Another question for penak or anyone else who feels qualified to answer.. If a tuning box works mainly by increasing the injection of fuel how can Shambles and others who have used a tuning box been able to report an improvement in fuel economy?
Withouth REALLY careful methodology, fuel consumption measurement is truly hard. Mostly placebo effect I would say.
When you install a device that is supposed to decrease fuel consumption, you usually tend to get such results. Human mind is so sensitive to suggestion. What probably happens is that the driver subconsciously drives smoother, and errors in fuel consumption measurement do the rest.
It is a simple physical truth that you cannot modify a modern diesel in a way that would result in even 1% better fuel economy. These engines operate already so close to their theoretical maximum. If such result was possible easily, the manufacturer would already have done it. Increasing power is another thing, that may happen, but engine's thermodynamical efficiency cannot be measurably enhanced.
If the box varies the torque curve, it is however borderline plausible that in certain conditions you could keep the engine closer to it's optimum rpm by being able to use larger gear than previously. But that would be valid only for a very narrow set of conditions that should not be noticeable in a normal traffic cycle.
There is a funny story from here (Finland) of how deceivable even car journalists can be. One of the local tabloid papers published a story on their car pages about a total scam product, a stainless steel bar that is simply dropped to fuel tank or attached to fuel line with cable clamps. According to the manufacturer that steel bar has been impregnated with "cosmic energy" and will change the molecular structure of the fuel to a more efficient form. In other words, full bore baloney...
The poor journalist was dumb enough to swallow that garbage, apparently hook, line, and sinker. He drove from Helsinki to Rovaniemi withouth the bar in tank, dropped the bar to the tank and drove back, and found out that he had used less fuel. The poor sod reported that as the effect of the cosmic bar in his article withouth stopping to think OTHER more plausible explanations. The scream laughter that erupted on the paper's net forum was humiliating to the reporter, to put it mildly...
BTW. I have a nagging suspicion that many of those "tuning boxes" dont actually change anything else than just the response curve of the throttle pedal. Some results here say that the box don't seem to have noticeable effect on fifth gear, which would fit to that theory.
The boxes even having TUV approval also indirectly point to that direction. TUV approval does not evaluate the truthness of manufacturers power increase or economy claims, it just guarantees that the accessory is not dangerous in traffic, which fits a do-nothing-box marvelously.
Many shady firms use TUV approval as validators of their products in their marketing, when in real life the approval only says "This is not dangerous to be used in traffic".
It is a bit like using manufacturers ISO 9000 certification as an indicator of consumer product quality. A company that makes solid cast iron life buoys can have ISO 9000 certification...
