COMPUTER SYSTEMS IN INJECTION
The most common components that make electronic injection controllers exchange trends and basic tests to identify faults in the subsystems that compose it.
This note aims to give a practical overview of the basic components of the drivers that drive the fuel-air ratio engines usually called internal combustion calculator, computer or ECM (Engine Control Module). There is a fundamental difference between the concept of computer and controller is as follows:
The computer reads and performs operations related to computer data, for example the CD reading - ROM, and screen display. The controller reads and performs operations related to industrial processes, as an example measure the temperature sensor and drives the injector.
The first drivers were only shot timers (Peugeot 505 SRI) analog (voltmeter needle) in which there is no intelligence available, with the advance of digital electronics (digital voltmeter) displayed the true controllers (Peugeot 405 SRI) able to self-diagnose and resolve emergency situations. The problems were resolved over time were:
• analog conversion (sensors), digital (microcontroller).
• stable voltage sensors (internal source).
• Suppression of background noise and battery.
• Devices for high power actuators
• Devices for high voltage actuators.
• Diagnosis by Scanner and self diagnosis.
• Self of the individual components. We have two drivers
different injection to extract them common components and analyze where we can check and verify the issues that determine the malfunction of this component. First electronics always verify the feeding problems which developed this topic by checking the components that make the controller receives the 13.6 V battery.
Magneti Marelli In the controller we have a 1000 uF capacitor and a varistor 25v X (a device that varies its resistance as a function of the applied voltage for voltages greater than 25V is a short circuit), while the driver EEC - IV is a surge protector and a capacitor of 3.3 uF 63V X outstanding characteristic of the suppressor is a device Semiconductor quick reaction to the surge voltage exceeding 25V induction caused by voltage from the alternator or the ignition circuit also provides protection against reverse polarity.
often have often seen this surge in short because he reversed the polarity of the battery which provides protection to the rest of the controller to replace it is difficult because the market is not available, is replaced by a 1N5400 diode (3A and 50V). In the case of varistor no problem as this commercially available, in this case if it does reverse polarity destroys the input capacitor and no protection.
Another important circuit is the input from sensors that are characterized by RC type circuit or a peak suppression at each entrance.
appear in those cases where RC circuit (temperature sensors) may appear as a resistance characteristic failure cut or cold welding (contact failure), the solution is generally difficult to handle because the components of the type SMD (Surface Mount Devices ) are placed on both sides of the PCB, but with patience can be detected in the auto sensor which does not react and thus know which pin of the circuit response and verify the input circuit, ie if the resistance is the appropriate value may be replaced by resistors metal film of equal value without problems.
For failures caused by the capacitor solutions are few circuital level because we can only check that has been shorted (the type of polycarbonate capacitors is hardly short this failure characteristic of mica-type capacitors silver )
Another circuit of interest is the 5V power supply in the photo No.: 1 it is clear that the 5-pin integrated circuit. This circuit has very special characteristics because it only feeds the temperature sensors, absolute pressure sensor, also etc.Sino microcontroller and logic circuits control. The source generally has five pins as It turns off if an excess of power to provide protection to the system, a general reset when there is contact from the ignition key.
One peculiarity is that they are low voltage regulators between the inlet (13.6 V) and output (5V), which allows it to work under very aggressive entry (7V) to provide 5V to the entire system without inconvenientes.Estos circuits are available in the electronic marketplace and are easily replaceable. It is here
clarification when you work on these drivers all checks can be made with tops discovered but it is recommended that one is connected to a mass of security so there is no possibility of electricity static (remember that can generate voltage differences close to 2500V).
also recommend the use of ceramic art welders because the insulation resistance is greater than 30 Mohms, and thus ensure not induce stresses in the components to be replaced, a further clarification: NEVER REPLACE A COMPONENT WITH THE DRIVER FIRED.
Another component often seen in the drivers are integrated circuits that drive the stepper motors or valves ISC
The key feature of these circuits is that they are able to control themselves, this means that if problems of excess power to excite motor, the circuit is shut down to avoid being destroyed, to detect this fault is to replace the motor windings resistance equivalent (for the motor Marelli value is 52 Ohms, but there is no market, use resistance of 47 Ohms 2W in their place, and observe the oscilloscope signals (quadrature signals obtained with reverse polarity).
A useful tip never try to test the system idle without putting in place a resistance because circuits generally are called "open collector (open collector), in a nutshell not work without closing the charging circuit.
Finally appear injection and ignition circuits where we find the output transistors as shown in the following photos for driver Marelli and EEC - IV.
The characteristics of these are totally different and can not be replaced each other, because while the injection transistor is of NPN type isolation is 120V and 8A of output current of the NPN transistor is switched on but insulation 450V and 16A load current.
If they can be replaced by transistors which are in the market. To test I recommend to use the driver on the circuit in operation since the tester in the diode position is not always their fault.
The checkpoint is at the base of Tr. and is characterized as follows:
a) In general have three terminals.
b) One end is ground Through resistance.
c) The other side is the base, 1V square wave amplitude.
d) The middle terminal is the collector and goes to the load circuit (nozzle).
The current trend is to replace Tr. by intelligent devices so as to reduce the size of the output circuit, these new devices are used in centralized systems door and have a great advantage if the load conditions (whether injectors, engine coils, ignition coils) in terms of current, temperature, voltage and power do not exceed the values \u200b\u200bdefined by the manufacturer, and instead of destroying what they do is block saving the semiconductor output. Before the end
article I provide a case that happened to me on the controller Magneti Marelli, the fault that is stopping the vehicle presented at random.
I could see the car when they left was because of lack of power, the first thing I did was replace Tr, then to check the old man did not find anything wrong, so that leaves open the driver and found the base of Tr. when it was installed in the car there I realized that at the time that I went up to the base pulse arrives, driver final conclusion impossible to repair.
In short, all serve to discriminate which is the device to fail and to determine the maximum certainty that is what is broken.
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