General description and operation of the engine management system (Chevrolet Captiva 1)

The principle of operation of the ignition system

The ignition system does not use a conventional distributor and coil. It uses the output signals from the crankshaft position sensor to the ECM. The ECM determines the electronic timing adjustment and turns on the ignition coil.

This type of distributorless ignition system uses a "waste spark" distribution method. Each cylinder is paired with the opposite cylinder (1-4 or 2-3). Ignition occurs simultaneously in the cylinder rising in the compression stroke and in the cylinder falling in the exhaust stroke. The cylinder in the exhaust stroke requires very little of the available energy to ignite the spark plug. The remaining energy is provided to the spark plug in the cylinder in the compression stroke.



These systems use the EST signal from the ECM to control the ignition timing adjustment. The ECM uses the following information:

• Engine load (manifold pressure or vacuum).
• Atmospheric (barometric) pressure.
• Engine temperature.
• Intake air temperature.
• Crankshaft position.
• Engine speed (rpm)

Electronic ignition system coil

The electronic ignition coil supplies spark to two spark plugs simultaneously. The electronic ignition coil is not serviceable and is replaced as a single unit.

Crankshaft position sensor

The direct ignition system uses an inductive crankshaft position sensor. This sensor extends through its mount approximately 0.05 inch (1.3 mm) into the crankshaft pulse generator. The pulse generator is a special wheel mounted on the crankshaft or crankshaft pulley that has 58 slots, 57 of which are spaced 6 degrees apart. The last slot is wider and is used to generate a "timing pulse." As the crankshaft rotates, the slots in the pulse generator change the sensor's magnetic field, creating an inductive pulse. The long pulse of the 58th slot represents a specific orientation of the crankshaft and allows the ECM to continually determine the orientation of the crankshaft. The ECM uses this information to generate spark advance and fuel injection pulses, which it sends to the ignition coils and fuel injectors.

Camshaft Position Sensor

The camshaft position sensor sends a signal to the ECM controller. The ECM controller uses this signal as a "synchronization pulse" to open the fuel injectors in the required sequence. The ECM controller uses the camshaft position sensor signal to determine the position of piston No.1 during the operating cycle. This allows the ECM controller to calculate the correct sequential fuel injection mode. If the ECM controller detects an incorrect camshaft position sensor signal when the engine is running, then DTC P0341 is set. If the camshaft position sensor signal is lost while the engine is running, the fuel injection system will switch to sequential injection mode based on the last pulse, and the engine will continue to run. As long as the fault is present, the engine can be restarted. It will operate in the calculated sequential injection mode with a probability of the correct sequence of injectors of 1 to 6.

Operating principle of the idle speed controller

The operation of the idle air control valve is controlled by the primary idle setting of the throttle body and the idle air control valve.

The ECM controller uses an idle speed control valve to adjust the idle speed depending on the conditions. The ECM controller uses information from various input signals, such as coolant temperature, collector vacuum, etc., to effectively control the idle speed.

The principle of operation of the fuel supply system

The function of the fuel metering system is to supply the required amount of fuel to the engine in different operating modes. Fuel is supplied to the engine by individual fuel injectors mounted in the intake manifold next to each cylinder.

The main sensors that control the fuel supply are the manifold absolute pressure sensor, the control oxygen sensor (HO2S1), and the diagnostic oxygen sensor (HO2S2).

The manifold absolute pressure sensor measures the vacuum in the intake manifold. When fuel demand is high, the sensor reads low vacuum, such as at wide open throttle. The ECM uses this information to enrich the mixture, thereby increasing the injector run time and delivering the required amount of fuel. As the engine slows, the vacuum increases. The change in vacuum is detected by the MAP sensor and read by the ECM, which then reduces the injector run time due to the decreased fuel demand.

HO2S sensors

The HOS2 sensor is located in the exhaust manifold. The HO2S tells the ECM how much oxygen is in the exhaust, and the ECM changes the air/fuel ratio for the engine by controlling the fuel injectors. The best air/fuel ratio for reducing emissions is 14.7 to 1, which allows the catalytic converter to operate most efficiently. Because of the constant measurement and adjustment of the air/fuel ratio, the fuel injection system is called a "closed loop" system.



