FWIW, unless you're doing this on a frequent basis, you don't have much to worry about. If you're using a couple days a month, hitting that 4g level isn't going to kill you. If you're using daily, then it's a big problem.
The problem is the frequency of the high dose. Your liver will have no problem bouncing back from a few days of 4 or even 6 grams in a day, so long as you're not doing it over and over and over. I think I drew the limit at 7g twice per month. My liver is fine, but I only did that for a few months. Had I pushed it longer, that would have been damaging, I've no doubt.