There is a type of injector set up on most K-Jetronic fuelled VW engine's be that 16v or 8v.
The air shrouding system was implemented to maintain emissions at low engine speed when the engine's intake of inducted air it at it's lowest.
How the system works is pretty simple in its design:
The injector is the same type of injector as the non shrouded variety but with the edition of a "top hat" on the end of the injector, this top hat allows air to pass through in the small gap between the injector body and the top hat itself, the air is then diverted either left or right (can go both ways) and is expelled outwards shrouding the fuel that is being injected.
The purpose behind this air shrouding is to enable the injected fuel to mix with the shrouded air providing better atomization taking the fuel from large uneven droplets to a finer mist, this allows the fuel to mix with the incoming inducted air far better that it would have leading to a faster and even burn rate which delivers a strong power stroke.
With limited inducted air at low rpm conditions its essential for the fuel to mix with that air as best as it can to allow all the fuel to be burnt during the combustion process, if its not all burnt it leaves in the exhaust stream which leads to high emissions.
The system parts
- Fuel Injector P/N: 043 750 2043b
- Lower injector insert P/N: 035 133 554
- Lower Insert seal P/N: 035 133 557
- Injector seat (Brass) P/N: 034 133 555a
- Top injector seal P/N: 034 133 557e
- Lower injector seal P/N: 035 133 557a
System air flow
The air that is used for the air shrouding is drawn from the upper filtered part of the air box via a rubber hose that connects to the crank case breather, this hose has a smaller section the tee's off and connects to the lower part of the inlet manifold. The engines induction stroke draws air in as normal via the throttle body and through the above mention hose into a cavity that runs along the inlet manifold, the air then fills the orifice surrounding the injector body then out through the injector top hat.
There are two issues that arise with this system over time.
-The top hat becomes blocked as it only has approx. .3mm gap between the injector body and injector top hat, as you can imagine a few dirty air filters will allow this to be come blocked.
-The lower insert can fail, as it's made from plastic it will degrade over time and become brittle and very easy to damage when changing the injector seals.
The issues either of these faults cause are ruff running of the engine most noticeable at lower rpm, this is due to either an excess of air from a damaged insert which will cause a lean mixture in that cylinder or a poor burn rate of the fuel due to having no air shrouding.
Advice.
- If your going to overhaul this set up get all the parts first and set to work, its not a hard job but to limited damaged removal of the inlet manifold is necessary to allow the old lower inserts to be removed without debris falling into the engine.
Below is a link to my YouTube channel where I have run through the above system, I always believe that to understand something you need to firstly know the theory and then get hands on and actually see the parts so hopefully the video will assist in the understanding and overhauling of the system.
Thanks
https://youtu.be/yMR1qV081k4