When you go WOT the ECU then runs on set programmes (maps) that the ECU holds.
The readings from the O2 sensor is disregarded therefore the engine could be running too lean or too rich.
If you have a heavily modified motor then it would possibly pay to go to a after market ECU that can be adjusted and set up for your engine.
With the V6's and their VRIS inlet manifold valves you may have to take them out or set them open as I do not think the aftermarket ECU's can be programmed for them.
I installed a air/fuel ratio meter that takes readings from the O2 sensor and that has proven to be very accurate and helpful sorting out issues.
Otherwise go to a good shop with Dyno and get it checked.
|