The ECM uses the output signals from various sensors to determine the amount of fuel required by the engine. Fuel is delivered under various conditions, called "modes".

Start mode

When the ignition switch is turned on, the ECM energizes the fuel pump relay for two seconds. The fuel pump increases fuel pressure. The ECM also monitors the engine coolant temperature (ECT) sensor and the throttle position (TP) sensor to determine the air/fuel ratio needed to start the engine. This ranges from 1.5 to 1 at -97°F (-36°C) coolant temperature to 14.7 to 1 at 201°F (94°C) coolant temperature. The ECM controls the amount of fuel delivered during cranking by varying the amount of time the fuel injector is on and off. This is done by "pulsing" the fuel injectors for a very short time.

Free flow mode

If the engine is flooded with excess fuel, it can be purged by fully depressing the accelerator pedal. The ECM will shut off the fuel supply completely, eliminating all signals to the injectors. The ECM will hold this output as long as the throttle remains wide open and the engine is running below about 400. If the throttle position drops below about 80 percent, the ECM will revert to the start mode.

Driving mode

The driving mode has two states called "open loop" and "closed loop".

Open circuit

If the engine has just started and is running above 400 RPM, the system goes into "open loop". In "open loop", the ECM ignores the signal from the HO2S and calculates the air/fuel ratio based on the input signals from the coolant temperature sensor and the manifold absolute pressure sensor. The sensor remains in "closed loop" until the following conditions occur:

• The HO2S sensor is giving an erratic output signal, indicating that it is too hot to operate properly.
• The coolant temperature sensor temperature is higher than the set value.
• A certain amount of time has passed since the engine was started.

Closed loop

Specific values for the above conditions vary from engine to engine and are stored in an electrically erasable programmable read-only memory (EEPROM). When these conditions are met, the system goes into "closed loop" mode. In "closed loop," the ECM calculates the air/fuel ratio (injector operating time) based on the oxygen sensor signal. This allows the air/fuel ratio to remain very close to 14.7 to 1.

Acceleration mode

The ECM responds to rapid changes in throttle position and air flow and delivers additional fuel.

Braking mode

The ECM responds to changes in throttle position and air flow and reduces fuel. If braking is very rapid, the ECM may cut off fuel supply for a short time.

Battery voltage correction mode

If the battery voltage is low, the ECM can compensate for the weak spark supplied by the ignition module in the following ways:

• Increases fuel injector pulse duration.
• Increase idle speed.
• Increase ignition delay time.

Fuel Shut-Off Mode

When the ignition is off, the fuel injectors do not supply fuel. This prevents the engine from running when the ignition is off. Fuel is also not supplied if there are no control pulses from the central power source. This prevents flooding.

Operating principle of the gasoline vapor recovery system

The gasoline vapor recovery system uses a carbon storage method. This method allows fuel vapors from the fuel tank to be directed to an activated carbon storage device (filter) to trap the fuel vapors when the vehicle is not running. When the engine is running, the fuel vapors are purged from the carbon element by the intake air and used in the normal combustion process.



Gasoline vapors from the fuel tank are directed to the pipe marked TANK. These vapors are adsorbed by carbon. The carbon filter is purged by the ECM when the engine has been running for a certain period of time. Air is supplied to the carbon filter and mixed with the vapors. The mixture is then supplied to the intake manifold.

The ECM grounds the EVAP canister solenoid valve. This valve is pulse width modulated (PWM) and cycles on and off several times per second. The EVAP canister purge cycle varies according to the operating mode determined by mass air flow, fuel trim, and intake air temperature.

Rough idle, engine stalling, poor handling may be caused by the following reasons:

• Faulty electromagnetic valve for purging the Emission Control System adsorber.
• Damaged carbon filter.
• The hoses are cracked, damaged, or not connected to the correct connections.

Adsorber of the gasoline vapor recovery system

The Evaporative Emissions Canister is an emission control device containing activated carbon granules. The Evaporative Emissions Canister is used to retain fuel vapors from the fuel tank. When certain conditions are met, the ECM activates the Evaporative Emissions Canister Purge Solenoid Valve, allowing fuel vapors to enter the engine cylinders and be burned.

