My mates van (ldv pilot ex royal mail with about 35,000 miles) blows out white smoke/steam from the exhaust occasionally after changing gear. When the revs are lowish (just after changing) it judders, blows out white smoke, seems to sort itself out and then accelerate as expected. Anyone have any idea why this is? One garage says its the fuel pump.. which costs £600 + labour to replace Other suggestions have been that theres water in the fuel tank, or a leak in the fuel line. Might be buying into this van (work with the guy) so I'd prefer to know its not gonna cost a shed load to fix before I part with any money!