Attention! When working on the fuel system, you must first remove the pressure in the system.
Relieve pressure in the fuel system
1. Remove ground wire from battery.
2. Slowly loosen the union nut in the fuel line to relieve pressure in the fuel system.
3. An alternative method of relieving pressure in the fuel system is to remove either the fuel pump fuse or the fuel pump relay and run the engine at idle to a stop. After completing work on the fuel system, install the previously removed fuse or relay.
Examination
1. Check that the wires are connected securely and that there is no corrosion.
2. Check the condition of the air filter and spark plugs.
3. Check the compression pressure in the engine cylinders.
4. Check ignition timing setting.
Adjustment
Bosch L3.1 and MP3 systems. 1
Before adjusting, set the idle speed and fulfill the following conditions:
- the ignition system must be in good condition and properly adjusted;
- the air filter must be clean;
- the initial throttle positions are correctly adjusted;
- the throttle switch is correctly adjusted;
- the engine should be warm, the cooling fan should turn on and off once.
1. Adjust the idle speed with the throttle screw. Turning the screw clockwise decreases the idle speed, counterclockwise increases the speed.
2. Install the exhaust gas analyzer on the vehicle in accordance with the manufacturer's instructions.
3. Adjust the composition of the fuel mixture (SO), by turning the air flow meter screw. To access the screw, you must first remove the cap from it.
4. Adjust idle speed.
Bosch ML4.1 system
The idle speed is not adjustable. It is controlled by the idle speed control valve.
1. Install the exhaust gas analyzer on the vehicle in accordance with the manufacturer's instructions.
2. Adjust the composition of the fuel mixture (SO), by turning the air flow meter screw. To access the screw, you must first remove the cap from it. Turning the screw clockwise increases the CO content, while turning it counterclockwise decreases it.
Bosch LU2-Jetronic system
Idle speed adjustment screw (LU2-Jetronic system)
2 - idle speed adjustment screw
The idle speed is adjusted as described for the Bosch L3.1 system (see above).
The composition of the fuel mixture is automatically adjusted by the device according to the signals from the oxygen sensor.
Bosch Motronic M1.3 system
Idle speed is adjustable only on engines with 8 valves; on engines with 16 valves, the idle speed is controlled by the ECU.
1. Adjust the idle speed with the throttle screw. Turning the screw clockwise decreases the idle speed, counterclockwise increases the speed.
2. Install the exhaust gas analyzer on the vehicle in accordance with the manufacturer's instructions.
3. Adjust the composition of the fuel mixture (SO), by turning the air flow meter screw. To access the screw, you must first remove the cap from it.
Systems MM8P, Sagem-Lucas 4GJ, Bosch Motronic 5.1, Bosch Motronic 3.2
The systems are not regulated. If the idle speed or the composition of the mixture is not correct, then the control unit is damaged.