Mono-Jetronic, Mono-Motronic
If the engine does not start, you should always first check whether the valve injector is injecting fuel at all and whether there is an ignition spark.
The forced idle switch can only be checked with the engine running. The switch is designed to stop the fuel supply when the engine is running in forced idle mode (the car moves without touching the gas pedal), as soon as the crankshaft speed exceeds 1500 1/min.
Check fuse #18, replace if necessary.
By interrogating the memory device for fault codes, make sure that there is a speed signal from the Hall sensor to the control unit.
Check fuel pump performance, see below.
Injector check
Remove the intake air guide cover from the central injection system.
Ask an assistant to turn on the starter and at the same time check whether the valve injector is injecting fuel. The trace from the jet of fuel should be visible on the throttle valve.
If the injector does not inject fuel, check the resistance, the presence of supply voltage and the pre-resistance of the injector.
Press the locking metal clip and disconnect the plug -1- from the connector -2-.
Measure resistance of valve injector between middle pins of connector -2-. The prescribed value is 1.2-1.6 ohms. If the measured value does not match the prescribed value, replace the valve injector.
Attention: The prescribed value is indicated only for an ambient temperature in the range from +15°C to +30°C. If necessary, move the vehicle to a suitable location (garage) and wait for some time until the temperature of the valve injector reaches the specified value.
Check for supply voltage. To do this, connect a semiconductor diode lamp to both middle contacts of the plug -1- and turn on the starter. The LED should flash. If the LED does not flash, check the pre-resistance.
To do this, disconnect the plug of the pre-resistance circuit and check the resistance. The prescribed resistance value is 3-4 ohms. If necessary, replace the pre-resistor.
If no fault is found, perform an electrical check on the Mono-Jetronic system, see below.
Checking the forced idle switch
Warm up the engine to a coolant temperature of at least +60°C, then shut it off.
Remove the intake air guide cover.
Start the engine and let it idle. Make sure visually that there is a jet of fuel in the direction of the throttle valve.
Use the throttle lever to add gas and increase the engine speed to 3000 1 / min, and then quickly remove the gas and observe the fuel stream.
The fuel jet must be interrupted for a short time until the engine speed decreases again. This is a sign that the fuel switch is functioning.
Switch off the ignition and check the valve injector for leaks. Within a minute, no more than two drops of fuel should come out.
Screw in air guide cover.
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