This may not be the answer to your problem, but I had a fuel related problem with my 306 2.0l hdi that caused problems for a year. Many times did I call the AA eventually it started each time after perhaps an hour or 24 hours.
I changed fuel transfer pump, fuel relays and spent a fortune. Then a AA man found the problem that cost nothing to fix.
The problem was a contact in a multi-way plug and socket that is under the left front wing. This plug takes part of the engine wiring loom onto the engine. It is low down and difficult to see but you will find it if you look.
There are two big multi-way plugs. Aircraft type with screw-ring securing devices to keep the water out.
Take out the larger of the two plugs and examin the pins. One pin in the centre of the group was brown, the remained dull silver. I cleaned it up with sandpaper and electro-lube contact cleaner then with pliers twisted it very slightly to get better contact with the femail scoket and put it back together. Bingo! never been a day's problem since. Don't twist the pin first time round. Just see if the car will start. If so you man not want to bend the pin. If you do then only do it a tiny amount or you will wreck the connector. Incidently the securing ring may be hard to get off but you could try a chain wrench, or wear a rubber glove.
306Man
February 2012
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.