INTRODUCTION
This article covers basic description and operation of engine performance-related systems and components. Read this article before diagnosing vehicles or systems with which you are not completely familiar.
ELECTRONIC CONTROL UNIT
The Electronic Control Unit (ECU) continually corrects air/fuel mixture, based on signals from oxygen sensor. The ECU sends signals to differential pressure regulator, located on the fuel distributor. See Fig.1 . See ENGINE CONTROL/FUEL SYSTEM APPLICATION and ECU LOCATION tables.
CIS-E and CIS-Motronic fuel injection systems perform basic air-measuring and fuel-metering in the mixture control unit. The mixture-control unit is actually a combination of two separate components. The airflow sensor and fuel distributor, deliver proportional amounts of pressurized fuel to the injectors. The fuel distributor has electronic input and output control devices to help accurately control the volume of fuel delivered under various operating conditions. The system consists of mixture control unit (airflow sensor and fuel distributor), control pressure (warm-up) regulator, auxiliary air regulator, cold start valve, thermo time switch, fuel injectors, fuel pump, filter, oxygen sensor, ECU, differential pressure regulator and catalytic converter.
The CIS-Motronic engine management system uses a single control unit for fuel injection, idle speed control, ignition, and emission controls. Basic fuel injection and idle control are similar in CIS-E and CIS-Motronic. The oxygen sensor in the CIS-Motronic system can adjust its range in response to changes in operating conditions.
ENGINE CONTROL/FUEL SYSTEM APPLICATION
| Application | Fuel System |
|---|---|
| Fox | CIS-E |
| Jetta GLi | CIS-Motronic |
ENGINE CONTROL/FUEL SYSTEM APPLICATION
ECU LOCATION
| Application | Location |
|---|---|
| CIS-E | Behind Right Side of Glove Box |
| CIS-Motronic | Under Engine Compartment Plenum On Driver's Side |
ECU LOCATION
Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the control unit. The second category covers OUTPUT SIGNALS, which are components controlled by the control unit.
INPUT DEVICES
Note. All vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input usage on a specific model, see WIRING DIAGRAMS article.
AIRFLOW SENSOR POTENTIOMETER
Airflow sensor potentiometer is connected to the air sensor plate actuating lever. It returns a voltage signal to the ECU based on throttle valve position. The ECU uses this signal to calculate fuel mixture adjustments.
COOLANT TEMPERATURE SENSOR
Feeds a return signal to ECU for fuel control.
HEATED/EXHAUST GAS OXYGEN SENSOR
Located in exhaust manifold, the heated/exhaust gas oxygen sensor measures amount of unburned oxygen in exhaust. If oxygen is low (rich mixture), higher voltage will be generated by sensor. If oxygen is high (lean mixture), lower voltage will be generated. Voltage signal from oxygen sensor is sent to ECU which controls fuel mixture through the differential pressure regulator. The heated portion is used to rapidly warm the oxygen sensor for more effective emission controls.
HALL EFFECT SENSOR
See IGNITION SYSTEM in this article.
IDLE/FULL THROTTLE (FUEL) ENRICHMENT SWITCH
With the throttle closed the idle/ full throttle switch supplies the ECU inputs for
- Idle Stabilizer
- Deceleration Fuel Shut-Off
- ECU
The Idle/full throttle enrichment switch supplies the ECU with information to increase fuel during full throttle operation and cut fuel during deceleration.
OUTPUT SIGNALS
Note. For theory and operation on each output component, refer to the system indicated in brackets, to the right of each component.
- Auxiliary Air Regulator (Idle Speed)
- Cold Start Valve (Fuel Control)
- Differential Pressure Regulator (Fuel Control)
- Fuel Injectors (Fuel Control)
FUEL PUMP
Main pump is located to rear of vehicle on frame crossmember. A transfer pump is located inside fuel tank. Main fuel pump assembly, has a pressure damper at the suction end. Fuel pumps are activated during start-up and when engine is running.
The main electric fuel pump provides fuel system pressure of 68-80 psi (4.7-5.6 kg/cm 2 ). The transfer pump pulls fuel from the tank and pushes it to the main fuel pump. Fuel pump control relay prevents continued operation of fuel pumps if engine stalls. To aid in starting, a fuel accumulator and check valves in the pump and at fuel filter maintain line pressure when engine is not running.
FUEL PRESSURE REGULATOR
System pressure is created by the fuel pump and controlled by fuel pressure regulator. The fuel pressure regulator returns fuel to fuel tank when system pressure exceeds need. System is self-adjusting.
FUEL PUMP RELAY
Fuel pump relay switches off fuel pumps when ignition signal is cut off.
