Conventional EFI-diesel

Common-rail EFI-diesel

4. Comparison of the target injection timing and the actual injection timing

As with the convention EFI-diesel, the basic injection timing of the common- rail EFI-diesel is determined through the engine speed and the accelerator pedal opening angle, and by adding a correction value based on the water temperature and the intake air pressure (volume). The ECU sends injection signals to the EDU and advances or retards the timing to adjust the injection starting timing.

Starting Control

Injection Volume Control During Starting

The starting injection volume is determined by adjusting the basic injection volume in accordance with the starter ON signals (ON time) and coolant temperature sensor signals. When the engine is cold, the coolant temperature will be lower and the injection volume will be greater. To determine the starting injection timing is corrected in accordance with the starter signals, water temperature and engine speed. When the water temperature is low, if the engine speed is high, the injection timing is advanced.

Injection Rate Control

Split Injection

A radial plunger type pump performs split injection (two-time injection) when starting the engine at an extremely low temperature (or under -10 degrees) to improve startability and reduce the generation to white and black smoke.

Pilot Injection

The common-rail EFI-diesel uses pilot injection. In the pilot injection system, a small amount of fuel is initially injected before the main injection. When the main injection starts, the fuel that has been injected in advance is already ignited, enabling the fuel of the main injection to ignite smoothly.

Idle Speed Control

Based on the signals from the sensors, the ECU calculates the target speed in accordance with the driving conditions. The ECU then compares the target value with the (engine speed) signal from the engine speed sensor and controls the actuators(SPV/injector) to regulate the injection volume in order to correct the idle speed. The ECU effects idle-up control (in order to improve the engine’s warm-up performance) during fast idle when the engine is cold, or during air conditioner/power heater operations. Also, in order to prevent fluctuations in idle speed caused by a reduction in engine load that occurs when the A/C switch is turned off, the volume is automatically corrected before the engine speed fluctuates.

Idle Vibration Reduction Control

This control detects the fluctuations in the engine speed during idle caused by the variances in the injection pump or nozzles, and corrects the injection volume for each cylinder. Consequently, idle vibration and noise are reduced.

The ECU performs the following functions to determine the injection timing:

Conventional EFI-diesel

1. Determination of the target injection timing

2. Detection of the actual injection timing

3. Comparison of the target injection timing and the

actual injection timing

Common-rail EFI-diesel

4. Comparison of the target injection timing and the actual injection timing

Conventional EFI-diesel

1. Determination of the target injection timing

The target injection timing is determined by calculating the basic injection timing through the engine speed and the accelerator pedal opening angle, and by adding a correction value based on the water temperature, intake air pressure, and the intake air temperature.

Conventional EFI-diesel

1. Determination of the target injection timing

Conventional EFI-diesel

2. Detection of the actual injection timing

The detection of the actual injection timing is performed through a calculation based on the engine speed and crankshaft position signals. As with injection volume control, the variances that occur in injection timing control between pumps are corrected through the use of a correction resistor or a correction ROM.

REFERENCE

Injection Timing Detection

Conventional EFI-diesel

The cam plate and the rotor (which generates the NE signal of the engine speed sensor) rotate in unison. Therefore, the ECU is able to detect the timing when the plunger moves and an actual injection takes place by way of the position of the NE signal.

To address the phase discrepancy that occurs between the actual injection timing and the NE signal due to the individual variances of the pumps, a correction resister is used to correct and recognize it as the standard position. Compare the NE signal and the TDC signal of the crankshaft angle sensor and calculates the injection timinng in relation to the engine crankshaft angle as being the actual injection timing.

Conventional EFI-diesel

3. Comparison of the target injection timing and the actual injection timing

The ECU compares the target injection

timing and the actual injection

timing and sends timing advance and

timing retard signals to the timing

control valve so that the actual injection

timing and the target injection

timing match.

The ECU performs the following three functions to determine the injection volume:

1. Calculation of basic injection volume

2. Calculation of maximum injection volume

3. Comparison of basic injection volume and maximum injection volume

1. Calculation of basic injection volume

The calculation of the basic injection volume is made based on the signals of the engine speed and the amount of pedal effort applied to the accelerator pedal.

2. Calculation of maximum injection

volume

The calculation of the maximum injection volume is made based on the signals from the engine speed sensor (NE sensor), water temperature sensor, intake air temperature sensor, fuel temperature sensor, and turbo pressure. In the common-rail type, the signals from the fuel pressure sensor are also used.

Injection Volume Correction

Intake air pressure correction

The injection volume is corrected in accordance with the intake air pressure (volume).

