Attention. Since the VAZ-2108 car uses a high-energy ignition system, it is not allowed to disconnect high-voltage wires and check the ignition circuits for a spark while the engine is running, as this can lead to injury, as well as burnout of high-voltage insulation and failure of the ignition system.
For the same reason, it is not allowed to start the engine using a spark gap between the high voltage wire and the central terminal of the ignition distributor.
When servicing the car, check the reliability of the connections of the high voltage wires with the ignition distributor sensor, coil and spark plugs.
It is not allowed to disconnect the wires from the battery terminals while the engine is running, as this may damage the switch.
Proximity sensor
The performance of the non-contact sensor located in the ignition distribution sensor can be checked with an indicator assembled according to the diagram shown in fig. 138. The indicator uses resistors of the MLT type, 1 W; capacitors C1 type KLS1 and C2 type K.53-14. As an indicator lamp HL1, a car lamp A12, 3 W was taken. Instead of a KT816B transistor, you can use a KT814B type transistor. The indicator wires are soldered to a three-terminal block Ш1 of the same type that is connected to the ignition distribution sensor on the car.
Pic. 138. Indicator circuit for checking the operability of a proximity sensor in the ignition distributor sensor
To check the proximity sensor, connect the indicator to the ignition distribution sensor instead of the ignition system wiring harness and turn the engine with a starter or a special key for the bolt on the crankshaft. If the HL1 lamp flashes during rotation of the crankshaft, then the proximity sensor is working.
The serviceability of the proximity sensor can also be checked using a voltmeter according to the diagram shown on rice. 140.6. The verification procedure is described in the next chapter. This method is more accurate, as it allows you to check the magnitude of the voltage pulses generated by the sensor using a voltmeter.
Switch
The functionality of the switch can also be checked with a 3W A12 lamp. To check, it is necessary to disconnect the brown wire with red stripes from the ignition coil coming from the terminal «1» switch, and connect the tip of the wire to the test lamp. The other end of the lamp is connected to the terminal «DB» ignition coils and crank the engine with a starter. If the lamp flashes during rotation of the engine crankshaft, then the switch outputs current pulses to the ignition coil.
The described method allows only a rough estimate of the operability of the switch - whether it produces current pulses or not. Pulse parameters (size and duration, shape) cannot be verified by this method. And they can seriously affect the operation of the engine, especially at high engine speeds. Therefore, the following test of the switch on the bench using an oscilloscope and a rectangular pulse generator is more accurate.
Ignition coil and high voltage wires
The performance of these elements can be checked using a high-voltage arrester. The simplest spark gap consists of two pointed metal rods, the gap between which can be adjusted. The rods are fixed on a plate of insulating material (plastic or ceramic).
To check the ignition coil, the central high voltage wire is disconnected from the ignition distribution sensor and connected to the spark gap electrode. The second output of the arrester is connected to the car body and the air gap between the electrodes of the arrester is set to 7-10 mm. If, when the engine is rotated by the starter, uninterrupted sparking is observed between the electrodes of the arrester, then the ignition coil and the central high voltage wire are in good order.
By connecting the central wire to the ignition distribution sensor and connecting the wires leading to the spark plugs to the spark plug in turn, they similarly check the performance of these wires. In this case, there may be a violation of sparking when connecting all the wires, while when connecting the central wire to the arrester, sparking was normal. The cause of this phenomenon may be internal discharges in the ignition distributor sensor. It is possible that there are cracks or burnouts in the cover or rotor of the ignition distributor or their surfaces are dirty. You can verify the presence of this defect by replacing the ignition distribution sensor with a known good one.
Attention. It is strictly forbidden to carry out preventive work with the distribution sensor with the ignition on, since on a VAZ-2108 car the ignition system is a source of particularly high voltage.