We have just acquired a 36000 km 456 that has been sitting for some time and it exhibits the fault of going onto 6 sometimes. All it requires so far is to switch off and then restart whereby it goes back onto 12. We contacted the previous owner who replaced both pumps with new Bosch units. At this stage we have not removed and checked the pumps or the tank as I understand the new fuel can dissolve, or at least break down the rubber sleeve that suspends the pumps within their brackets. From the exhaust colour it seems it is consistently the left bank that has the fuel issue. Has anybody encountered this and dealt with it? I have replaced the relays too with correctly rated units as I am aware these really are a service item which should be replaced every 10 years. My money is still on the partially blocked, by rubber pieces, left hand fuel pump but my experience makes me doubt that as it is always able to perform properly once restarted for sometime. I also if it were rubber pieces blocking the pump for both pumps to be affected as they are side by side basically. Being an old bugger with an innate suspicion of the reliability of anything electronic I am wondering whether it may be electronic, such as a diode, or a dry solder joint within the ECU which is overheating. The relays certainly seemed to make it idle better but fear it was pure hope and imagination. Owing to other commitments (13 other classics and grand children) I haven`t given it a road test yet.