Mazda 6 Service Manual: No.4 hard to start/long crank/erratic start/erratic crank

No.3 will not crank

No.5 engine stalls-after start/at idle

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: Fuel line pressure inspection
Warning Fuel line spills and leakage are dangerous. Fuel can ignite and cause serious injuries or death. Fuel can also irritate skin and eyes. To prevent this, always complete the BEFORE REPAIR PROCEDURE. (See BEFORE REPAIR PROCEDURE.) Caution Disconnecting/connecting the quick r ...