K-Jetronic: Troubleshooting Symptoms

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K-Jetronic: Troubleshooting Symptoms

K-Jetronic is a mechanical system:  the fuel is continuously metered in proportion to the quantity of air drawn in by the engine.  The K-Jetronic system was installed as Original Equipment in series production vehicles in the years 1973 through 1995.  Since then, the K-Jetronic system has been only of significance for repairs and maintenance.

Symptoms:

Engine does not start/starts hard when cold

Engine does not start/starts hard when warm

Irregular idle during warm-up

Irregular idle with warm engine

Engine will not accelerate, backfires

Engine backfires under load

Poor Performance

Engine runs on

Fuel consumption too high

Driving performance unsatisfactory

CO concentration at idle too high

CO concentration at idle too low

Idle speed cannot be adjusted (too high)

Engine starts but immediately dies

 

Symptom: Engine does not start/starts hard when cold

Cause
 Remedy
Sensor plate and/or plunger not moving freely Check for free movement
Auxiliary air valve does not open Check valve for correct function
Electric fuel pump not operating Check pump fuse, pump relay and pump
Cold start system defective Check cold start system
Therm-time switch defective Test thermo-time switch
"Cold" control pressure outside tolerance Test pressure
Injector leaking, opening pressure low Check injectors on tester
Injected fuel quantities unequal Check for equal fuel quantities
Basic idle setting incorrect Check and adjust CO level

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Symptom:  Engine does not start/starts hard when warm

Cause
 Remedy
 
Leaks in air intake system (false air) Check air system for leaks
Sensor plate and/or plunger not moving freely Check for free movement
Air flow sensor plate stop incorrectly set Check and reset
Electric fuel pump not operating Check pump fuse, pump relay and pump
"Warm" control pressure too high Test pressure
Fuel system leakage Inspect fuel system for leaks
Injector leaking, opening pressure low Check injectors on tester
Injected fuel quantities unequal Check for equal fuel quantities
Basic idle setting incorrect Check and adjust CO level

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Symptom:  Irregular idle during warm-up

Cause
 Remedy
Leaks in air intake system (false air) Check air system for leaks
Auxiliary air valve does not open Check valve for correct function
Cold start valve leaking Check cold start valve
"Cold" control pressure outside tolerance Test pressure
Injector leaking, opening pressure low Check injectors on tester
Injected fuel quantities unequal Check for equal fuel quantities
Basic idle setting incorrect Check and adjust CO level
Lambda control system not functioning correctly Check Lambda control system

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Symptom:  Irregular idle with warm engine

Cause Remedy
Leaks in air intake system (false air) Check air system for leaks
Sensor plate and/or plunger not moving freely Check for free movement
Cold start valve leaking Check cold start valve
"Warm" control pressure too high Test pressure
"Warm" control pressure too low Test pressure
Injector leaking, opening pressure low Check injectors on tester
Injected fuel quantities unequal Check for equal fuel quantities
Basic idle setting incorrect Check and adjust CO level
Lambda control system not functioning correctly Check Lambda control system

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Symptom:  Engine will not accelerate, backfires

Cause Remedy

Leaks in air intake system (false air) Check air system for leaks
Sensor plate and/or plunger not moving freely Check for free movement
"Warm" control pressure too high Test pressure
"Warm" control pressure too low Test pressure
Basic idle setting incorrect Check and adjust CO level
Lambda control system not functioning correctly Check Lambda control system

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Symptom:  Engine backfires under load

Cause Remedy

Sensor plate and/or plunger not moving freely Check for free movement
Electric fuel pump not operating Check pump fuse, pump relay and pump
"Warm" control pressure too high Test pressure
Primary system pressure out of tolerance Test pressure and adjust with shim
Injector leaking, opening pressure low Check injectors on tester

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Symptom:  Poor Performance

Cause Remedy

Leaks in air intake system (false air) Check air system for leaks
Sensor plate and/or plunger not moving freely Check for free movement
"Warm" control pressure too high Test pressure
"Warm" control pressure too low Test pressure
Primary system pressure out of tolerance Test pressure and adjust with shim
Injected fuel quantities unequal Check for equal fuel quantities
Throttle butterfly does not open completely Check butterfly and stops in throttle venturi
Lambda control system not functioning correctly Check Lambda control system

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Symptom:  Engine runs on

Cause Remedy

Sensor plate and/or plunger not moving freely Check for free movement
Air flow sensor plate stop incorrectly set Check and reset
Cold start valve leaking Check cold start valve
Injector leaking, opening pressure low Check injectors on tester
Basic idle setting incorrect Check and adjust CO level

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Symptom:  Fuel consumption too high

Cause Remedy

Cold start valve leaking Check cold start valve
"Warm" control pressure too low Test pressure
Basic idle setting incorrect Check and adjust CO level
Lambda control system not functioning correctly Check Lambda control system

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Symptom:  Driving performance unsatisfactory

Cause Remedy

Leaks in air intake system (false air) Check air system for leaks
Sensor plate and/or plunger not moving freely Check for free movement
Excessive fuel delivery to control circuit Check fuel delivery
"Warm" control pressure too high Test pressure
"Warm" control pressure too low Test pressure
Primary system pressure out of tolerance Test pressure and adjust with shim
Basic idle setting incorrect Check and adjust CO level
Lambda control system not functioning correctly Check Lambda control system

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Symptom:  CO concentration at idle too high

Cause Remedy

 Sensor plate and/or plunger not moving freely Check for free movement
Cold start valve leaking Check cold start valve
"Warm" control pressure too high Test pressure
Basic idle setting incorrect Check and adjust CO level
Lambda control system not functioning correctly Check Lambda control system

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Symptom:  CO concentration at idle too low

Cause Remedy
Leaks in air intake system (false air) Check air system for leaks
Sensor plate and/or plunger not moving freely Check for free movement
Basic idle setting incorrect Check and adjust CO level
Lambda control system not functioning correctly Check Lambda control system

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Symptom:  Idle speed cannot be adjusted (too high)

Cause Remedy
Auxiliary air valve does not close Check valve for correction function

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Symptom:  Engine starts but immediately dies

Cause Remedy
Electric fuel pump not operating Check pump fuse, pump relay and pump
Excessive fuel delivery to control circuit Check fuel delivery
"Warm" control pressure too high Test pressure
"Warm" control pressure too low Test pressure
Primary system pressure out of tolerance Test pressure and adjust with shim

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