K Jetronic Troubleshooting

[nutz4benz]

Troubleshooting

Engine turns but won't start

1) No fuel pressure;
Test the fuel pump and pre-pump and do a fuel pressure test and volume test.

2) Jammed or sticking airflow sensor;
Remove the hose that goes to the intake and loosen the center line on the fuel distributor.This will relieve the control pressure.Press down on the center bolt of the plate and you should feel no resistance or binding.Also check for the correct centering and rest height.

3) Auxillary valve is sticking.

4) Defective cold start injector;
If the injector does not function,the air-fuel ratio will be lean.

5) Shorted or defective thermo-time switch;
The cold start injector will not work if the thermo time switch is defective.Check this in the event that your cold start injector failed the test before replacing in vain.

6) Control plunger sticking;
Remove the fuel distributor from the airflow sensor and check to see if it sticks are has severe tarnishing. (Note...Do not use a control plunger from another airflow sensor because these are machined to each airflow sensor they are originally installed in)

7) Restricted Injectors;
For this to be the cause,they would have to be severly restricted.

[nutz4benz]

Troubleshooting

Hot Starting Difficulty

1) Loss of rest pressure;
Perform a pressure test and focus on the rest pressure.If it does not pass,check for a defective fuel pump check valve,defective fuel distributor,faulty system pressure regulator and leaking cold start injector.

2) Airflow sensor improperly adjusted;
Check height,centering and for binding. Loosen the center line on the fuel distributor to relieve control pressure.

3) Sticking or binding control plunger;
Remove the fuel distributor and ensure that the control plunger moves freely.

4) Injectors leaking;
Remove the injectors from the intake manifold and with the ignition key on and engine NOT running,press on the center plate to pressurize the system.Inspect and replace any injectors that are leaking.

5) Cold start injector leaking;
Same test as above.

6) Shorted thermo-time switch;
Cold start injector is dependant on this component functioning.

7) Incorrect control pressure;
Perform a pressure test and verify that the warm control is within specs( specs posted at end of thread)

[nutz4benz]

Troubleshooting

Rough Idle ( Cold )

1) Cold control pressure incorrect;
The movement of the control plunger will be limited if the cold control pressure is high.This in turn will limit the amount of fuel able to be delivered through the injectors.The result will be an extremely lean air-fuel ratio.

2) Auxillary air valve defective;
If defective and not opening,idle cannot raise and results in a rough idle.

3) Airflow sensor adjusted improperly or is binding;
If the movement is not smooth,it will result in air-fuel ratio errors.

4) Leaking cold start injector;
If the cold start injector is leaking,the engine will be overfueled.

5) Injectors have an unequal flow or spray pattern;
Perform an injector flow test and replace any injectors that do not deliver the correct amount of fuel or have a poor spray pattern.

[nutz4benz]

Troubleshooting

Runs rough ( Warm )

1) Warm control pressure incorrect;
Incorrect warm control pressure that is too high or low will cause incorrect air-fuel ratio thus resulting in rough idle.

2) Airflow sensor adjusted improperly or is binding;
If the movement is not smooth,it will result in air-fuel ratio errors.Check and correct rest height and also centering of the plate.

3) Leaking cold start injector;
Again,this will result in overfueling the engine causing rough idle.

4) Injectors have an unequal flow or spray pattern;
Perform an injector flow test and replace any that do not deliver the correct amount of fuel or have a poor spray pattern.

[nutz4benz]

Troubleshooting

Stalls After Starting ( Warm )

1) Warm control pressure;
If the warm control pressure is too high or low,the air-fuel ratio will be lean.

2) System pressure incorrect;
If too high or low,the air-fuel ratio will be incorrect.

[nutz4benz]

Troubleshooting

Idle Speed High

1) Check auxillary air valve;
Ensure that it is closing.

2) Check for vacuum leaks;
Run a small unlit bottle of propane around throttle body and intake an if engine speed increases,you have located vacuum leak.

3) Check for minimum air.

[nutz4benz]

Troubleshooting

Backfire in Intake

1) Check that the CO adjustment is correct;
If incorrect,backfiring will result if started and under load.

2) Boot between airflow sensor and throttle body defective
This will result in a lean mixture due to secondary air.

3) Vacuum leaks.

[nutz4benz]

Troubleshooting

Misfiring

1) Ignition;
Inspect the cap,rotor,wires and plugs.

2) Fuel delivery inadequate;
Check for binding of the airflow sensor,control plunger, incorrect control or system pressure.

3) Injectors;
Unequal delivery or poor spray pattern.Perform a test and replace any that are defective

[nutz4benz]

Troubleshooting

Poor Power

1) Control pressure too high;
If the control pressure is too high,the control plungers travel will be limited resulting in a lean air-fuel ratio.

2) Check the ignition components;
Verify that the spark plugs,wires,cap and rotor are not worn.

3) Injectors restricted
Perform a test for delivery.If an injector is restricted,fuel delivery will be limited.

[nutz4benz]

Troubleshooting

Sag or Stumble When Accelerating

1) Airflow sensor plate binding or sticking;
If binding or sticking,fuel flow will be limited.

2) Control plunger binding or sticking;
If binding or sticking,fuel flow will be limited.

3) System pressure or warm control pressure incorrect;
If too high,the travel of the control plunger will be limited.

4) Injector flow unequal;
Perform an injector flow test and replace any injector that differs more than 10% than the others.