the rear of the distributor drive housing, and a rotor with a magnet which is installed on the distributor drive shaft. As the distributor drive shaft rotates, the speed sensor magnetic rotor passes the reed switches, closing and opening the metal contacts within, producing a signal. This signal, which indicates the engine speed, is transmitted to the Electronic Control Unit, through the engine harness.

 

Fast Idle Valve


(Click Here for a location and picture)

The Fast Idle Valve, which provides supplementary air during cold starts and engine warm-up, contains an air filter, spring and plunger, and a thermal sensitive element. The unit is mounted in the engine block under the intake manifold. An air hose connects it to the underside of the intake manifold. The valve, which is in contact with the engine coolant, senses the rising temperature of the engine. The internal thermal element expands in direct proportion to the rising engine temperature, reducing air flow. When the engine coolant reaches approximately 140 0F, the valve is fully closed and the engine attains a normal idle speed.

 

Air Solenoid Valve

(Click Here for a location and picture)

The Air Solenoid Valve is an electromechanical valve that aids in the control of engine speed during cold starting and engine warm-up. The unit is mounted to the firewall on the passenger side of the engine compartment and is controlled by the Electronic Control Unit. The valve bypasses the throttle body to provide additional air to the manifold when required.

The fast idle valve and air solenoid valve are active only during cold start and engine warm-up operation.

An idle by-pass air passage is a part of the throttle body that allows a controllable amount of air to by-pass the throttle valves during engine idling.

 

Fuel Pump


(Click Here for a location and picture)

The Fuel Pump is a constant-displacement, roller-vane type pump, driven by a wet brush 12 volt direct current motor. The pump incorporates a check valve to prevent back-flow from the high pressure side. An internal relief valve provides overpressure protection by opening at an excessive pressure. The pump has a flow rate of 33 gallons per hour under normal operating conditions. The pump is mounted forward of the fuel tank, under the vehicle, forward of the right rear wheel.

Fuel Filter

(Click Here for a location and picture)

The Fuel Filter consists of a casing with internal relief valve and filter element. The relief valve opens to bypass fuel from the filter element to ensure fuel flow in the event-that contamination trapped by the filter element restricts or prevents flow. The fuel filter is a throwaway type and should be replaced at prescribed intervals. The filter is mounted to the vehicle frame in the engine compartment.

Fuel Pressure Regulator

(Click Here for a location and picture)

The Fuel Pressure Regulator contains an air chamber and a fuel chamber separated by a diaphragm. The air chamber is connected by a rubber hose to the throttle body assembly. The pressure in this chamber is identical to the pressure of the intake manifold. The changing manifold pressure controls the action of the diaphragm valve, opening or closing an orifice in the fuel chamber. (Excess fuel is returned to the fuel tank.) This regulator, being connected to the fuel rail and intake manifold, maintains a constant pressure drop of 39 psi across the injection valves.

The fuel pressure regulator is mounted on the firewall of the engine compartment on the passenger side.

Injection Valve

(Click Here for a location and picture)

The Injection Valve is a solenoid operated needle valve that meters fuel to each cylinder. Based upon a pulsed signal from the electronic control unit, the valve opens for the proper time interval to deliver the exact amount of fuel required. When energized, the valve sprays the fuel in fine droplets. When de-energized, it acts as an effective seal, preventing fuel flow to the engine. Handling of the injection valve requires special care to avoid possible damage to the metering tip. The injection valves are located on the intake manifold above each cylinder.

Arguably fuel delivery begins with the engine speed sensor, then the ECU relay that is triggered on when engine rotation is sensed and cut off when engine rotation ceases.

The ECU is also involved in determining the length of time each injector is open.