Hi Woz,
You are right in your theories and as for the advice so far given, they should be asking you for advice! Not you asking them
Closed loop is basically the ECU fuelling real time using data from the lambda sensor and adjusting the fuelling to match the correct AFR. Closed loop is used for idle running and part throttle with low load. The ECU may 'learn' in closed loop but it certainly doesn't learn in open loop.
Once the ECU senses enough load it will revert to open loop. In open loop the ECU runs from a preset map and is not adjusting AFR using real time data. It is using preset parameters and these parameters are based on you running the hardware it was originally mapped with. i.e 315cc injectors, stock MAF, turbo etc.
For example - If you are running 20% bigger injectors with a 315cc map, in open loop the car will be overfuelling by 20% until you reach the point where the old injectors would have hit 100% duty cycle. Only then will the bigger injectors be of any benefit. (Probably the reason it's cured your full boost misfire).
In short, for the car to run optimally you need to get it mapped. The mapper will change the injector scaling to suit which I am told isn't too complexed to carry out, although I am no expert whatsoever.
You may 'get away' with not mapping it for a while as it will be rich rather than lean, but what's the point in changing hardware if it means the car isn't running at it's optimum. Also, running too rich for prolonged use can result in bore wash over time.
Hope this helps,
Cheers, Mitch.
Bookmarks