The principle of operation of the forced crankcase ventilation system

The positive crankcase ventilation system is used to fully utilize the crankcase vapors. Fresh air is supplied to the crankcase from the air filter. The fresh air is mixed with the leaking gas, which then enters the intake manifold through a vacuum hose.

Inspect hoses and clamps regularly. Replace crankcase ventilation components if necessary.

A clogged or blocked PVC hose can cause the following conditions:

• Rough idle
• Engine stalling or low idle speed
• Oil leaks
• Oil in the air filter
• Sludge in the engine

A leaking PVC hose can cause the following conditions:

• Rough idle
• Engine stop
• High idle speed

Coolant temperature sensor

The engine coolant temperature (ECT) sensor is a thermistor (a resistor that changes resistance depending on temperature), installed in the engine coolant stream. Low coolant temperature causes high resistance (100,000 ohms at -40°F [-40°C]), while high temperature causes low resistance (70 ohms at 266°F [130°C]).

The ECM supplies 5 volts to the coolant temperature sensor through a resistor in the ECM and measures the change in signal level. The signal level is high when the engine is cold and low when the engine is hot. By measuring the change in signal level, the ECM can determine the coolant temperature. Coolant temperature affects most systems controlled by the ECM. A malfunction in the ECT sensor circuit can cause a DTC P0117 or P0118 to set. Remember that these DTCs indicate a malfunction in the ECT sensor circuit, so proper use of the chart will result in either a wiring repair or sensor replacement.

Throttle position sensor

The throttle position sensor is a potentiometer connected to the throttle body shaft. The throttle position sensor circuit consists of a 5-volt power wire and a ground wire from the ECM. The ECM calculates the throttle position by monitoring the voltage on this signal line. The throttle position sensor output changes with the accelerator pedal position, changing the opening angle of the throttle valve. When the throttle valve is closed, the throttle position sensor output is low, about 0.5 volts. As the throttle valve opens, the output increases, and at wide-open throttle, the output is about 5 volts.

The ECM can determine fuel delivery based on the throttle valve opening angle (at the driver's command). A broken or poorly connected throttle position sensor can cause intermittent fuel flashes from the injector and unstable idling, as the ECM controller assumes that the throttle is moving. A problem in any throttle position sensor circuit should set the diagnostic trouble code P0121 or P0122. After installing the DTC, the ECM controller will replace the default value for the throttle sensor, and the engine will return some power. The DTC P0121 results in a high idle speed.

Diagnostic oxygen sensors

Three-way catalytic converters are used to control the emission of hydrocarbons (HC), carbon monoxide, and nitrogen oxides (NOx). The catalyst inside the converters maintains a chemical reaction. This reaction oxidizes the HC and CO present in the exhaust gases and converts them into harmless water vapor and carbon dioxide. The catalytic converter also reduces NOx by converting it into nitrogen. The ECM monitors this process using the HO2S1 and HO2S2 sensors. These sensors provide a signal indicating the amount of oxygen in the exhaust gases entering and leaving the three-way converter. This reflects the ability of the converter to effectively convert the exhaust gases. If the catalytic converter is operating efficiently, the HO2S1 sensor signals will be more active than the HO2S2 sensor signals. The sensors that monitor the efficiency of the converter work in the same way as the sensors that control fuel delivery. The primary function of these sensors is to monitor the efficiency of the catalyst, but they also play a limited role in fuel management. If the sensor output shows an offset voltage above or below 450 mV for an extended period of time, the ECM will slightly adjust the fuel trim to ensure that the fuel delivery is correct for catalyst efficiency monitoring.

A problem with the HO2S1 sensor will set diagnostic trouble codes P0131 or P0132, depending on the special condition. A problem with the HO2S2 sensor signal will set diagnostic trouble codes P0137, P0138, or P0140, depending on the special condition.

A fault in the heated oxygen sensor (HO2S2) heater or its power or ground wire will cause a lower HO2S response signal. This may result in incorrect catalytic converter efficiency test results.

