If your Glow Plug light (which looks like a coil of wire and is on the lower left side of the clocks) starts to flash then this means that the engine management system has logged a fault.
What you need to do is to take your van to a Ford Dealer, A good independent garage or fuel injection specialist, and ask them to read the fault codes. They will connect your van to their diagnostic computer system and read the fault codes, which will be a collection of numbers, these numbers are then used to determine the problem, Which may be one of hundreds of things, such as Fuel pump problems, Accelerator problems, egr valve problems to name but a few. Once you know the fault codes you can Repair the problem, or post the fault codes up onto the forum and someone will help you determine what is wrong