The 'bolt-on' tuning boxes fool the ecu into believing the fuel pressure is low and simply put more fuel in. On turbo-charged cars that's not complemented by an measured increase in air from the turbo pressure being increased as the ECU thinks everything is as it should be. As a result, you'll likely get a cloud of black diesel smoke in your rear view, a clogged DPF if you have one, a catalytic converter full of soot and a clogged EGR valve. The box may only cost £70 but the resulting (damage is the wrong word) will cost you much more in the long rung. I will be using these in the very near future to remap my 2.2 X-Type - www.celtictuning.co.uk