Intake air temperature correction

The density of the intake air (air volume) varies in accordande with the temperature of the intake air. (Low intake air temperature →Injection volume increase correction)

Fuel temperature correction

High fuel temperature →Injection volume increase correction

Cold engine correction

Low water temperature →Injection volume increase correction

Fuel pressure correction

In a common-rail type diesel, the changes in the fuel pressure in the common- rail are detected based on the signals from the fuel pressure sensor. If the fuel pressure is lower than the target pressure, the length of time the injector nozzles remain open is extended.

Calculation of maximum injection volume

The ECU compares the calculated basic injection volume and the maximum injection volume and determines the smaller one to be the injection volume. Accelerator 60 % constant speed driving Accelerator 100 % sudden acceleration

3. Comparison of basic injection volume and maximum injection volume

The difference in the actual injection volume in the conventional EFI-diesel created by the mechanical variances that occur from pump to pump are corrected.

REFERENCE

About the correction ROM :

Authorized workshops such as pump service shops use special tools to measure the pumps to replace the correction ROMs or to make corrective adjustments.

Other types of corrections:

In addition to the injection volume that has been determined here, fuel temperature correction is also made on some vehicle models. If the fuel temperature is high, the actual injection volume is lower (due to the low density) than the instructed value. Therefore, the instructed value must be increased.

4. Acceleration enrichment
The air-fuel ratio becomes lean, especially during the start of acceleration because a fuel supply lag tends to occur during acceleration against the rapid change of the amount of the intake air when the accelerator pedal is depressed. For this reason, the injection duration is lengthened to increase the fuel injection volume against the intake air to prevent the air-fuel mixture from becoming lean. The acceleration is determined by the speed of the change in the throttle valve opening angle. The correction during acceleration increases greatly during the start of acceleration and is gradually reduced thereafter until the increase has ended. In addition, the more rapid the acceleration is, the larger the fuel injection volume increase.
5. Fuel cut-off
During deceleration, injection operation is stopped according to the deceleration condition in order to reduce the harmful exhaust gases and improve the engine braking effect. Then the fuel cut-off control is activated to cut-off the fuel injection. The state of deceleration is determined from the throttle valve opening and the engine speed. When the throttle valve is closed and the engine speed is high, it is determined that the vehicle is decelerating.
Fuel cut-off control
The fuel cut-off control stops the fuel injection when the engine speed is higher than a determined speed and the throttle valve is closed. Fuel injection will resume when the engine speed slows to a determined speed or the throttle valve is opened. The fuel cut-off engine speed and fuel injection resumption engine speed will increase when the coolant temperature is low. In addition, the fuel cut-off engine speed and fuel injection resumption engine speed are increased when the air conditioner switch is on to prevent the engine speed from falling and an engine from stalling. There are also some engine models in which these engine speeds drop during braking (i.e., when the stop light switch is on).
6. Power enrichment
As there is a large amount of the intake air at heavy loads, such as when climbing a steep hill, it is difficult to sufficiently mix the injected fuel with the intake air. And all of the intake air is not used during combustion, causing some to remain. Therefore, more fuel than for the theoretical air-fuel ratio is injected to use all of the intake air in combustion to increase power. Heavy loads are determined from the throttle position sensor opening, engine speed, and intake air mass (VG or PIM). The greater the intake air mass (VG or PIM) or the higher the engine speed is, the ratio of the increased amount becomes larger. In addition, the amount is further increased when the throttle valve opening angle becomes a certain value or more. The correction of the increased amount is from approx. 10% to 30%.
7. Intake air temperature correction
The air density changes depending on the air temperature. For this reason, a correction must be made to increase or decrease the fuel volume in accordance with the intake air temperature to optimize the mixture ratio required for the current engine conditions. The intake air temperature is detected by the intake air temperature sensor. The engine ECU is set to a standard intake air temperature of 20 C   (68 F). The correction amount is determined when the temperature rises above or falls below this temperature. When the intake air temperature is low, the amount is increased because the air density is high. When at high temperature, the amount is decreased because the air density is low. The correction of the increased/decreased amount is approx. 10%.
HINT:
For hot-wire type air flow meters, the air flow meter itself outputs a corrective signal for the intake air temperature. Therefore, intake air temperature correction is not required.
8. Voltage correction
There is a slight delay between the time where the engine ECU sends an injection signal to the injector, and the time when the injector actually injects the fuel. If there is a severe drop in battery voltage, then this delay will be longer. This means that the time the injector injects the fuel is shorter than the time calculated by the engine ECU. Therefore, the ratio of air becomes higher (in other words, leaner) than the mixture ratio required by the engine. For this reason, the engine ECU adjusts this by making the injector injection duration longer in accordance with the battery voltage drop.

