1989 k jet 16v gti....
i find my mixture goes out of ajustment fairly often
any ideas why ? everything looks in order, no obvious air leaks , fresh inj and o rings etc
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As with all k-jet systems,the basic mixture/co adjustment is made by turning a 3mm allen screw which effectively alters the height of the air vane flap in the metering unit. It is thus important that the air intake system , throttle butterfly,housing and air by-pass valve are clean and correctly set.Also check for split breather pipes.The mixture should be set on a gas analyser ,about 1.5-2% engine hot.hth
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If the airflow meter has a black plastic lid, prise this off if you dare, and gently wipe the carbon tracks which an arm sweeps across with a cotton swab and alcohol. It could be too late if the track is worn through. You can also ajust the tension of the spring here, mark it first with tippex or pen and jump it a tooth richer or leaner.
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I think you must be thinking about L Jetronic Ashok - this is K jetronic, which is entirely mechanical, there isn't any potentiometer track connected to the air flap.
As well as the possibilities mentioned by elekie & a/c doctor above, it could also be;
Fuel pump struggling to provide enough output
Fuel pump electrical supply poor
sticking air flap - this can be mechanical sticking, or sticking of the piston within the metering head - possibly muck in the fuel
if the warm up regulator has a vacuum connection, check itfor leaks
poor/intermittent electrical supply to the warm up regulator
leaks anywhere downstream of the air flap, including, as pointed out by elekie any parts of the throttle bypass valve (I forget the proper Bosch name for it, but I mean the small valve that opens to up the idle speed when the engine is cold)
It's also not entirely unknown for the cold start injector to leak, causing the mixture to zoom off to the rich end of the scale. For most of the time, disconnecting the fuel supply to the cold start injector and blocking it off isn't a bad step to take.
As a diagnostic step, it might be worth finding out what happens to cause the mixture to change. i.e., can you set it, rev the engine and get the mixture to come back to where you left it. Can you get the mixture to move about by wiggling various leads and pipes on the system?
Number_Cruncher
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im not aware of any air leaks ...would you agree a 2nd hand metering head would be worth a try?
its fairly consistant when working on it, meaning i can get the same results all day long, but after a few weeks it will go out by quite a bit....it goes out both ways , last time it was very waek causing a flat spot
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>>...would you agree a 2nd hand metering head would be worth a try?
If you have one in the corner of your garage, gathering dust, and it won't cost you anything to try, then, why not? However, these units are quite simple, and usually quite reliable, and I wouldn't rush out and buy one without being sure that it would fix the fault.
It's usually worth getting access to a pressure gauge to do any meaningful diagnosis on K-Jetronic systems - can you get your hands one one via a Golf car club or similar?
Number_Cruncher
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yeah i do have one laying around in the garage....
i also have the pressure gauges, as far as i can tell its the idle mix going haywire, the off idle mixture seems constant
i guess the most obvious thing i can think of is that the flap isnt always seating back in the same postion eveytime
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>>i also have the pressure gauges...
Excellent - what happens to the control pressure - does it vary when the mixture changes?
Number_Cruncher
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i never got chance to put the pressure gauges on it this time, it had gotten so weak it was nearly undrivable
i think i will put on the other metering head and set it up, then take it from there
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