potentially useful k-jet info

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Nate
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potentially useful k-jet info

Postby Nate » Mon Jan 25, 2010 7:12 am

[mods, feel free to add this to the faq]
I have a 40 page pdf bosch kjet techical manual. if anyone wants a copy PM me your email address. don't post on this thread asking for it, as i'll probably not see it!!

i 'borrowed' this from another site. useful diagnostic info for the k-jet system, although the figures may not be correct as it is from a merc site - basically the same system though.


Troubleshooting K Jetronic


Engine turns but won't start

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

2)Jammed and/or sticking airflow sensor;
Remove the boot that goes to the intake and loosen the center line on 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 that the rest height and centering are correct.

3)Auxillary valve is sticking;

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

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 does not function before replacing.

6)Control plunger sticking;
Remove the fuel distributor from the airflow sensor and check to see if it moves freely.

7)Restricted injectors;
For this to be the cause,they would have to be severely restricted,which is why I listed it last.Do
an injector flow test and ensure that the delivery is
near equal.

Hot starting difficulty


1)Loss of rest pressure;
Do 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 adjusted incorrectly;
Check height,centering and for binding.Remove the boot and loosen the center line on fuel distributor to
relieve control pressure.

3)Sticking or binding of the 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/engine off,press on the center plate to pressurize the system.Inspect and replace any injector that is leaking.

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

6)Shorted thermo time switch;
Cold start injector is dependent of this component.

7)Incorrect control pressure;
Do a pressure test and verify that the warm control pressure is within spec.


Rough idle (cold)

1)Cold control pressure incorrect;
The movement of the control plunger will be limited if the cold control pressure is too high.This in turn will limit the amount of fuel able to be delivered through the injectors.The result will be a lean ratio and will cause rough idle.

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

3)Airflow sensor adjusted improperly or 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 even if cold.If the cold start injector is leaking,the idle will get worse as the engine temperature increases.

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


Runs rough (warm)

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

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

3)Leaking cold start valve;
Again,will result in overfueling the engine,resulting in a rough idle.

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


Stalls after starting (warm)

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

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


Idle speed high

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

2)Vacumm leaks;
Self explainatory.

3)Check the minimum air;
Self explainatory.


Backfire in intake


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

2)Boot between airflow sensor and throttle defective;
Will result in a lean mixture due to secondary air(false air)

3)Vacumm leaks;
Self explainatory.


Misfires

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

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

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


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 running engine.

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

3)Injectors restricted;
Do a test for delivery.If an injector is restricted,fuel delivery will be limited,thus power will suffer.


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 plunger will be limited.

4)Injector flow unequal;
Self explainatory.


Diesels(run on after shut off)

1)Airflow sensor sticking or binding;
The plate is not rising to position,continuing to deliver fuel.

2)Control plunger binding or sticking;
Remove the fuel distributor and ensure that the control plunger moves freely.

3)Injectors leaking;
Do an injector flow test and make sure that they seat correctly.Replace any that are defective.

4)Cold start injector leaking;
Remove and pressurize the system and replace if it leaks.


Fuel consumption high

1)Air-fuel ratio incorrect
2)Injectors leaking
3)Cold start injector leaking

Image

KE Jetronic

Plate adjustment;

1.Pressurize the system by removing the fuel pump relay and use a fused jumper wire with a 16 amp fuse between terminals 7 and 8.

2.There should be a gap of 0.002 inch all the way around the plate.Rest position should be 0.008 inch below the top edge of the narrowest part of the venturi.Free play should be 0.040 inch to 0.080 inch.If this does not occur,adjust until this measurement is achieved.

Potentiometer adjustment;

3200 to 4800 ohms of resistance between terminals 14 and 18 when the airflow sensor is at rest.

560 to 1060 ohms of resistance from terminals 14 and 17.

The reading should increase to 3760 to 5640 ohms when the plate is at its lowest point.Adjust until this is achieved.


Image

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ianaudia4
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Joined: Wed Apr 01, 2009 4:35 pm
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Re: potentially useful k-jet info

Postby ianaudia4 » Tue Jan 26, 2010 12:01 am

Fantastic, cheers.


1984 MK2 Havanna brown Storm
1989 MK2 Alpine white Scala injection
2006 Audi A4 3.0TDI quattro (the beast)


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