Buzzing on TDCI engine stop

[rondeo]

An example of 2.0l tdci buzzing audible at engine switch off (11:35):

https://www.youtube.com/watch?v=lw2vyLqW_OA

I think this might be the turbo vacuum control valve leaking down, and indicates deterioration of the valve.

My LX did this at about the same km as Mr Badgertrix. Eventually the vacuum modulating solenoid valve failed resulting in no turbo and limp mode.

After replacing the valve the noise stopped occurring and the turbo worked again. No configuration is required and the valve is simple to install ($100+).

Now the zetec which used not to buzz has started buzzing, at about 150000km. I'll be replacing the same valve next week.

Seems to be a common fault judging by the internet.

[Mondaveo]

I hear two buzzes.
A short deep 'MRRZT' immediately on engine stop, and a long low droning for some seconds after all the other noises have ceased. Was surprised how long it carries on for when everything else has stopped.

I take it it's the second droning sound you're referring to? My car makes the first noise but not the second.

[rondeo]

I did have a suspicion there might be more than one possible source of the buzz, but as yet have no idea what the other might be.

The turbo modulating valve on my LX made more of a moo, quack or MRRZT (that last describes well the way it ends) until I replaced it after a P2263 and it fixed it. It made that noise for a year or two before failing.

The Zetec was making a longer buzz which went up in pitch at the end, so there might be a different cause for that. I replaced the valve late yesterday so I'll soon know and post result.

The valve has a foam air filter in a housing with a removable lid. Atmospheric pressure air is let in there to modulate the vacuum from the vacuum pump.
The amount of atmospheric pressure air allowed in is controlled by a solenoid operating a valve. The solenoid is controlled from the PCM by pulse width modulation. The turbo vanes are actuated by the resulting vacuum.

The valve is easy to replace except for the lower retaing nut which is almost inaccessible.

[rondeo]

Originally Posted by Mondaveo

I hear two buzzes.
A short deep 'MRRZT' immediately on engine stop, and a long low droning for some seconds after all the other noises have ceased. Was surprised how long it carries on for when everything else has stopped.

I take it it's the second droning sound you're referring to? My car makes the first noise but not the second.

I didn't notice the first noise on the video, just the long buzz.

I can confirm that after replacing the valve on the Zetec and stopping the engine six times while out and about, the buzz has gone.

Some info here about the valve (it's the brown one but with an air filter on the brown spigot):

http://www.pierburg-service.de/ximag...087_en_web.pdf

https://az25411.vo.msecnd.net/pdf/5/...17a_en_web.pdf

[rondeo]

This is the one I was looking for:

http://www.pierburg-service.de/ximag...076_en_web.pdf

Discusses the squawk. If it's normal I wonder why it only start doing it at 150000km.

[rondeo]

More fascinating trivia on the turbo valve (This valve is easily seen on R side of the TDCI engine):

http://onlinelibrary.wiley.com/doi/1....200790118/pdf

Production Hall (sic) capable of 32,000 EPWs (electro pneumatic valves) per day (really??). They are colour coded to type, happen to be brown in the Mondeo. The material is DuPont 'Zytel', a 35% glass fiber plastic.

And some bedtime reading:

http://www.freepatentsonline.com/y2010/0051842.html