Pic. 2.363. Scheme of switching on the operation of the nozzles
General information
Multiport fuel injection system (MFI) consists of sensors that evaluate the condition of the engine, an electronic engine control unit (RSM), which, in turn, controls the entire system based on the information received from sensors and actuators, which are triggered by commands from the PCM. The PCM controls the fuel supply to the engine cylinders, the air flow at all engine idle speeds and the ignition timing. Moreover, the PCM has several self-diagnostic modes that make troubleshooting easier when they occur.
Fuel management
The injector control pulse width and ignition timing are selected to provide the optimum air-fuel ratio under constantly changing engine operating conditions. The intake port of each cylinder has one injector. Fuel is supplied by the fuel pump under pressure to the fuel manifold. To maintain the required pressure in the system, a pressure regulator is provided. Fuel under pressure is supplied to the injectors. Such a fuel supply system is called distributed. Typically, fuel is injected by the injector once every two revolutions of the crankshaft. The electronic engine control unit enriches the composition of the mixture during operation «no feedback» when the engine is cold or under heavy load. If the engine is warm or running at normal load, PCM, when the mode is turned on «feedback» through an oxygen sensor with a heater, creates a stoichiometric composition of the mixture, which ensures the best engine performance in terms of «purity» exhaust gases using a three-way catalytic converter.
Engine idle control
Idle speed is maintained at an optimal level by controlling the amount of air passing through the bypass duct in accordance with changes in idle conditions and engine load. PCM controls the servo (stepper motor) idle speed controller (ISC), maintaining the idle speed at a predetermined level determined by the temperature of the coolant in the engine and the load from the air conditioner. Moreover, when the air conditioner is off and during idle operation, the stepper motor of the regulator adjusts the flow area of the bypass channel in such a way as to exclude fluctuations in the idle speed of the engine during an accidental change in load.
Ignition timing control
Pic. 2.364. Injector opening signal duration diagram
The power transistor of the ignition system, installed in the primary circuit of the system, turns on and off to change the current in the primary circuit of the ignition coil. This provides control of the change in the ignition timing and maintains its optimal value when changing the engine operating mode. The ignition timing varies by PCM depending on the engine speed, filling the cylinders with air, coolant temperature and atmospheric pressure (barometric) pressure.
Fuel pump control
Turning on the fuel pump relay so as to supply current to the pump when the engine is cranked by the starter and during normal operation.
Control of the electromagnetic clutch for turning on the air conditioning compressor
Turning on and off the electromagnetic clutch of the air conditioning compressor.
Fan relay controls
The speed of the cooling system fan and the air conditioning condenser fan change according to changes in coolant temperature and vehicle speed.
Diagnostic Mode
If a malfunction occurs in any sensor or actuator associated with the toxicity reduction system, the engine malfunction indicator lamp lights up («CHECK ENGINE»), which informs the driver of a malfunction.
If a malfunction occurs in any sensor or actuator, a diagnostic code corresponding to this malfunction appears.
RAM data («RAM») an electronic engine control unit, from sensors and actuators, can be read by a diagnostic tool. Finally, actuators can be actuated and tested independently of the system itself.
Instructions for checking blown fuses
Remove the fuse and measure the resistance between the loaded side of the fuse and «weight». Set the switches of all circuits that connect to this fuse to the position «included». If the resistance is close to 0 ohms, then there is a short circuit between these switches and the load. If this resistance is different from 0 ohms, it means that there is no short circuit in the circuit at the moment, but the momentary shorting of the circuit causes the fuse to blow.
The main causes of a short circuit are as follows:
- destruction of the wiring on the car body;
- damage to the insulation of the wiring due to wear or heat;
- water intrusion into a connector or circuit;
- human factor (erroneous circuit connection).
