Just a couple of ideas, might not be useful (or coherent for that matter 
)
To my knowledge a loss of keycode should not interfere with the lp pump, the immobiliser merely shuts off the injectors.
I don't recall off the top of my hat wheter the 306 has a pressure sensor on the lp system (don't have my Haynes or Autodata handy atm), but with my HDi I can hear the lp pump whizzing whenever I turn on the ignition regardless of how many times I do that.
One really simple way of testing the lp system is to disconnect a fuel line under the bonnet (before or after the filter, just make sure not to get any crud into the lines), put the end in a container and see if fuel gets pumped through when you turn on the ignition or manually power the pump.
Might be a blockage of some sort, or maybe the lp pump is simply not getting enough fuel to the hp pump. Might even be water in the fuel filter (seems unlikely to me).
Just because the lp pump was replaced 2 years ago doesn't mean it can't be at fault (rule #1 of problem solving: don't rule anything out
)
Edit: also check the fuse for the lp pump, it's #35 under the bonnet iirc. You should also be able to feel the relays behind the ecu click when you turn on the ignition.
)To my knowledge a loss of keycode should not interfere with the lp pump, the immobiliser merely shuts off the injectors.
I don't recall off the top of my hat wheter the 306 has a pressure sensor on the lp system (don't have my Haynes or Autodata handy atm), but with my HDi I can hear the lp pump whizzing whenever I turn on the ignition regardless of how many times I do that.
One really simple way of testing the lp system is to disconnect a fuel line under the bonnet (before or after the filter, just make sure not to get any crud into the lines), put the end in a container and see if fuel gets pumped through when you turn on the ignition or manually power the pump.
Might be a blockage of some sort, or maybe the lp pump is simply not getting enough fuel to the hp pump. Might even be water in the fuel filter (seems unlikely to me).
Just because the lp pump was replaced 2 years ago doesn't mean it can't be at fault (rule #1 of problem solving: don't rule anything out
)Edit: also check the fuse for the lp pump, it's #35 under the bonnet iirc. You should also be able to feel the relays behind the ecu click when you turn on the ignition.