1. Start enrichment
The basic injection duration cannot be calculated from the amount of the intake air because the engine speed is low and the changes in the amount of the intake air are large at starting. For this reason, the fuel injection duration at starting is determined from the coolant temperature. The coolant temperature is detected by the water temperature sensor. The lower the water temperature is the fuel vaporization becomes worse. Therefore, the air-fuel mixture is made richer by lengthening the injection duration. The engine ECU determines that the engine is being started when the engine speed is 40rpm or less. In addition, when the engine speed suddenly falls below 40rpm due to a sudden increase of the load on the engine, a hysteresis is used to prevent the engine ECU from determining that an engine that has already been started is being started again unless the engine speed falls below 20rpm.
SERVICE HINT:
When there is a malfunction with the water temperature sensor, it can be considered as the worse startability.
REFERENCE:
To improve startability while the engine was cold, the old type of EFI had a cold start injector and cold start time switch in addition to the regular injector to increase the fuel volume at starting.

2. Warm-up enrichment
The amount of the fuel injection is increased because the fuel vaporization is poor during the cold engine. When the coolant temperature is low, the fuel injection duration is increased to make the air-fuel mixture richer in order to attain the drivability during the cold engine. The maximum correction is twice as long as normal temperature.
SERVICE HINT:
When there is a malfunction with the water temperature sensor, it can be considered as poor drivability.

3. Air-fuel ratio feedback correction (For most models)
When there are no major fluctuations in the engine load or engine speed, such as when idling or driving at constant speed after warming up, fuel (air-fuel mixture close to the theoretical air-fuel ratio) is supplied based on the amount of the intake air. The following corrections are activated when driving at a constant speed after warming up.
(1) Feedback control using the oxygen sensor (Air-fuel ratio feedback control)The engine ECU determines the basic injection duration to achieve the theoretical air-fuel ratio. However, a slight deviation from the theoretical air-fuel ratio occurs in accordance with the actual engine conditions, changes over time, and other conditions. Therefore, an oxygen sensor detects the oxygen concentration in the exhaust gas to determine if the current fuel injection duration becomes the theoretical airfuel ratio against the amount of the intake air. If the engine ECU determines from signals of the oxygen sensor that the air-fuel ratio is richer than the theoretical air-fuel ratio, it shortens the injection duration to make the air-fuel mixture leaner. Conversely, if it determines that the air-fuel ratio is lean, it will lengthen the injection duration to make the air-fuel mixture richer. The feedback control operates to maintain the average air-fuel ratio at the theoretical air-fuel ratio by repeatedly performing minor corrections. (This is called a closed-loopoperation.)
In order to prevent overheating of the catalyst and assure
good engine operation, air -furl ratio feedback does not
occur under the following conditions (open-loop operation):
During engine starting
During after-start enrichment
During power enrichment
When the coolant temperature is below a determined level
When fuel cut-off occurs
When the lean signal continues longer than a determined
time The center point (a) changes during the feedback control such as time passes. In this case, the center point is forced to be returned to the center. If it is not, it will cause the out of the correction range of the feedback control. This is called air-fuel ratio learned control or long fuel trim.
(2) Feedback control using the air-fuel ratio sensor (A/F sensor):
The output voltage of the oxygen sensor changes rapidly around the theoretical air-fuel ratio as shown in the illustration (upper). The A/F sensor data which the engine ECU attains is displayed in the hand-held tester. (When the air-fuel ration is lean, the voltage is high. Conversely, the voltage is low when rich.) As a result, the detection precision of the air-fuel ratio has been improved. If the current air-fuel ratio changes from the theoretical air-fuel ratio as shown in the illustration (below), the engine ECU continuously corrects the air-fuel ratio using the oxygen sensor signal. For the A/F sensor, however, the engine ECU corrects instantly by determining the amount of change from the theoretical air-fuel ratio.
(3) CO emission control correction for vehicles without an oxygen sensor or A/F sensorFor vehicles without an oxygen sensor or A/F sensor, a variable resistor can be used to adjust the CO concentration (%) during idling. Turning the resistor to the R side makes the concentration richer, and turning it to the L side makes it leaner. For vehicles equipped with an oxygen sensor or A/F sensor, however, CO adjustment is not required during idling because these vehicles are automatically adjusted to the proper air-fuel ratio using the sensor signal.

