But the ECU knows how much fuel is being used as the tuning box is telling it how much fuel to inject.(well,in a sense). Tuning boxes are only really kidding the engine through fooling the ECU (by saying its cold outside,increase fuel).
So therefore,the ECU knows how much fuel's being injected(but doesnt know its actually a lot warmer than the tuning-box is telling it).
Thats why tuning-boxes arent good in long-run for fuel-pumps,injectors,cylinders,turbo's etc,as the engines running too rich.
Getting more torque thru lying to the ecu,i get,but is the extra mpg/torque worth it at the expense of the engine going through quite a fair bit of 'over-everything'.
Thats why a remap on a some cars(where the turbo boost isnt physically able to be increased) isn't the brightest idea for engines. The cylinders run hotter,so does virtually everything else(and richer);as they still have the same amount of boost from turbo(as its non-adjustable), but increased fuel input.
Im terrible at remembering things & have forgotton where i was goin with this lol
Mostly, this is nonsense - or little bits of information about completely different types of tuning boxes and forum "rumours" mixed together
Tuning box type # 1 - IAT tuning box The signal from the Intake Air Temprature sensor is modified so that the ECU "thinks" it is cold, (or colder than it is) and makes the engine run richer, simple/ works well (to an extent) with early petrol NA or turbocharged non cat cars, can contaminate cats on modern petrol cars with cats, works on diesels/ turbodiesels but there are better techniques - this is the only type of box where temprature is part of the control (ie - "its cold outside - increase fuel") - this may be a resistor of the correct value
Tuning box type # 2 Diesel common rail pressure boost type tuning box - Connects between the common rail pressure sensor and ECU, increases fuel pressure by modifiing the sensor signal so it reads LOWER than it actually is, ECU automatically compensates, so a larger amount of fuel is injected per cycle, exept the ECU "thinks" the same amount of fuel was injected as before the tuning box was added
Tuning box type #3 MAF sensor type- In a nutshell the MAF sensor measures the amount of air going into the engine, although it may be pressure and temprature compensated its function is to measure the amount of air (Mass Air Flow) -
(turbo-diesel)The tuning box connects between the MAF sensor and the ECU, the signal is modified so that the MAF is measuring more air than it actually is, the ECU squirts more diesel in to compensate, this can produce a with a significant power and torque gain as the extra fuel boosts the energy in the turbine, which has a knock-on effect on the compressor, although peak boost pressure is controlled by the actuator (so the absolute peak boost pressure is theoretically the same as before) the boost comes in sooner, and the turbo spools quicker, with more boost across the entire powerband >>so the boost is changed INDIRECTLY with this type of tuning box.
Tuning box type #4 - Digital microprossesor multi channel programmable tuning box with multiple maps and direct control of the electronic actuator. the title says it all really, this is a realatively sophisticated box, effectively a second ECU, takes over several sensor signals, etc this type has direct control of the turbo boost pressure, (engines with electronic actuators, obviously)
There are many different variations of these, including, "passive" resistor boxes, active analog boxes, digital, digital programmable with multiple maps, multi- channel digital etc etc
My (turbodiesel) car runs very cool (about 75degrees) if it ran hotter i would be happier (and i would get a better MPG too, apparently)
There is a school of thought that says increasing the power+ torque of an engine (ie- fitting a tuning box) REDUCES the stress on the engine, as it does not have to be worked so hard, to achieve the same result