Proper tuning boxes made by the likes of Steinbauer are somewhat more pricey than this, and they don't just plug into the fuel rail, they take a feed from the throttle position too...not as i'm recommending them as such.

Can't quite get me head round an increase of 20% just plugging in to the fuel line, how does the magic box know how much throttle is being applied, revs etc.

When you read the text for these cheap things (which used to be about £12 a few years ago) they tell you absolutely zilch how it works.

If these boxes can actually give more power for less fuel, the Laws of Physics are being defied. So the inventors have proved Scotty of the starship Enterprise wrong in his beliefs.

Proper tuning boxes can have their place, i had a pre d4d Avensis Diesel, it was superb trouble free car but lacked power, and i mean as frustrating as anything i've driven.

Toyotas are difficult if not impossible to get remapped, so a tuning box would have been the only thing, when it was cold the pump must have richened up slightly and it pulled better than when warm when it became sluggish...if i had my time again i would have experimented with a better box such as a Steinbauer and probably kept it long term, it didn't need a 20% gain just the equivalent of the quarter trun on the fuelling screw we used to do with Bosch mechanical Diesel pumps would have been enough.

When i advertised it, Indian taxi drivers beat a path to our door and it wnet off to Aylesbury to be a mini cab.

Most of these cheapo tuning boxes are a box containing a couple of electronic bits and an LED to make them look clever. In truth all they do is convince the engine its still cold and needs more fuel and in a diesel more fuel means more power. It certainly does not mean better economy.

More fuel also means more smoke or particles and in a modern diesel with a DPF they will clog up quicker and potentially cost up to £1000 to replace.

If you want a quicker car buy a quicker car.