COLD START VALVE
Cold start valve, mounted on intake manifold, sprays fuel to enrichen mixture during starting so engine will start easily. The cold start valve is powered through starter circuits and grounded through thermo time switch. It operates for 3-10 seconds when cold engine is being cranked only.
DIFFERENTIAL PRESSURE REGULATOR (DPR)
The DPR, mounted on side of fuel distributor, is an electrically operated plate valve. Combined with fixed outlet orifice, the DPR governs pressure in lower chamber. Pressure change in lower chamber moves diaphragm and adjusts fuel volume flow to injectors. Actuating signal comes from ECU and ranges from -60 to +110 mA, depending upon engine operating conditions.
FUEL DISTRIBUTOR
The fuel distributor mechanically controls fuel to the injectors. Air being drawn over the sensor plate raises or lowers the fuel distributor control plunger. Differential pressure is the difference between upper (injector supply) and lower (fuel return) chambers of the fuel distributor, controlled by the differential pressure regulator. This controls the pressure differential at the fuel distributor metering ports, which determines the fuel flow to the injectors and air/fuel mixture.
FUEL INJECTORS
Fuel injectors in CIS-E system open at a preset pressure. Fuel is always present in lines between fuel distributor and injectors to ensure good starting. As pressure from fuel distributor increases (when engine is started), valves open and spray constantly. Amount of fuel injected will be determined by position of control plunger in fuel distributor and amount of voltage to differential pressure regulator.
THERMO TIME SWITCH
Energizes the cold start valve to provide cold start enrichment when engine temperature is below 86°F (30°C).
AUXILIARY AIR REGULATOR
Component is located in throttle valve by-pass hose. During cold start operation, auxiliary air regulator provides additional air to engine to increase idle speed. It allows intake air to by-pass throttle plates which are closed at idle. Heating coil in regulator is connected to fuel pump circuit. As coil warms up, air passage gradually closes. When energized, it will route air around throttle valve to increase idle speed.
IDLE AIR STABILIZER VALVE
The electronic idle air stabilizer valve adjusts the amount of air bypassing the throttle valve to control engine idle speed. the stabilizer valve receives signals from ECU based on engine RPM, idle switch and other inputs. On CIS-E systems the idle air stabilizer system is limited to measuring the duty cycle and is adjustable. On CIS-Motronic no adjustment is possible, the idle air screw should be turned in all the way.
IDLE SPEED BOOST VALVE I
Component is located in throttle valve by-pass hose. Idle speed boost valve will be energized when any electrical power consumer is turned on. When idle speed boost valve is energized, air will be routed around throttle valve to increase idle speed.
IDLE SPEED BOOST VALVE II (A/C MODELS)
Component is located in throttle valve by-pass hose. Idle speed boost valve will be energized when the A/C compressor is turned on. When idle speed boost valve is energized, air will be routed around throttle valve to increase idle speed.
ELECTRONIC IGNITION SYSTEM
The Hall Effect sending unit in the distributor uses a shutter window wheel mounted on the distributor shaft. The shutter blades pass in and out of the air gap of the hall effect sender resulting in signal pulses. There is one shutter window for each engine cylinder.
Signals from distributor hall sender are sent to the ignition control unit. The ignition control unit sends a switching voltage signal to the ignition coil primary circuit to discharge secondary spark voltage.
IGNITION TIMING ADVANCE CONTROL
Conventional vacuum and centrifugal advance is used.
EVAPORATIVE EMISSIONS SYSTEMS
As fuel expands in fuel tank, vapor is forced out of the fuel tank through an upper vent port. Vapor flows up through a gravity valve and into an expansion tank where liquid fuel condenses and returns to fuel tank as temperature drops. Fuel vapor then flows from an upper vent port of expansion tank, through a control valve, and into the charcoal canister.
When the engine is running at speeds faster that idle. A vacuum signal opens control valve. Canister vapor is drawn from canister through control valve and into intake manifold for burning.
MISCELLANEOUS CONTROLS
Note. Although not considered true Engine Performance related systems, some controlled devices may affect driveability if they malfunction.
COOLING FAN MOTOR
Note. If detonation is a problem with a vehicle, it is possible the cooling fan is not coming on at proper temperature and should be considered as a possible cause.
The cooling fan is either a one or two speed motor. If vehicle is equipped with single speed motor the fan comes on at 198-207°F (92-97°C) and off at 183-196°F (84-91°C). If equipped with a two speed motor. The first speed of cooling fan should come on at 196°F (91°C) and go off at 178°F (81°C). Second speed comes on at 203-212°F (95-100°C) and off at 189°F (87°C).