Exhaust gas recirculation valve

Exhaust gas recirculation is used on engines equipped with an automatic transmission to reduce NOx emissions (nitrogen oxides), caused by high combustion temperatures. The EGR valve is controlled by the ECM. The EGR valve allows a small amount of exhaust gas to flow into the intake manifold to reduce combustion temperatures. The amount of exhaust gas recirculated is controlled by changing the vacuum and exhaust back pressure. If too much exhaust gas is present, combustion does not occur. For this reason, only a small amount of exhaust gas is allowed to flow through this valve, especially at idle.

The exhaust gas recirculation valve is normally open in the following cases:

• The engine has warmed up.
• Above idle speed.

Results of incorrect operation

Excessive exhaust flow weakens combustion, causing the engine to run rough or stall. If exhaust flow is too high, the following conditions may occur at idle, while driving, or when the engine is cold:

• Engine stalls after cold start.
• The engine stops at idle speed after braking.
• The engine makes a popping noise while driving.
• Rough idle.

If the EGR valve is left open all the time, the engine may not idle properly. Too little or too much exhaust flow allows combustion temperatures to rise too high during acceleration and load. This can cause the following conditions:

• Detonation combustion (detonation)
• Engine overheating
• Toxicity Test Failure

Intake air temperature sensor

The intake air temperature sensor is a thermistor - a resistor that changes resistance depending on the temperature of the air entering the engine. Low temperatures cause high resistance (4500 ohms at -40°F [-40°C]), while high temperatures cause low resistance (70 ohms at 266°F [130°C]).

The ECM supplies 5 volts to the IAT sensor through a resistor in the ECM and measures the change in signal level to determine the intake air temperature. The signal level is high when the air in the manifold is cold and low when the air is hot. The ECM gets its intake air temperature information by measuring the voltage.

The intake air temperature sensor is also used to control ignition timing when the air in the manifold is cold.

A malfunction in the intake air temperature sensor circuit will set diagnostic trouble codes P0112 or P0113.

Throttle Actuator Control (TAC)

The Throttle Control System (TAC) is used to improve emissions, fuel economy, and overall handling characteristics. The Throttle Control System (TAC) eliminates the mechanical coupling between the accelerator pedal and the throttle. The throttle Control System (TAC) eliminates the need for an automatic speed control system and an electric motor for controlling the idle air supply. The following is a list of components of the Throttle Control System (TAC):

• The accelerator pedal assembly includes the following components:
• Accelerator pedal.
• Accelerator pedal position sensor (APP).
• Sensor 2 APP.
• The throttle body assembly includes the following components:
• Throttle Position (TP) Sensor 1.
• Throttle Position (TP) Sensor 2.
• Throttle actuator motor.
• Throttle valve.
• ECU controller.

The ECM monitors the driver's acceleration request using 2 APP sensors. APP sensor 1 has a voltage range of approximately 0.7-4.5 volts, changing as the accelerator pedal moves from the rest position to the full-travel position. APP sensor 2 has a voltage range of approximately 0.3-2.2 volts, changing as the accelerator pedal moves from the rest position to the full-travel position. The ECM processes this information along with other sensor inputs to command the throttle valve to a specific position.

The throttle valve is controlled by a DC motor called the throttle actuator motor. The ECM can move this motor forward or in reverse by controlling battery voltage and/or ground to two onboard drivers. The throttle valve is held in the 5.7° home position of the throttle position sensor (TPS) by a constant force return spring. When no current is supplied to the throttle actuator motor, this spring holds the throttle valve in the home position.

The ECM monitors the throttle angle using 2 TP sensors. The voltage range of TP sensor 1 changes from approximately 0.7 to 4.3 volts as the throttle valve moves from 0 percent to wide open throttle (WOT). The voltage range of TP sensor 2 changes from approximately 4.3 to 0.7 volts as the throttle valve moves from 0 percent to wide open throttle (WOT).

The ECM runs diagnostics that check the voltage levels of both APP sensors, both TP sensors, and the throttle actuator motor circuit. It also monitors the return speed of both return springs, which are housed inside the throttle body assembly. These diagnostics are run on different time scales based on whether the engine is running or stopped.

