No. Eating grass usually does the opposite by bulking up the stool. Many cats enjoy a good bit of grass every now and then. Every single cat of the 100's that I have known in my life will eat grass. Some vomit it back up - using it as a natural hairball remedy. Most just use it as a colon cleanser.
Petsmart and other pet oriented super stores have even started carrying grow it yourself wheat and barley grass kits. I reccommend these over outside grass since the grasses will be pesticide and weed free and contain only plant types that are non-toxic to cats. If you have a "grass freak"
you might want to investigate keeping a couple of kits growing year round. There easy and will make your cat happy.
Kramer may be getting into a type of grass that does irritate his digestive system. He might be getting a dose of pesticides or herbacide that can cause not only loose stools but long term helf affects. Eating outside grass can also bring Kramer into contact with a variety of bacteria and pesticides. Indoor pet store grasses may divert him from the outside kind so that he can continue to explore the outside while leashed
If your cat is experiencing loose stools right now look for dietary causes first (including the outside grass) then move on to parasites and diseases. Make sure 'Special K' doesn't become dehydrated.
Hope this clears up soon.