Good stuff, glad I stayed in playing with cars
How were you using the camera? all the photos I looked at were 1/800th of a second shutter speed but the aperture was changing, so I assume you were using shutter priority? No matter what you do, you can't leave things the same or trust the camera when you get on a track like CML. The black Astro turf and dark trees in the background fool the exposure and send it all over the place.
If you were using shutter priority and the lens needed more light (you say they are too dark) then theres not really anywhere for the camera to go because of the slow aperture on the lens. That's why I use Aperture priority - you'll always get a shot because the camera can always slow the shutter some more, and 1/800 is pretty quick. But like I said before, a track like CML I found full manual to be the best way to stop the dark areas messing it up.