Fuel Injection Control System
FUEL INJECTION CONTROL SYSTEMThe Electronic Fuel Injection system in this vehicle supplies the combustion chambers with air/fuel mixture of optimized ratio under widely varying driving conditions.
It uses the sequential multiport fuel injection system which injects fuel into each intake port of the cylinder head.
In this system, ECM (PCM) controls the time (amount) and timing of the fuel injection from the fuel injector into the cylinder head intake port according to the signals from the various sensors so that suitable air/fuel mixture is supplied to the engine in each driving condition.
INJECTION TIMING
There are 2 types of injection timing. One is "synchronous injection" in which injection takes place at the same crank angle all the time and the other is "asynchronous injection" in which the fuel is injected according to sensor signals other than the CMP sensor signal.
Synchronous Injection
At start
All 4 injectors inject fuel simultaneously and synchronously at every BTDC 75 ° signal (J20) or BTDC 82 ° (G16) of CMP sensor.
Other than at start
When each cylinder is in the exhaust stroke, fuel injection occurs only from the injector of that cylinder.
ECM (PCM) detects the compression stroke of No.1 cylinder through the CMP sensor signal and on the basis of this, it controls sequential fuel injection from each injector of Nos. 1, 3, 4 and 2 cylinder in that order.
Asynchronous Injection
Whenever a change in throttle valve opening exceeds its specified value, fuel is injected in the cylinder which is in the intake stroke and that in the exhaust stroke simultaneously in addition to the above synchronous injection.
INJECTION TIME (AMOUNT OF INJECTION)
The factors to determine the injection time are the basic injection time which is calculated on the basis of the engine speed and the amount of the intake air and various compensations which are determined according to the signals from various sensors that detect the state of the engine and driving conditions.
Enriching Compensation While Engine Starting
In order to improve starting performance, enriching compensation at start is carried out.
Enriching Compensation After Engine Start
For a certain time after the engine is started, air/fuel mixture enriching compensation is made so as to stabilize the engine speed. The amount of compensation varies depending on the engine coolant temperature and it is the largest immediately after the engine start and after that, it reduces gradually.
Enriching Compensation While Warming Up
When the engine is cold, enriching compensation is made to ensure good driveability till the engine coolant temperature reaches the specified level. The amount to enrich the air/fuel mixture is decreased as the temperature rises.
Power Enriching Compensation
To ensure smooth acceleration and good driveability under the high load driving condition, enriching compensation is carried out when the throttle valve opening is larger than specification.
Enriching Compensation When Accelerating
When the accelerator pedal is depressed, the enriching compensation takes place to obtain smooth acceleration performance. The amount of increase for compensation depends on the engine coolant temperature.
Battery Voltage Compensation
A power voltage drop delays the mechanical operation of the injector. Then the actual injection time becomes shorter for the time that electricity is supplied to the injector. To compensate this, the electricity supply time is made longer when the voltage is lower.
Base Air/Fuel Ratio Compensation
The air/fuel ratio may vary due to such factors as variation in each engine itself and aging. To compensate such variation, feed back compensation is used and base air/fuel mixture ratio is adjusted to a proper level for feed back compensation.
Fuel Cut
Fuel injection stops (with operation of the injector prevented) when decelerating, so that unburned gas will not flow into the catalyst as it will cause damage to the catalyst and change the exhaust gas for the worse. Fuel injection starts again when above conditions for fuel recovery are fulfilled.
The fuel injection also stops when the engine speed exceeds 6,800 r/min to prevent over-run which affects the engine adversely and it starts again when the engine speed reduces to less than 6,500 r/min.
CLOSED LOOP SYSTEM (AIR/FUEL RATIO FEED BACK COMPENSATION)
It is necessary to keep the air/fuel mixture close to the theoretical air/fuel ratio (14.7) to obtain efficient performance of the three way catalytic converter and high clarification rate of CO, HC and NOx in the exhaust gas. For that purpose, ECM (PCM) operates as follows. It first compares the signals from the heated oxygen sensor 1 and 2 with a specified reference voltage and if the signal is higher, it detects that the air/fuel ratio is richer than the theoretical air/fuel ratio and reduces fuel.
On the other hand, if the signal is lower, it detects that the air/fuel ratio is leaner and increases fuel. By repeating these operations, it adjusts the air/fuel ratio closer to the theoretical air/fuel ratio.
1. When oxygen concentration in the exhaust gas is low, that is, when the air/fuel ratio is smaller than the theoretical air/fuel ratio (fuel is richer), electromotive force of the oxygen sensor increases and a rich signal is sent to ECM (PCM).
2. Upon receipt of the rich signal, ECM (PCM) decreases the amount of fuel injection, which causes oxygen concentration in the exhaust gas to increase and electromotive force of the oxygen sensor to decrease. Then a lean signal is sent to ECM (PCM).
3. As ECM (PCM) increases the amount of fuel injection according to the lean signal, oxygen concentration in the exhaust gas decreases and the situation is back to above 1).
4. ECM (PCM) detects O2 concentration in the exhaust gas converted by TWC from HO2S-2 and compensates the fuel injection volume as in 1) - 3) above.
Above described process 1) through 3) does not take place under following conditions.
- When engine coolant temp. is low
- At fuel cut
- At high engine load
Also, what described in 4) does not take place under following conditions. Process 1) through 3) not taking place
- HO2S-1 is deactivated or faulty
- HO2S-2 is deactivated or faulty
- HO2S-1 heater faulty
- HO2S-2 heater faulty
- At idle speed