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. Cold engine does not start.

2. A cold engine starts and stalls.

3. Hot engine does not start.

4. Difficulty starting a cold engine.

5. Difficulty starting a hot engine.

6. The engine runs unsteadily during warming up.

7. Violation of idle mode.

8. The engine starts and stalls.

Malfunction No								Cause of malfunction	Method of elimination
1	2	3	4	5	6	7	8	Cause of malfunction	Method of elimination
X		X						No fuel in the fuel tank	Fill the tank with fuel
X								The fuel pump is faulty	Check the operation of the pump, replace if necessary
X	X	X	X	X	X	X	X	The fuel filter is clogged	Wash the filter mesh or replace the filter
	X		X		X	X	X	The drain pipe is deformed or clogged	Straighten or blow out the fuel line
				X		X	X	Increased fuel pressure	Check the operation of the pressure regulator, replace if necessary
X	X		X		X	X	X	Low fuel pressure in the system	Check the operation of the pressure regulator, replace if necessary
X	X		X		X		X	Increased control pressure	Check the operation of the control pressure regulator, replace if necessary
	X	X		X	X	X	X	Reduced control pressure	Check the operation of the control pressure regulator, replace if necessary
X	X	X	X	X	X	X	X	Leaky injection nozzles	Replace injectors
							X	Injection nozzles are partially clogged	Replace injectors
X	X		X					The starting injector does not work	Check the starting injector, wires and their connections
X			X					Leaking starting nozzle	Replace the injector
							X	The thermal time relay is faulty	Replace the relay
			X					Coolant temperature sensor is faulty	Check the wires and their connections, replace the sensor if necessary
X	X		X		X		X	Throttle valve adjustment is out of adjustment	Adjust the initial position of the throttle valve
	X				X		X	The additional air supply valve does not close	Check the valve, replace if necessary
				X			X	Leakage in the air supply cap and/or air quantity meter	Check the intake system, replace if necessary
			X	X	X		X	Loosening of injection nozzles	Tighten the injectors
							X	Leakage in the exhaust system	Eliminate leaks in the system
							X	The spark plugs are faulty	Replace spark plugs
X		X	X	X	X		X	The ignition coil is faulty	Replace the ignition coil
X		X						The switch is faulty	Replace the switch
X		X						Break in ignition system wires	Replace damaged wires
								Incorrect ignition timing	Replace the switch
								Vacuum hoses are damaged	Replace damaged hoses
							X	The ignition timing regulator is faulty	Replace the ignition distributor sensor
X	X	X	X	X			X	Incorrect ignition timing	Adjust the ignition timing
X	X	X	X	X	X	X	X	The engine is subject to repair
X		X	X	X				Use of low octane gasoline	Use only fuel with the required octane rating
	X				X	X	X	Engine idle speed adjustment is out of adjustment	Adjust idle speed

Malfunctions 9-17

9. Backfires in the exhaust manifold.

10. The engine runs intermittently during acceleration.

11. The engine runs intermittently at forced idle.

12. Intermittent engine operation in all modes.

13. The engine does not develop full power.

14. Increased fuel consumption.

15. Violation of idle speed adjustment and CO content in exhaust gases.

16. Knocking of intake and exhaust valves during acceleration.

17. Increased content of hydrocarbons and nitrogen oxides in exhaust gases.

Malfunction No									Cause of malfunction	Method of elimination
9	10	11	12	13	14	15	16	17	Cause of malfunction	Method of elimination
									No fuel in the fuel tank	Fill the tank with fuel
									The fuel pump is faulty	Check the operation of the pump, replace if necessary
	X			X		X	X	X	The fuel filter is clogged	Wash the filter mesh or replace the filter
				X	X	X		X	The drain pipe is deformed or clogged	Straighten or blow out the fuel line
					X	X		X	Increased fuel pressure	Check the operation of the pressure regulator, replace if necessary
	X					X			Low fuel pressure in the system	Check the operation of the pressure regulator, replace if necessary
X	X			X		X	X	X	Increased control pressure	Check the operation of the control pressure regulator, replace if necessary
		X	X	X		X	X	X	Reduced control pressure	Check the operation of the control pressure regulator, replace if necessary
X	X	X	X	X		X	X	X	Leaky injection nozzles	Replace injectors
X			X		X	X	X	X	Injection nozzles are partially clogged	Replace injectors
	X		X	X		X	X	X	The starting injector does not work	Check the starting injector, wires and their connections
		X							Leaking starting nozzle	Replace the injector
X					X	X		X	The thermal time relay is faulty	Replace the relay
									Coolant temperature sensor is faulty	Check the wires and their connections, replace the sensor if necessary
X		X	X		X	X		X	Throttle valve adjustment is out of adjustment	Adjust the initial position of the throttle valve
	X								The additional air supply valve does not close	Check the valve, replace if necessary
X	X						X	X	Leakage in the air supply cap and/or air quantity meter	Check the intake system, replace if necessary
X	X			X		X	X	X	Loosening of injection nozzles	Tighten the injectors
					X	X	X	X	Leakage in the exhaust system	Eliminate leaks in the system
			X			X	X	X	The spark plugs are faulty	Replace spark plugs
	X		X	X		X		X	The ignition coil is faulty	Replace the ignition coil
	X		X	X				X	The switch is faulty	Replace the switch
	X		X	X				X	Break in ignition system wires	Replace damaged wires
	X		X	X		X		X	Incorrect ignition timing	Replace the switch
X	X		X	X					Vacuum hoses are damaged	Replace damaged hoses
X	X		X	X					The ignition timing regulator is faulty	Replace the ignition distributor sensor
X	X		X	X		X	X	X	Incorrect ignition timing	Adjust the ignition timing
X	X	X	X	X	X	X	X	X	The engine is subject to repair
	X		X	X			X		Use of low octane gasoline	Use only fuel with the required octane rating
					X	X	X	X	Engine idle speed adjustment is out of adjustment	Adjust idle speed