Each time the ignition is turned on, the ECM performs a quick test of the throttle return spring to ensure that the throttle valve can return to the 7 percent home position from the 0 percent position. This is to ensure that the throttle valve can be returned to the home position in the event of a motor actuator circuit failure.

Manifold Absolute Pressure Sensor

The manifold absolute pressure (MAP) sensor measures changes in manifold pressure due to changes in engine load and speed and converts them into an output signal.

When the throttle valve is closed, it produces a relatively low signal of absolute pressure in the manifold when moving by inertia. Absolute pressure is the opposite of discharge. When the manifold pressure is high, the discharge is low. The manifold absolute pressure sensor is also used to measure barometric pressure. It is performed as part of the calculations of the manifold absolute pressure sensor. When the ignition is switched on and the engine is switched off, the ECM controller reads the manifold pressure as a barometric pressure and adjusts the air / fuel ratio accordingly. Height compensation allows the system to maintain power at low toxicity levels. The barometric function is updated periodically while driving at a constant speed or when the throttle is fully open. In the event of a malfunction in the barometric part of the manifold absolute pressure sensor, the ECM controller sets the default value.

A fault in the manifold absolute pressure sensor circuit will set diagnostic trouble codes P0107 or P0108.

The following table shows the difference between absolute pressure and vacuum relative to the MAP sensor output signal, which is shown in the top row of both tables.

MAP

volt	4.9	4.4	3.8	3.3	2.7	2.2	1.7	1.1	0.6	0.3	0.3
kPa	100	90	80	70	60	50	40	30	20	10	0
in. Hg	29.6	26.6	23.7	20,7	17.7	14.8	11.8	8,9	5.9	2.9	0

VACUUM

volt	4.9	4.4	3.8	3.3	2.7	2.2	1.7	1.1	0.6	0.3	0.3
kPa	0	10	20	30	40	50	60	70	80	90	100
in. Hg	0	2.9	5.9	8,9	11.8	14.8	17..7	20,7	23.7	26.7	29.6

Electronic Engine Management System (EEMS) Controller

The ECM, located inside the passenger side kick panel, is the control center of the fuel injection system. It constantly monitors information from various sensors and controls the systems that affect the vehicle's operation. The ECM also performs diagnostic functions for the system. It can recognize problems in operation, alert the driver via a warning light (Check Engine), and also store diagnostic trouble codes that identify problem areas and help with repairs.

There are no repairable parts in the ECM. The settings are stored in the ECM in programmable read-only memory (EPROM).

The ECM supplies 5 or 12 volts to power the sensors or switches. This is done using resistors in the ECM that have such a high resistance that the test light does not light when connected to the circuit. In some cases, a regular commercial voltmeter will not give an accurate reading because their resistance is too low. You should use a digital voltmeter with an input resistance of 10 megaohms to get an accurate reading. The ECM controls output circuits such as the fuel injectors, idle air control valve, and A/C clutch relay by driving the ground circuit through transistors or a device called a "quad driver".

Fuel injector

The Multiport Fuel Injection (MFI) unit is a solenoid-controlled device from the ECM. It directs pressurized fuel to an individual cylinder. The ECM energizes the fuel injector or solenoid until the ball or needle valve is normally closed. This allows fuel to flow to the top of the injector, past the ball or needle valve, and through a recessed guide plate to the injector outlet.

The guide plate has six holes that control the flow of fuel and form a conical spray pattern of fine fuel on the injector nozzle. The fuel from the nozzle is directed to the inlet valve, where it is atomized and vaporized further before being fed into the combustion chamber. A partially open fuel injector will cause the fuel pressure to drop after the engine is stopped. Some engines also experience longer starting times. Running the engine with the ignition off may also be caused by the ability to supply fuel.

Knock sensor

The knock sensor detects abnormal engine detonation. The sensor is mounted in the engine block next to the cylinders. The sensor outputs an AC signal that increases with the force of the detonation. This signal is sent to the ECM controller. The ECM controller adjusts the ignition timing to reduce detonation.

[The article is based on data from the website: CHEVYMAN.RU]