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Do you really get 25% more power and 15% more economy?!

Clearly, they guy has stacks of positive feedback, so you can't be alone!

In my opinion, they're pure snake-oil. I've never yet seen one that backs up their claim with the kind of tests a major manufacturer has to do. I work in the car industry (though not in engine calibration) and I know the lengths a major manufacturer will go to in order to get a 5% improvement in fuel consumption / CO2 emissions (let alone 15%)! I see these guys offer the same box for pretty much any diesel too. I really struggle to believe that ALL the car manufacturers have managed to overlook such a simple way of making three times that saving!
 

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i dont have any experience in tuning xtrails (although i am interested in chipping my 55 dci), but i do have experience with landrover diesel tuning.
the majority of manufacturers do follow the same principle though,

landrover expect their vehicles to be sold all over the world and have to cope with varying levels of diesel quality. eg european diesel is much higher cetane rating than russia, same applies to water and particulate content in the diesel.
Because of this, they tune the vehicles to cope with the lowest common denominator with fuel quality, whilst still maintaining emissions levels that comply with the most stringent markets (think of California for instance!) and also maintain reliability with minimal dealer facilities (back end of australia or africa, russia etc). They also want to factor in fuel consumption and engine power too, so its all a massive compromise!

therefore most ECU driven diesels are very conservatively tuned.
As an example, the TD5 diesel in the landrover discovery produces 130bhp in standard form. Do a very simple remap and you can easily get 160/170bhp with no other modifications! Uprate the intercooler and a few other tweaks and you can get a reliable 200bhp. Although when i did my wifes discovery, i found cheap supermarket diesel made it run a bit lumpy, used quality BP or Shell and it flew! Fuel economy also increased by about 10% purely because the engine was utilising the better quality fuel more efficiently.
So dont write off ecu tuning on diesels as snake oil without first considering the market that the vehicle is sold in.

Nick
 

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That's a line I've heard before, but I'm not sure there's much in it. I know that the manufacturers we deal with at work tend to have different ECUs for different markets (for the reason you cite) but all the EC vehicles would have the same settings. They'll have "Federal" spec ones for the USA (except California, which will have different ones again) and probably different ones for Latin America and the Far East etc. In any case many cars are now smart enough to sense fuel quality and adjust their map accordingly. If the manufacturers of the various chips and boxes would post up official fuel consumption and CO2 emissions figures using the same test protocol as the major manufacturers have to use when quoting theirs (Directive 80/1268/EC), and carried out independently at an accredited test lab, I'd have a bit more faith in the figures.

Note that I'm not denying the possibility of getting more power - that's regularly done and very easy to prove, (especially with forced-induction engines), but as far as improved consumption and emissions go, I've not really seen anyone manage all three. The original vehicle manufacturer will also have to consider the warranty for the whole vehicle (not just engine, but driveline, brakes, suspension etc) at the increased power too. They do it themselves in many cases. A lot of PSA and Mercedes vehicles have the same engine in their range with different power outputs. That's usually just a "chip" too (although they know how to charge for it)!
 

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The plug in tuning boxes work by intercepting the signal from the fuel rail pressure sensor and lying to the ecu to tell it the pressure is lower than it really is. the ecu sees this falsified signal and responds by telling the diesel pump to pump harder. this results in increased rail pressure so for the same injector duration you get more fuel into the engine, hence more power. The mpg claims are partially false, partially true. Slightly better mpg comes from better fuel atomisation and from the fact that the increased torque can allow a careful driver to pull a higher gear so the engine is turning over at a lower rpm which allows more time for the piston to extract as much energy from each ignition stroke as possible before the exhaust stroke begins. Part of the mpg claim is when people go by the cars mpg gauge, the ecu thinks its squirted less fuel than it really has so the mpg readout is a lie because the ecu has been lied to.
The downside to these boxes is they are quite a blunt instrument. A good remap will only raise pressure slightly and will keep a close eye on what the pressure really is. It will get more fuel in by adjusting injector timings, reducing egr, increasing boost etc. A tuning box means the ecu doesn't know what the fuel pressure really is and because it is the only way it adjusts the fuelling the pressure usually ends up so high as to put undue strain on the pump and injectors, and things like the overpressure safety cutout will be inoperative, normally in a severe overpressure situation the ecu will cut the engine straight away to prevent damage, because the ecu cant see the real pressure you lose this safety feature.

If you want to build a tuning box you can, it's only about £5 worth of components, you can either use 2 opamps and tune the gains and offset to suit or you can be fancy and use a pic or uC with an analogue i/o and you can write some fancy maps that way.
 
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