Fuel Injectors and Injector 'O' Ring Seals
Fuel injectors are one the causes of bad running and in particular bad starting when hot. After a few years they start to gum up and loose the correct spray pattern and will also leak into the cylinders after the engine has been shut off. There are several remedies to solve this problem, obviously a new set would be the answer however having them cleaned ultrasonically with injector cleaning fluid will remove most if not all the deposits and return the spray pattern to normal. The other is to use on a regular basis a fuel injector clean that goes into the fuel tank, some of these products are better than others. In the USA one of the best ones is called Techron and is made by the Chevron Oil Company, I have used this myself and can vouch for it's effectiveness.
The injectors themselves are only a push fit into the head and are held in place by rubber 'O'type sealing rings, after many years of getting ver y hot and then the rubber looses it's ability to seal and they go hard. This has the effect of pulling unwanted air into the cylinders causing the car to run lean and give poor performance. The only cure is to renew them. There is now available a new type of seal made out of a rubber compund called Viton, this apparently gives longer seal life. The other part that also needs to be replaced are the plastic holders that the injector sits in. this is screwed into the head and can be removed using a suitable sized allen key, be careful not to crack them as the bits will end up in the cylinders!
To replace the seals you first have to pull the injector out of the block, this is sometimes difficult to do with ordinary tools like pliers etc, there is however an injector pulling tool available from VAG that makes the job a whole lot easier. Once the injector is out of the head then remove the old seal and install the new one, pushing home the injector back into the block afterwards.
To test if your seals need replacing it is possible to use spray carb cleaner in an aerosol can. Witht the engine running spray a little on cleaner around the area of the injector where it goes into the head, if the idle alters at all then you know the cleaner has got into the cylinder and the seal is therefore defective.
Click to enlarge
cylinderhead with the injector holders
detailed photo of the injector holder
