Mazda 6 Service Manual: No.5 engine stalls-after start/at idle

No.4 hard to start/long crank/erratic start/erratic crank

No.6 cranks normally but will not start

Other materials:

Mazda 6 Service Manual: Intermittent concern troubleshooting
  Vibration Method 1. If malfunction occurs or becomes worse while driving on a rough road or when engine is vibrating, perform the steps below. Note There are several reasons vehicle or engine vibration could cause an electrical malfunction. Some of the things to check for are: ...

Mazda 6 Service Manual: Split Folding
By lowering the rear seatbacks the luggage compartment space can be expanded. WARNING Do not drive the vehicle with occupants on folded down seatbacks or in the luggage compartment.  Putting occupants in the luggage compartment is dangerous because seat belts cannot be fastened which coul ...