Contents: General information ⬇ Preliminary checks ⬇
See Section Diagnostics of malfunctions.
General information
The ignition system of the gasoline engine is integrated with the fuel injection system and is controlled by a single electronic control unit ECM (see Chapter Fuel, exhaust and emission control systems).
The ignition system and the fuel system have a common diagnostic system designed to detect violations, save fault codes and search for causes of failures. When a malfunction occurs, the control module writes it to the processor memory.
The cause of engine failures can most often be localized by reading the data stored in the memory of the ECM self-diagnostic unit. Once the failure is identified, you can proceed to check the condition and proper functioning of the relevant units and components. Remember that a visual check of the condition of the wiring and its connectors is not enough - be sure to read the information stored in the memory of the control module.
Preliminary checks
If the malfunction occurs shortly after servicing a component, first of all, carefully check the corresponding element. It is possible that the cause lies in carelessness in installing the component or connecting the electrical wiring connector to it.
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When investigating the cause of a drop in engine power, in addition to the checks listed below, also check the compression pressure in the cylinders (see Chapter Engines). It is possible that the reason for the decrease in the efficiency of the power unit is a careless attitude towards the implementation of such regular maintenance procedures of the car as replacing the fuel filter or the air cleaner filter element (see Chapters Vehicle settings and routine maintenance, Engines and Fuel, exhaust and emission control systems).
Remember that after reading the fault codes, the module memory must be cleared. Memory clearing is performed using the same device that is used when reading the codes (see section On-Board Diagnostic System OBD - General Information).
1. Open the hood and check the reliability of the fastening of the wire tips to the battery terminals. Make sure that there are no signs of oxidation of the terminals, if necessary, clean them (see Chapter Vehicle settings and routine maintenance). Check the reliability of the fixation of the terminal connections of the grounding buses and the quality of the electrical contact in them - the mating surfaces must be absolutely clean and free of oxidation products.
2. Carefully inspect all visible wiring laid inside the engine compartment, check the reliability of all electrical connections - pay attention to obvious signs of damage. In case of detection of cracks, cuts, abrasions of insulation, replace defective elements. Wire breakage can occur as a result of careless installation of any unit - the wire can melt upon contact with elements of the exhaust system. The most likely cause of wiring damage is incorrect wiring in the engine compartment after repair or maintenance procedures of any unit.
3. Wiring may be damaged or shorted even in the absence of obvious insulation damage, and external inspection will not yield results. This type of damage may occur after pulling out wires or improper placement of harnesses in the engine compartment.
4. Damaged wiring can be repaired by soldering a section of a new conductor into the gap - soldering is a necessary condition that guarantees reliable contact. Repair of damaged insulation is usually carried out using a sufficient amount of electrical tape or a section of heat shrink tubing. If the damage is significant, or the damaged wire plays a significant role, the most correct (although quite expensive) the solution would be to replace the corresponding harness.
5. After repairing the damaged electrical wiring, make sure it is laid correctly in the engine compartment - the harnesses should not touch the heated surfaces of the power unit. Do not forget to secure the wires in all the provided intermediate clamps.
6. Check the condition and reliability of fixation of all accessible contact connectors. All clamps must be installed. If oxidation products are detected on the inner surface of the connector, (white or green deposits, as well as traces of metal corrosion) or signs of excessive contamination, disconnect it from the corresponding terminal and clean it thoroughly, preferably using one of the special cleaning agents - ask in car accessory stores. Seriously damaged connectors are subject to replacement - sometimes together with the wiring harness connected to it.
7. After removing all traces of oxidation and dirt, fill the connector with preservative grease (consult a car service workshop) and install it in place, making sure that the connector is securely fixed.
8. All models are equipped with an inductive CKP sensor as standard, which provides the ECM with information about the engine speed and the TDC position of the piston of the first cylinder. Contamination of the sensing head of the sensor with oil or dust can cause misfires. For a description of the procedures for removing and installing the CKP sensor, see Chapter Fuel, exhaust and emission control systems.
9. Carefully examine the condition of all vacuum lines laid in the engine compartment. Check the reliability of tightening the fastening clamps, make sure there are no cracks, delamination or other damage to the hoses. Inspect the hoses for signs of obstruction (twisting, squeezing, bending, etc.). Pay special attention to hoses laid near sharp edges, as well as the condition of the sections pulled onto the fittings. Damaged hoses must be replaced.
10. Check the condition of the crankcase ventilation system (PCV) hoses. Make sure that there are no signs of patency problems. The number of hoses and where to install the system may vary depending on the vehicle model, but in any version of the model there is a hose connecting the upper part of the engine to the air intake sleeve or intake pipe. PCV hoses are usually connected to the intake pipe as well as the cylinder block (or oil filler neck) and serve to transport crankcase gases and oil vapors into the combustion chambers. Blocking the flow of these hoses usually leads to a disruption in the stability of the engine, especially at idle speed.
11. Moving along the fuel lines from the fuel tank to the fuel line, carefully examine the condition of the fuel system lines and their nipple connectors. If signs of damage or deformation are detected, replace the defective section. Particular attention should be paid to the condition of the line junctions, where cracks most often form, leading to the development of fuel leaks.
12. Check that the throttle cable is correctly routed and adjusted (see Chapter Fuel, exhaust and emission control systems). The cable should not bend too much. If you suspect that the cable assembly is not functioning properly, replace it.
13. Remove the air cleaner housing cover and check the condition of the filter element (see Chapter Vehicle settings and routine maintenance), if necessary, blow out or replace the dirty filter, since an increase in its resistance to flow can lead to a noticeable decrease in the power developed by the engine.
14. Start the engine and let it idle.
When performing any work in the engine compartment with the engine running, exercise extreme caution. Avoid touching hot surfaces of the power unit and moving components such as drive belts and the fan impeller. Always follow all necessary precautions and safety regulations.
15. Moving from the air intake to the air cleaner and further to the throttle body, check for signs of developing leaks in the intake air tract (including vacuum hoses). Leaks can be detected by a characteristic whistling sound - for greater reliability, wet the suspected area with a solution of soapy water. If the hose is damaged, the nature of the engine's operation will change, and bubbles will appear on the treated surface of the hose (or, depending on the pressure in the hose, water may begin to be sucked in). If a leak is detected, tighten the appropriate clamp or replace the damaged hose.
16. Drive the car onto the overpass/inspection pit (or jack it up and place it on supports) and carefully examine the condition of the exhaust system components from the exhaust manifold to the cut of the rear section. The sources of exhaust leaks are most easily identified by the appearance of a characteristic whistle when the exhaust port of the system is blocked - tighten the appropriate fasteners, or replace the burnt section.
17. Further testing involves moving each connector one by one on the corresponding terminal with the engine running. The unreliability of the electrical contact will be revealed by a change in the nature of the engine operation. Make the necessary corrections, replace the failed components - some connectors are replaced complete with the wiring harnesses connected to them.
18. If the cause of the malfunction cannot be identified during the above preliminary checks, the vehicle should be taken to a service station for a complete diagnosis of the control system using special equipment.
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