It is an attempt to approach the diesel engine in terms of consumption after the switch to direct injection has already taken place. The result is such an elaborate juggernaut that the workshops can hardly master it afterwards. The initial idea was actually quite simple and plausible. We will now pick out one of the more complicated constructions.

It must be clear, however, that the variant described here has nothing to do with engines that will later still be designated as 'FSI'. Fuel Stratified Injection stands for a lean mix concept from VW where an ignitable mixture with lambda = 1 or even somewhat lower is to form around the spark plug, what should be thinned out more and more with greater distance.

The goal is to save fuel and also of the formation of CO₂. So the direct injection into the combustion chamber is directed in such a way that it brings the main charge close to the spark plug. This can be done by direct targeting there or wall-guided, with the piston crown also representing a wall. The latter variant is probably the most common.

The part of the piston visible from above has the shape of a spherical surface, for example, for the purpose of directing incoming mixture or a cloud of fuel back upwards, the wall as the turning point. The generation of swirl, e.g. by flaps in the intake duct, is also very important. From their position you can also see in which area the whole system is actually effective.

No, you can't take full advantage of the engine power in this way. The system must then also be able to redirect if necessary. Because to suddenly rev up the engine, even a modern direct injection engine needs a certain enrichment of the mixture. As you can see, the FSI system is pretty pointless if the driver doesn't take part or if the driver is constantly using a lot of performance.

The location of the injector is of course also very important. It is not always placed in the top of the cylinder head next to the spark plug, but can even be located in the cylinder block below the intake duct (see picture above). The main thing is that with its 50 bar up to in those days after all 100 bar, it helps to ensure that the electrical system can ignite, which is so important.

It seems that there was no shortage of it, that the system did not suffer from it. The engine started and ran, but there is such an uncomfortable indicator light that, among other things, denies you access to a TÜV sticker during the emissions test, the Malfunction Indicator Light. It has probably indicated defects more often than in other internal combustion engines.

Why? Because the exhaust system turned out to be quite complicated due to the wonderfully simple idea. A transversely arranged four-cylinder does not have one exhaust pipe with a lambda probe before and after the catalytic converter, but rather two lines, as if it were a longitudinal V-engine with a broadband probe in front of and a two-point probe after the catalytic converter. But even that is not all.

Because, of course, the three-way catalytic converter does not get along very well with a mixture that is too lean overall. It prefers lambda = 1, because it feels comfortable there and works to satisfaction. So even with two catalytic converters, too much NO_X comes out in the end, which requires post-treatment by an additional and appropriately designed catalytic converter. And its work is then monitored by a NO_X sensor.

Did you count, a total of 5 probes, each of which in the workshop can easily cost over 200 euros including installation. And as if that wasn't enough, there are also problems with the control system or the flaps in the intake manifold itself. As I said, it is rare that the car completely stops, but engine misfires after restarting are not. In addition to these, which usually appear a little later, there was one more decisive factor.

Actually, it should save. It did as long as you drove very cautiously. Then experts took a closer look at the regulation of the flaps in the intake manifold. The result was that, of course, they only regulated in a certain speed range. If you translate it into motorway speed, so the at the recommended speed was long ago over there.