The engine ECU changes the fuel injection volume by changing the injector injection duration. The actual fuel injection duration is determined by the following two items.
1. The basic injection duration is determined by the amount of the intake air and the engine speed.
2. The various corrective injection durations are determined by the signals from the various sensors. The injection duration that the engine ECU finally outputs into the injector is added various corrections to the basic injection duration. There are following corrections:
Start enrichment
Warm-up enrichment
Air-fuel ratio feedback correction (some models only)
Acceleration enrichment
Fuel cut-off
Power enrichment
Other corrections

The EFI system uses various sensors to detect the engine condition and vehicle running condition. And the engine ECU calculates at the optimum fuel injection volume, and causes the injectors to inject the fuel. The figure shows the basic EFI configuration.
Engine ECU
This calculates the optimum fuel injection duration based on the signals from the sensors.
Air flow meter or manifold pressure sensor
This detects the intake air mass or manifold pressure.
Crankshaft position sensor
This detects the crank angle and engine speed.
Camshaft position sensor
This detects the standard crank angle and the camshaft timing.
Water temperature sensor
This detects the coolant temperature.
Throttle position sensor
This detects the throttle valve opening angle.
Oxygen sensor
This detects the oxygen concentration in the exhaust gas.
Types of EFI
There are two types of EFI system classified by the amount of the intake air detection method.
1. L-EFI (Air-flow control type)
This type uses an air flow meter to detect the amount of the air flowing in the intake manifold. There are two types of detection methodsOne directly measures the intake air mass, and one makes corrections based on the air volume.
2. D-EFI (Manifold pressure controlctype)
This type measures the pressure in the intake manifold to detect the amount of the intake air using the intake air density.

EFI (Electronic Fuel Injection)System
The EFI system uses various sensors to detect the operating conditions of the engine and the vehicle. In accordance with the signals from these sensors, the ECU calculates the optimal fuel injection volume and operates the injectors in order to inject the proper volume of fuel. During ordinary driving, the engine ECU determines the fuel injection volume for achieving the theoretical air-fuel ratio, in order to ensure the proper power, fuel consumption, and exhaust emission levels simultaneously. At other times, such as during warm-up, acceleration, deceleration, or high-load driving conditions, the engine ECU detect those conditions with the various sensors and then corrects the fuel injection volume in order to ensure an optimal air-fuel mixture at all times. (1/1)
ESA (Electronic Spark Advance) System
The ESA system detects the conditions of the engine based on the signals provided by various sensors, and controls the spark plugs to generate sparks at the appropriate timing. Based on engine speed and engine load, the ESA precisely controls the ignition timing so that the engine can generate improve power, purify exhaust gases, and prevent knocking in an effective manner.
ISC (Idle Speed Control) System
The ISC system controls the idle speed so that it is always appropriate under varying conditions (warm-up, electrical load, etc.). To minimize fuel consumption and noise, an engine must operate at a speed that is as low as possible while maintaining a stable idle. Moreover, the idle speed must be increased to ensure the proper warm-up and drivability when the engine is cold or the air conditioner is being used.
Diagnostic System
The engine ECU contains a diagnostic system. The ECU constantly monitors the signals that are being input by various sensors. If it detects a malfunction with an input signal, the ECU records the malfunction in the form of DTCs (Diagnostic Trouble Codes) and illuminates the MIL (Malfunction Indicator Lamp). If necessary, the ECU can output the DTCs by blinking the MIL or displaying the DTCs or other data on the display panel of a handheld tester. The diagnostic functions that output the DTCs and datas of a malfunction on a hand-held tester are a highly advanced and complex form of electronics system. Because a diagnostic system must comply with the regulations of each country, its contents vary slightly by destination.

The TCV renders the LST inactive if the vehicle is operated with a cold engine (coolant temperature below 6C (14F)) or at high altitudes (where the atmospheric pressure is below 93 kPa (70mmHg)). The purpose of providing a TCV is to prevent misfiring. If the injection timing is allowed to keep advancing at conditions where misfiring occurs easily (cold engine or high altitude), misfiring is prevented. Then, white smoke is also prevented. The emission control ECU determines the conditions of the engine using signals from the water temperature sensor and the atmospheric pressure sensor.

Then, the emission control ECU outputs signals that cause the TCV to close the fuel passage of the LST, thus rendering the LST inactive. TCV on Before the engine has warmed up (coolant temperature below 6C (14F)) or when the vehicle is driven at high altitudes (where the atmospheric pressure is below 93 kPa (700mmHg)), the emission control ECU outputs signals that cause the TCV to turn on and close the fuel passage. Therefore, even if the accelerator pedal is released and the engine load decreases, the LST becomes inactivated and does not retard the injection timing.

The LST changes the fuel injection timing in accordance with the engine load, and obtain the characteristic of advancing. The fuel is released from the orifice on the governor sleeve via the governor shaft passage to the inlet side of the feed pump. Therefore, the pressure inside the pump housing is lowered to retard the injection timing. When the load on the engine increases (increased injection volume), the flyweights remain closed. The pressure inside the pump housing is not lowered because the orifice on the governor sleeve and the governor shaft passage are not aligned. On the contrary, when the load on the engine decreases (decreased injection volume), the flyweights open. The orifice on the governor sleeve and the governor shaft passage are aligned causing the pressure inside the pump housing to be reduced and the timing to be retarded.