Checking the system of distributed fuel injection
If the components (sensors, engine control unit, injectors, etc.) multiport fuel injection systems (MFI) are faulty, the result will be a cut in fuel supply or a failure in accurate fuel supply under various engine operating conditions. The following situations may occur:
- the engine does not start or starts with difficulty;
- unstable engine idling;
- poor engine control.
When these symptoms appear, you must first diagnose the car.
Diagnostic operations on the car
DTC storage: After the PCM detects a malfunction for the first time, a diagnostic code is stored and the malfunction is re-detected when the engine is restarted. (The malfunction is determined during the driving cycle of the car). However, for the case of the fuel system (rich/lean mixture, misfiring), the DTC will only appear the first time the problem is determined.
Clearing Diagnostic Trouble Codes: After the DTC is stored, and if the PCM does not detect the same problem again within the next 40 driving cycles, the DTC will be cleared from the PCM's memory. However, for the case of the fuel system (rich/lean mixture, misfiring), the diagnostic code is cleared when the following two conditions are met:
- When driving conditions (engine speed, coolant temperature, etc.) are identical to those in which this fault was first detected.
- When the PCM does not detect this fault again within the next 80 driving cycles.
Note. «driving cycle» called the state of the engine in which it passes the mode of operation «with feedback».
Engine Malfunction Indicator Lamp (MIL)
Pic. 2.365. Malfunction indicator lamp
When the check engine light comes on (MIL), this means there is a problem with the vehicle.
However, if no repair action is taken, the MIL will automatically turn off after 3 consecutive driving cycles.
After the ignition is turned on, the MIL comes on and stays on for about 5 seconds to indicate that the lamp is good.
Turning on the MIL may indicate the presence of malfunctions in the following elements:
- catalytic converter;
- fuel system;
- air flow sensor (MAF);
- intake manifold air temperature sensor (IAT);
- coolant temperature sensor (ECT);
- throttle position sensor (TPS);
- front oxygen sensor;
- rear oxygen sensor heater;
- rear oxygen sensor;
- front oxygen sensor heater;
- nozzles;
- misfiring;
- crankshaft position sensor (TFR);
- camshaft position sensor (SMR);
- fuel vapor recovery system;
- vehicle speed sensor (VSS);
- idle speed controller (ISC);
- electronic engine control unit (RSM);
- absolute sensor (barometric) intake manifold pressure (MAP) (except vehicles with 2.7L V6 engine);
- sensor-switch of the fully closed throttle valve;
- exhaust gas recirculation system (except vehicles with 2.7L V6 engine).
Verification
Turn on the ignition (ignition key position «ON») and check that the check engine light comes on for about 5 seconds and then turns off.
If the test lamp does not light, then check the wiring for an open, the fuse and the lamp itself for burnout.
Self-diagnosis
ECM monitors input/output signals (some permanently, others only under certain conditions). In the event that the electronic engine control unit has detected a malfunction (permanent or temporary disruption of the system), then it will write the corresponding fault code into memory and send a signal to the standard diagnostic connector. Diagnostic results (fault codes) can be read with an engine fault indicator light or a HI-SCAN tester (Pro). Fault codes will be stored in the memory of the electronic engine control unit only when there is battery power. Fault codes can be erased either by disconnecting the battery terminal or engine control unit connector, or using the HI-SCAN tester (Pro).
Verification procedure (self-diagnosis)
Note. If the battery is low, the diagnostic codes cannot be read. Monitor battery health (board voltage), recharge the battery before testing.
Note. DTCs are cleared when the battery or PCM connector is disconnected. Do not disconnect the battery until all trouble codes have been read and analyzed.
Test Method (when using diagnostic tool type GST)
Pic. 2.366. Diagnostic connector pins
Switch off the ignition.
Connect the scan tool to the data link connector (diagnostic connector).
Turn on the ignition.
Using a scan tool, read the trouble codes.
Carry out the necessary repairs in accordance with the recommendations of the diagnostic card.
Erase diagnostic codes.
Disconnect the diagnostic tool.