2001 Mercury Sable 2001Sable starting problems

Electrical problem
2001 Mercury Sable

My 2001 Sable starts up most of the time with no problem. But lately it will intermittently not start. It bucks for a few seconds and then cuts out. If I wait an hour or so, it will then start. The mechanic kept it for over a day and was able to start it many times. However, several days later, it would not start and I had to have it towed. Then it started working again with no problems. Mechanic says that it could be many things and can't fix until it breaks again.

I have read that the fuel pump could be the problem. I recently had my cam position sensor and synchronizer replaced. Battery checks out fine.