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Tuning Boxes – How Do They Work?

Example wiring loom for tuning box

Image from DTE Systems.

Tuning boxes are a plug-and-play power adder.

In their simplest form, a tuning box is a signal manipulator. They connect to the relevant sensors on the engine, manipulate that signal and send the new signal to the car’s ECU.

What sensors do tuning boxes manipulate?

Diesel Tuning Boxes

On diesel engines at a minimum, tuning boxes will manipulate the signal coming from the fuel rail pressure sensor. To make more power on a diesel engine we want to increase the amount of fuel being injected into the engine.

To inject more fuel a tuning box reduces the sensor signal going to the car’s ECU. This makes the car’s ECU believe fuel pressure is lower than it actually is, the ECU in turn increases fuel pressure up to the level it should be. End result, the engine injects more fuel into the engine.

On some cars this is not enough

Either manipulating the fuel pressure sensor is not enough to get the engine’s ECU to increase fuel flow into the engine or adjusting the fuel pressure only leaves a lot of extra power in the engine.

Whatever the case, on some engines the MAP sensor signal/s are also manipulated. Again, a tuning box will tell the engine’s ECU that boost is lower than reality forcing the engine’s ECU to compensate by increasing boost pressure.

Going one step further, on more advanced tuned boxes, the tuning box may also tap into an engine position sensor ie camshaft or crankshaft. This gives the tuning box more control over the fueling (and boost pressure if applicable)

That is diesel tuning with a tuning box.

What about petrol engine tuning boxes?

Until recently, tuning boxes on petrol engines where a complete no no. The reason being engine ECU’s and knock sensors were not advanced enough.

In recent years modern petrol engine ECU’s can constantly adjusting ignition timing to get the best possible fuel economy and engine power for the quality of fuel that the engine is consuming at that moment in time.

These modern ECUs can adjust engine timing so much that they can deliberately advance ignition until it starts to induce knock/detonation and the knock sensors and associated software are so fast and so sensitive that the car’s ECU can retard ignition timing so quickly that the the engine will not get damaged.

And this is the technology that tuning boxes rely on to be safe on turbo petrol engines.

Tuning boxes on modern turbo petrol engines work primarily by manipulating the MAP (Manifold Absolute Pressure) sensor signal going to the ECU. Like diesel tuning, the tuning box reduces this signal making the car’s ECU think the boost pressure is lower than reality. The car’s ECU then adapts increasing boost pressure to what it thinks is normal but which in fact is higher. This is how a tuning box gets an engine’s ECU to increase boost pressure.

On some cars, this is as much as you can do. On other cars adjusting the MAF sensor signal as well as the MAP sensor/s signal can release even more power. Again, with the MAF (Mass Air Flow) sensor, the tuning box reduces the signal going to the car’s ECU. And with even more advanced turbo petrol tuning boxes the engine position sensor may also be tapped in to so the tuning box can vary the signal manipulation according to RPM.

Increasing boost pressure increase engine power but it also makes the engine knock/detonate sooner, to stop engine damage tuning boxes 100% rely on the car’s original ECU to keep the engine safe.

Tuning Boxes in Summary

Tuning boxes work by manipulating the signals going to the car’s ECU. By reducing the signal we can get the car’s ECU to compensate in a way that increases engine power. Primarily by increasing fuel on a turbo diesel engine and by increasing boost pressure on a turbo petrol engine.

Diesel Tuning Boxes manipulate the following sensors in this order

Fuel rail pressure sensor

MAP sensor (if applicable)

Petrol tuning boxes manipulate the following sensors in this order

MAP sensor

MAF sensor (if applicable)

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This page was last modified Oct 30, 2019 @ 7:31 pm

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