I'm thinking about replacing my fuel pump and injectors in the near future. If I upgrade to a walbro 255 and the xjr6 bigger injectors in my na car would I need to get a new ecu or find some way of tuning? I'm not trying to add a lot of hp but if I'm gonna replace something I figure I might as well try to upgrade it anyway.

 

The power of the engine is limited to the maps or data arrays in the stock ECU

The o2 sensors determain the output gasses to make the ECU calculate the amount of fuel to inject into the cylinders

The ECU has a " target " left over O2 level after cylinder combustion that is different then a optimal fuel/air ratio for the other combustion gasses like nitrates

This is called short term fuel trim and the ECU constantly adjust the cylinder fuel charge * pulsewidth or time ) to maintain this target and is assigned the value of 0.0

By putting in a higher capacity fuel pump or injectors the ECU will adjust the injectors pulsewitth to put out your original power and not go to a rich mixture ( positive STFT )

If you increase the mass air flow into the cylinders the ECU will adjust up to a certain design point ​​​​​​a new pulsewidth for a larger fuel charge into the cylinders .

You can extract more mechanical power ( work ) from the expanding cylinder combustion gasses in the present setup with a Andy Bracket which biases the ignition timing before top dead center