Ok, I know a change occurs at 3800 or so rpm, the secondary injectors come on and the computer reverts to it's pre-set fuel maps or something? I assume there's a sensor or 2 that doesn't get used past 3800rpm?? I'm just wanting things to check for my shoddy hesitating low in the rev range...

Charlie

 

below 3800 the car is running on what it knows from sensor data.

above that, its running on internal fuel maps.

check the codes in the ecu.
what trouble codes does it have?