Nissan Pulsar 2003: Ignition problems

Been having ignition problems with my Nissan Pulsar 2003. Took the car to the mechanic’s after the check engine light came on. If the car starts the first time it's great, but if it doesn't I don't bother trying after the first fail. Had all number of sensors changed and still have this problem. Mechanic has gone through car but can't find ignition fault.