Can too much caffeine dilate your pupils?

Yes it can - Caffeine is a stimulant and causes a release of adrenaline.

Adrenaline is the hormone which prepares us for 'fight or flight' in stressful situations and it has a number of effects on the body. One of these effects is dilated pupils (if you are going to fight or run away from danger, you will need to be able to see as well as possible!)