These Ebay diesel tuning boxes

It depends on who is selling them. A lot either jigger the output from the lambda sensor or fiddle the mass air flow sensor outputs.

Not big, not clever in many cases.

Someone use to seel something similar for Jags for a silly price £200 or so, and inside an impressive looking box with flashing LEDs and complicated looking connectors was a wire wound resistor to be wired into the autobox to change the shift points. Not that they told you what was in the box, just "attach wire 'A' here, wire 'B' here.

Yes. They trick the ECU one way or the other. Cheap, cheerful tuning for the masses.

If you buy yourself a VAG TDI, you can have mine, for the cost of postage.

It does sod all on the 16v PD engines.

It depends on the box, what they do. The simplest just bump the fuelling up a bit, yes.

However, JackH reckons they work on older generation engines.

Yeah, you're right- they do. Not as well as a remap or a better box, but they work. The very cheap ones are a resistor and a wiring harness- the same mod can be found on

Works fine on the Fabia - lots more lower down torque, minimal increase in smoke when floored.

Worked ok but not as impressively, on the 115 PD Mk4 Golf I recently had.

-- JackH