Chat Clunk when turning engine off 2004 TDI 90

[audifan]

@Howey

Yes and no. Unplugging the vac pipe will disable the ASV so that the air flow is never shut off. BUT if the pipe or valve is already leaking vacuum you will not prove anything.

On the AMF the ASV ONLY works to cleanly close off the air passage by the vacuum operated linkage when the engine is turned off. It immediately reopens the valve to full bore by spring action.

 

[Howey]

@Howey

Yes and no. Unplugging the vac pipe will disable the ASV so that the air flow is never shut off. BUT if the pipe or valve is already leaking vacuum you will not prove anything.

On the AMF the ASV ONLY works to cleanly close off the air passage by the vacuum operated linkage when the engine is turned off. It immediately reopens the valve to full bore by spring action.

So it's more likely the vac pipe is compromised and the asv isn't actually active at all, is that logic correct (first time for everything lol)

 

[audifan]

The ASV is spring loaded fully open and that is the position it operates all the time until you turn the key off. At that point it is vacuum operated to close the air passage inside the valve. As the vacuum dissipates the valve reopens under the spring pressure ready for the engines next start.

If the ASV is not functioning in an AMF then there is either a mechanical linkage issue, or the required vacuum is not available when the engine is shut down .

Diesels operate at full bore air all the time, unlike petrols that no pun intended "throttle" the air flow entering the engine. Diesels operate by increasing the fuel flow and that is why the PD pump engines are so good compared to single diesel pump engines.

To shut down the diesel cleanly the injectors are disabled and the ASV closes its butterfly valve to stop the air flow. The ASV is also a safety device to prevent run away situations where the engine is burning its oil as fuel to the point of destruction as seen in many youtube videos. In this case injectors being turned off make no difference as the engine has found another source of fuel - its engine oil.

 

[Howey]

If the ASV is not functioning in an AMF then there is either a mechanical linkage issue, or the required vacuum is not available when the engine is shut down .

Diesels operate at full bore air all the time, unlike petrols that no pun intended "throttle" the air flow entering the engine. Diesels operate by increasing the fuel flow and that is why the PD pump engines are so good compared to single diesel pump engines.

To shut down the diesel cleanly the injectors are disabled and the ASV closes its butterfly valve to stop the air flow. The ASV is also a safety device to prevent run away situations where the engine is burning its oil as fuel to the point of destruction as seen in many youtube videos. In this case injectors being turned off make no difference as the engine has found another source of fuel - its engine oil.

Sweet! Many thanks for the info will take a butchers at the silver one when I get a chance, no major problem thou.