The internet forums are full of this subject, some sports drivers (wannabe) are enthusiastic. Even the fuel consumption is supposed to be lower. Difficult to believe, but we'll see. Perhaps a few irrefutable facts will help to clear the matter up.
The Diesel engine, as modern as it may be, is still a self-ignitor with quality regulation. I.e. if somehow there is a surplus of air, a larger injection amount will give out more performance. In the meantime however, through the comprehensive use of turbo-charging, there is more than enough air available.
There are three possible ways to chip-tune an engine:
1. A sensor signal is manipulated, before it reaches the control device. 2. One or more sensor- or actuator signals are altered. 3. The characteristic map is directly addressed.
1. This here is an often used example, namely the altering of the signal from the accelerator pedal, possibly even split into various modes. In this case one gets the least value for one's money, since logically speaking, all the control device can do here, is to simulate a light, a stronger or a very hard pressure on the gas pedal.
Now, you may justifiably argue, that all one needs to do is to press harder on the pedal, to achieve the same effect. Indeed, the electronics are apparently a little faster and can present a more spontaneous engine through giving a lot a gas and the reducing it again at the right time, how that's going to save fuel, remains a mystery.
2. Here, it gets down to business, then e.g., through reading out and the respective raising of the rail-pressure, a torque can be produced, such as one cannot achieve just by changing the accelerator position. In this case, one should, in contrast to the 1st solution, not go for the cheapest possible product. Otherwise, the tuning of a Diesel engine through raising the injection amount, is as old as the hills.
Here one can, for the first time, really speak of a performance increase, which at the end of the day, leads to an MOT-visit and which e.g., can attract the attention of the car-rental companies. In this case, even long after the vehicle has been returned, can it come to effective law-suits. This is likely, particularly if one has boasted in the respective forums about what one has done.
As always at this point, one has to ask, if these measures are such a stroke of genius why don't the manufacturers use this possibility themselves. We've already said enough about this subject in the previous article. Here is simply a comment, of course there is a certain amount of variation in any series. The manufacturers are bound to a strict type-test which includes a long-term test, e.g., over 80.000 km, the tuning companies don't have any such regulation.
3. If at all, we would advise an alteration of the characteristics map for the particular vehicle, indeed, not if it's already the strongest model in the range. If a 2-liter Diesel is being offered with a 100, a 125 and a 150 kW engine, the two weaker engines would be more suitable for tuning. Perhaps their differences are only to found in the software anyhow, then any tuning measures could in fact, backfire on you.
In addition, should the tuner maintain, that he has installed an adaptive device, then all that's been done, is a manipulation of the control device. For any other intervention, it must be documented that an alteration, through the BUS-cable or an interface, has taken place regarding the individual sensors. If no information is given, nothing can be learned. A tuner who has done a before- and after performance test, and can supply the respective documents, has probably done his job properly. 12/14