EGR Blank - Vacuum pipe and air doser

[bradspau]

I am still investigating the cause of black smoke and poor MPG on my 2.0HDi C8 as per my previous posts. The EGR valve is now blanked off and the pipe disconnected. This seems to work fine, but hasn't done much to reduce the smoke or improve the MPG. I have found if I plug the end of the EGR vacuum pipe, it creates an audible hiss and a vaccum at idle from the butterfly valve (air doser). The air doser valve is closed at idle, but opens if you rev the engine. With the EGR vacuum pipe blocked, it also seems to stop the air doser from operating.

Is it better to plug the EGR valve vacuum pipe so the air doser operates, or leave the pipe unplugged. I can't tell any difference either way in terms of performance or economy.

[Hell Razor5543]

What is the state of the air and fuel filters? If they are not too clean, this could cause the problems you are having.

[bradspau]

Hi. Yes new air filter new fuel filter. EGR blanked off. Still black smoke, poor economy and MOT due soon

[Monkeyfeet]

You should definitely plug the end of the pipe that went to the egr valve to preserve the vacuum circuit. This hiss from the butterfly valve however is not normal, maybe a leak there? It would be good to rule out the simpler stuff (relatively speaking) before worrying about timing issues or any thing more serious though. Don't suppose you can relate the start of the smoking to any particular event at all engine wise? Could be something silly (I hope!)