28-05-2012, 04:02 PM
Because at WOT with a gti6 inlet and throttle body, more air can pass through than the standard one... The ECU can't realise this increase in airflow, it doesn't have an airflow sensor - only an idealized table of what SHOULD be going in if the engine is standard...
Added to the fact the ECU knows how much air should get into the engine at a given throttle opening - since it knows the throttle position, so it looks up in it's table of how much air is going in and compensates with fuel accordingly... But it's not the same amount of air it once was because the inlet system has changed... So even at part throttle, it's incorrect.
The ECU is simply a dumb unit full of values that are pre-programmed... A Mass Air Flow sensor corrects this, but still, it has a working range, outside of this range it hasn't a clue what to do.
Added to the fact the ECU knows how much air should get into the engine at a given throttle opening - since it knows the throttle position, so it looks up in it's table of how much air is going in and compensates with fuel accordingly... But it's not the same amount of air it once was because the inlet system has changed... So even at part throttle, it's incorrect.
The ECU is simply a dumb unit full of values that are pre-programmed... A Mass Air Flow sensor corrects this, but still, it has a working range, outside of this range it hasn't a clue what to do.
