I sometimes take my car to the track. I use a data logging program to time my laps and monitor certain engine parameters including maximum throttle position over the course of a lap. I have noticed that the reported throttle position is always exactly 84% or on occasion, 83%. I can assure you that over the course of a lap, I am hammering it. Why isn’t the max throttle position 100%? The throttle body is clear and operating as it should be. The car doesn’t seem down on power and there are no check engine lights. The air filter is not brand new but it looks clean. The program records all the other data channels exactly as I would expect it to. For example, speed, coolant temperature, etc. all look as they should.
For the record, the software I used is Race Chrono Pro installed on a Moto G (something) with a cheap generic Bluetooth OBDII reader.
To see if it was a car problem or a software problem, I also tried to used the OBDII reader on another car and with a different program (Torque Pro) on the street. I floored it a bunch of times and held it there for a few seconds each time. That resulted in a throttle position no higher than 88%. Torque Pro was recording throttle position once per second. The air filter on that car is filthy.
What gives? How does the OBDII determine throttle position? Why isn’t it reporting 100% throttle opening?