Regardless of the make of diesel tuning box, they all start at the same point, namely increasing the amount of fuel injected into the engine.
Most diesel tuning boxes achieve this by increasing the fuel rail pressure and they do this by sending a signal to the car’s ECU which makes it believe fuel pressure is lower than reality. The ECUs then compensates by increasing the fuel pressure.
A small minority of diesel tuning boxes increase the amount of fuel injected by taking direct control of the injectors. They increase in the duty cycle of the diesel injectors. These type of diesel tuning boxes tend to be more expensive because of the hardware they need and because their wiring harnesses will be more complex.
This fundamental aspect of diesel tuning boxes however, depending on the price and complexity different tuning boxes will go further. For example some tuning boxes will also intercept the boost pressure sensor signals and after this the MAF sensor also. Beyond this there are tuning boxes will intercept even more sensors.
As a rule, the more sensors a diesel tuning box intercepts the more expensive they will be.
Are the expensive diesel tuning boxes worth the extra money?
You really have the weigh up the extra costs vs the extra power.
Which brings us onto the subject of the quoted power gains give by the tuning box manufacturers
Can you believe the figures quoted?
Generally, not really. Some manufacturers have their product tested independently (which gives low figures), other companies test in house and quote the maximum power gains. These gains could be the peak horsepower or they could be the peak gain ie where the difference between the standard engine and the chipped engine is biggest
So how can you choose a diesel tuning box?
Rule one. Ignore the power gains given by the manufacturer.
Two. Choose a tuning box which is adjustable. The more setting the better. Bur bear in mind the more setting a tuning box has the more work it requires by the user to find the optimum settings for their car.
Three. TUV approval is a bonus.
Generally speaking a quality tuning box with a lot of adjustment is going to give you the same kind of power levels as any other adjustable tuning box. Again, ignore the power gain figures.
And lastly, choose a company that you like or better still, go on a forum and see what people with the same car as you are using.