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: Rocking the Vehicle
WARNING Do not spin the wheels at more than 56 km/h (35 mph), and do not allow anyone to stand behind a wheel when pushing the vehicle: When the vehicle is stuck, spinning the wheels at high speed is dangerous. The spinning tire could overheat and explode. This could cause serious injuries. ...

Mazda 6 Service Manual: Precautions before welding
Vehicles have various electrical parts. To protect the parts from excessive current generated when welding, be sure to perform the following procedure. 1. Turn the ignition switch to the LOCK position. 2. Disconnect the battery cables. 3. Securely connect the welding machine to the ground nea ...