Table of contents: General information ↓ Preliminary checks ↓
Please also refer to Section Troubleshooting and the following Sections.
The ignition system and the fuel system are interconnected components of the engine management system. Therefore, some components perform several functions related to the operation of different parts of the engine management system.
General information
The ignition system and the fuel system have a common diagnostic system designed to store fault codes and perform diagnostics. When a fault occurs, the control unit records a certain sequence of signals in memory (fault code), which can subsequently be considered a special device (refer to the Section for a description of the fuel system inspection procedure).
If there are malfunctions in the operation of the car engine, the cause can most likely be found out by examining the memory of the control unit. After reading the fault codes, it is possible to find out which unit is faulty and perform the appropriate tests (either the unit itself or its wiring).
Visual inspection of the wiring and connectors is not enough - be sure to read the information stored in the control unit's memory.
Preliminary checks
If the malfunction occurs shortly after servicing a component, first carefully inspect the component and its surroundings. The cause may be a poorly installed component or a poorly connected connector.
If you are trying to diagnose a specific engine problem, such as a loss of power, in addition to the steps below, measure the cylinder compression. Make sure the fuel filter and air cleaner have been changed at the recommended intervals.
Please note that after reading the fault codes, they must be deleted from the control unit memory using the same diagnostic scanner, and then the fault must be eliminated.
Open the hood and check that the battery terminals are securely connected and that there is no corrosion on them. If there is any corrosion or damage, replace or clean the wires. Similarly, check all grounding straps to make sure they are making good contact (the mating surfaces must be absolutely clean and free of any traces of corrosion) with a body or engine.
After this, carefully inspect all visible wiring laid inside the engine compartment. Make sure that all connections are secure. At this stage, you are interested in obviously damaged wires. They can be cut or chafed against sharp or moving engine components, such as suspension parts or a drive belt. A wire can break as a result of careless installation of a component. The wire can melt upon contact with the exhaust system. The most likely cause of damage to the wiring is improper routing of its bundles in the engine compartment after repair or maintenance of a component.
Wires may be damaged or shorted without damage to their insulation. In this case, inspection will not lead to anything. Such damage can occur after pulling the wires or improperly placing the wiring inside the engine compartment. If you think such damage is possible, check the wire using the sequence below.
A damaged wire can be repaired by soldering a piece of new wire into the break. Soldering is necessary to obtain a reliable contact. Insulation can be restored with a sufficient amount of electrical tape or heat shrink tubing. If the damage is significant and the damaged wire plays a significant role, the most reliable way out is (although quite expensive) the corresponding harness will be replaced with a new one.
After repairing the damaged wire, place it correctly in the engine compartment, away from rotating and hot parts. Do not forget to secure the wire in intermediate clamps (if any).
Make sure all accessible connectors are secure and clean. All fasteners must be installed. If you notice any signs of corrosion on the inner surface of the connector (white or green deposits, as well as traces of rust) or excessive contamination, remove it from the corresponding terminal and clean it thoroughly. You can use a special aerosol for this. If the connector is seriously damaged, it should be replaced. Keep in mind that in some cases you will have to replace the entire harness.
If you were able to completely remove traces of corrosion from the connector, fill it with preservative grease, then install it in place. You can find out the type of grease at the service station.
All models are equipped with a crankshaft position sensor (it is also used to determine the TDC of the first cylinder). Its working part may be contaminated with oil or dust, which can lead to malfunctions and, accordingly, misfires.
Carefully inspect all vacuum hoses and tubes located in the engine compartment. Make sure that the clamps are securely tightened and that there are no cracks, delaminations or signs of damage on the hoses themselves. Also make sure that no hoses are pinched or bent too much, i.e. do not let air through. Pay special attention to hoses located near sharp edges, as well as the ends of all hoses. All damaged hoses must be replaced.
Make sure there are no signs of damage or contamination on the crankcase ventilation hoses. Also make sure that they are not blocked from the inside. The number and location of the system hoses depends on the car model, but all models have a hose that connects the top of the engine to the air intake hose or intake manifold. The system hoses also connect the cylinder block (or oil filler neck) with an intake manifold. These hoses deliver oil vapors to the combustion chambers. If these hoses are dirty or blocked, the engine will run unstably (especially at idle).
Following from the fuel tank through the fuel filter to the fuel distribution line along the fuel lines, carefully inspect them. If signs of damage or kinks are found, replace the corresponding section. Pay special attention to the pipe connections. Cracks may appear on them, leading to fuel leaks.
Remove the air cleaner housing cover and inspect the element. It should be relatively clean and dry. A heavily soiled air cleaner will provide significant airflow resistance, resulting in a noticeable reduction in engine power. Replace the air cleaner if necessary.
Start the engine and let it idle.
Warning: When performing any work in the engine compartment with the engine running, use extreme caution. In addition to the high risk of burns from hot engine or exhaust components, you risk serious injury from rotating parts (for example, a radiator fan or a drive belt). Before starting work, first of all, take the measures and observe the safety precautions described at the beginning of each Chapter. Watch your hands, do not allow long hair or clothing to get into the engine compartment. Stay away from the exhaust system and other hot parts.
From the air intake to the air cleaner and then to the throttle body, check for leaks in the air supply hoses (including nearby vacuum hoses). They can be detected by a characteristic whistling sound. If there is no whistling sound, apply a small amount of soapy water to the suspect section of the hose. If the hose is damaged, 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 clamp securely or replace the damaged hose.
Check the entire exhaust system in a similar manner (from manifold to rear section). Make sure there are no gas leaks. To make the job easier, you can lift the car on a lift, place it on a ramp or over a pit. To perform the simplest check, plug the exhaust outlet and listen to the system. If you hear a characteristic whistle, there is a leak. If a leak is detected, tighten the appropriate clamp, bolts or nuts, replace the gasket or burnt section.
Further testing involves moving each connector one by one on the corresponding terminal with the engine running. An unreliable contact will be determined by a change in the nature of the engine's operation. Restore the reliability of the contact by replacing or cleaning the corresponding connector. Keep in mind that in some cases, entire harnesses will have to be replaced.
If, as a result of preliminary checks, you have not found the cause of unstable engine operation, the car should be taken to a service station for a more thorough diagnosis using special equipment.
(The original article is available on the online resource: «AUDIMANUAL»)