Possible malfunctions of the L-Jetronic system, their causes and methods of elimination (Mercedes-Benz E-Class W123)

Contents: Faults 1-8 ↡ Malfunctions 9-17 ↡

Faults 1-8

1. The engine does not start (oil temperature is less than or equal to 20°C).

2. The engine does not start (oil temperature is greater than or equal to 60°C).

3. Difficulty starting the engine (oil temperature is less than or equal to 20°C).

4. Difficult starting (oil temperature is greater than or equal to 60°C).

5. The engine starts and stalls.

6. The engine runs unsteadily at idle when warming up.

7. The engine idle speed does not correspond to the nominal value.

8. The engine runs rough at idle.

Malfunction No								Check
1	2	3	4	5	6	7	8	Check
X	X	X		X				Fuel pump
X	X	X	X					Fine fuel filter
X	X	X	X	X	X			Injector injection pressures
X	X	X	X	X	X			Fuel pump discharge pressure
		X		X			X	Fuel pump performance
		X					X	Fuel quality
		X		X	X	X		Additional fuel supply valve
X		X			X	X		Thermal time relay
		X	X		X	X		Starting nozzle
X	X	X	X	X	X	X	X	Injection nozzles
		X	X		X	X	X	Coolant temperature sensor
						X		Throttle switch
		X		X	X	X		Throttle body
		X	X		X	X		Pneumatic throttle actuator
X	X	X	X	X	X	X	X	Air flow meter
X	X	X	X	X	X	X	X	Electronic control unit
X	X	X	X	X	X	X	X	Electrical wires and their connections
X	X	X	X	X				Fuel pump relay
		X	X		X	X	X	Air filter
			X			X		Engine cooling system
						X	X	Tightness of connections in the engine intake tract
		X	X	X		X		No extraneous air flow into the engine
X	X	X	X	X	X	X		Engine intake tract
								Lack of combustible mixture at partial engine load

Malfunctions 9-17

9. The engine "shakes" when accelerating.

10. The engine "shakes" when moving at a constant speed.

11. The engine "shakes" at forced idle.

12. Knocking in the engine when increasing the crankshaft speed.

13. The engine does not have sufficient responsiveness.

14. Increased fuel consumption.

15. Increased content of carbon monoxide and hydrocarbons in exhaust gases at idle.

16. Reduced content of carbon monoxide and hydrocarbons in exhaust gases at idle.

17. The engine does not develop full power.

Malfunction No									Check
9	10	11	12	13	14	15	16	17	Check
				X				X	Fuel pump
X	X			X			X		Fine fuel filter
X	X			X			X	X	Injector injection pressures
X	X			X			X		Fuel pump discharge pressure
X	X			X					Fuel pump performance
X	X		X	X	X			X	Fuel quality
					X				Additional fuel supply valve
				X	X	X			Thermal time relay
	X			X	X	X		X	Starting nozzle
X	X	X		X	X	X	X	X	Injection nozzles
X	X	X		X	X	X	X	X	Coolant temperature sensor
				X	X	X		X	Throttle switch
						X	X	X	Throttle body
						X			Pneumatic throttle actuator
X	X	X	X	X	X	X	X	X	Air flow meter
X	X	X	X	X	X	X	X	X	Electronic control unit
X	X	X	X	X	X	X	X	X	Electrical wires and their connections
		X							Fuel pump relay
X	X			X	X	X	X	X	Air filter
X	X	X		X	X	X		X	Engine cooling system
X	X			X					Tightness of connections in the engine intake tract
	X			X			X	X	No extraneous air flow into the engine
X	X			X			X	X	Engine intake tract
X				X	X	X		X	Lack of combustible mixture at partial engine load