I think a question a lot of people have with turbo petrol cars is this. If ECU tuning box changes the boost pressure and the car’s ECU does not know the real boost pressure, how can AFRs (Fuel mixtures) be correct? And if AFRs are not correct is my engine safe?
Its a valid question.
An ECU tuning box for a turbo petrol engine raises the boost pressure by making the car’s factory ECU think the boost pressure is lower than reality.
More boost equals more air entering the engine.
The air fuel mixtures are still correct, even though the ECU does not know the real boost pressure because the car’s ECU does not use the boost pressure signal to determine how much fuel should be entered in the engine.
The mass majority of modern cars will use the MAF sensor to calculate the fuelling and depending on the engine, also the wideband lambda sensor.
Even though the ECU does not know the boost pressure with an ECU tuning box, it does know amount of air entering the engine and it does know the RPM of the engine, with this information the car’s ECU can inject the correct amount of fuel into the engine.
There is a limit ie an ECU tuning box cannot raise the boost to whatever it wants. The software maps in the car’s ECU will have a table which says for X RPM and X MAF signal the boost must be between X & Y if the engine is operating correctly, if the MAF signal does not match with the MAP sensor range, the ECU will throw a check and possible put the car into Limp Mode.
ECU Tuning Box – In summary
Even though the car’s ECU does not know the real boost pressure, it does know how much air entering the engine and with this information it can inject the correct amount of fuel into the engine and this is what keeps the AFRs correct.
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