It's really hard work at first, I sympathise. My boy, Indie, used to poo in his crate and get into a right state whenever we left him, but I can say with total certainty, the only thing that made it better was leaving him more.
I don't know if you are doing what I did, but I was there ALL the time, and never left him on his own at all really. It sounds weird but it's even more difficult for them if you are there so much then not.
4 hours is a long time, I'd say he's too wee to cope with that - my ten month old can only now cope with 4 hrs at a time.
Persevere, he'll get better I promise, it's like training toddlers, just hard slog.
Shona x