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I'm sure others will ask, as it often helps people to help you, what engine variant you have and how old, how many miles etc. The more information you can provide the more people can help.
I wonder if the "loss of power" is in fact your van going into limp mode?
What code reader are you using? If the glow plug light is flashing I'd expect a fault code, though other more knowledgeable members may correct me.