Originally Posted by Pud237
Dump valve won't work on a JTD, cause there is no throttle to close. On a turbo petrol, coming off the accelerator closes the throttle butterfly, allowing a build up of pressure outside the inlet manifold for the valve to then 'dump' in a big hiss.
On a JTD (or any TDi) there is no throttle butterfly, so any boost the turbo creates when you come off the acclerator just goes straight through the engine, only no fuel is injected.
I think this might have been one of the first things I asked when I bought my JTD
the 140 has a butterfly which closes via the vacuum box thingy at the back of the engine, it is used in conjunction with the EGR system.
Capping off the EGR and leaving the vacuum connected to the butterfly may cause a build up of pressure one side, but engine side it will try sucking from somewhere - perhaps oil through the valve stem oil seels? (not good)
I thought these dump valves came free with chav baseball caps, exhaust tail pipes the size of paint tins, blue LED's you stick on your washer jets or fake leather(ette) seat covers.