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  #1  
Old 12-13-2005, 04:02 PM
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Turbo noise, what's this vacuum valve??

I have a 1984 300TD (wagon). For the past couple of months, the car has made a strange intermittent whistling noise. It happens primarily after the engine is revved/accelerated....when pressure is let off the accelerator, and as the engine winds down, a "weeeeeeee" noise is heard as the engine decelerates past a certain rpm range. There are times when I can sustain a specific vehicle speed/engine rpm and sustain the whistle noise, but it is most pronounced when the engine is winding down from high rpms.

I found the source of the noise, but I dont know what the item is.....there are two vacuum lines, located in the same vinyl sleeve, that are routed up in front of the turbo...one of them attaches to the egr valve, the other attaches to some type of valve...a round metal valve with a triangular base mounted with three bolts onto the exhaust gas cowl of the turbo next to where it connects to the exhaust manifold...when I remove the vacuum line from this valve, the noise no longer happens. What is this vacuum-controlled valve on the turbo. Note that this car has a regular federal air cleaner mounted on top of the turbo, and no trap oxidizer, but I believe there are some California-related emissions components on this car...possibly specific to 84's and 85's (I have a turbo from an 85 with the same valve). Anyone know what it is, and what it does? Can I just put a ball bearing in the vacuum connection to this valve and run the car without any problem? I am hoping to get one of the EGR kits from B.C. and I hope that this valve is one of the items that can be bypassed. I haven't tested boost pressure on the car, and don't know if it may be related...this 84 wagon does seem to lack the "peppiness" of my previous 85 sedan.

Any suggestions regarding the squeal and the turbo-mounted vacuum valve?

Thanks very much,

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)
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  #2  
Old 12-13-2005, 04:15 PM
TheDon's Avatar
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well your wagon may lack peppiness because its .. well its a wagon.... when ever i accelerate i can hear turbo whine and when i let off and it winds down it sounds like when a big rig shifts.. loud high pitched whine that evens out... well now that loud but i listen for the turbo because its cool..also have you cleaned the banjo bolts or adjusted the alda at all maybe your bajno bolts are clogged with crap
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  #3  
Old 12-13-2005, 04:30 PM
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Location: Norwich, VT USA
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Hi MArk,

if its the blue line like in the picture (from an '85 engine bay - not mine) I think its refferred to the circulating air safety valve" on the vac. diagrams....Beyond that I can offer little help off the toip of my head....for what its worht at idle after a run my turbo on my VW whistlers a nice high pitch whine that semms to ssay "all is good".....

Cheers!
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Turbo noise, what's this vacuum valve??-85-cropped.jpg  
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  #4  
Old 12-13-2005, 05:05 PM
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Thats it!

Hi Rob...thanks for the thumbnail photo...that's it exactly ...the valve with the blue line. When I detach that vacuum line, I no longer get the noise. The whine noise does not seem like a normal turbo noise....at first, I thought it was a failing bearing in the alternator.

I have cleaned the banjo bolt etc., but I have not adjusted the ALDA. The car actually does run quite well. But having formerly driven an 85 sedan, I find the wagon in comparison more "sluggish" and poorer handling (due to suspension differences, weight of car, etc.).

I will have to do a little research on the "circulating air safety valve" ...sounds like an emissions control component that may be destined for the "ball-bearing-in-the-connector" treatment.

Thanks,

Mark

P.S. Rob, I moved the junk car further up in the driveway to make room for other cars...looks like it will be here for the winter!!
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  #5  
Old 12-13-2005, 05:13 PM
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That valve is the ARV or Air Recirculation Valve. It allows air, post compressor air, to be released back into the turbo inlet. Effectively this is dumping boost pressure by allowing it to escape back into the inlet air stream. Why this was done is a mystery. I am guessing that it has something to do with the EGR/emissions system. I have the same setup on my 84 300D. When I first got the car I noticed that if I was at cruising speed and I accelerated there was a noticeable lag in turbo response. I disabled the ARV by removing the vacuum line and then I unbolted the 3 bolts from the housing, removed the cover, careful its spring loaded, and dropped a SAE 5/16 nut in the cover/spring seat. This increases the seat pressure of the valve so there is no way it will open under boost pressure or any other way. Getting the cover back on with the nut in the spring pocket is a little tougher with the sizeable increase in spring pressure but it can be done. This disabling of the ARV caused the turbo response during cruise conditions vastly improved. Now the turbo works as MB intended not some nitwit on the CARB board. RT
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  #6  
Old 12-13-2005, 09:44 PM
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Great!

Thanks very much for the useful info. I was hoping that this thing was a useless piece of crap that I could disable. I am looking forward to doing a complete EGR lobotomy on the car, and then adjusting ADLA, boost pressure, linkage & transmission adjustments, etc.

Thanks again,

Mark
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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)
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  #7  
Old 12-13-2005, 10:17 PM
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You may be hearing the turbo spooling down due to a monentary reduction in exhaust pressure, but the rotor still spinning at high speed.
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  #8  
Old 12-14-2005, 08:36 AM
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To clarify......Would removing this valve from operation compromise over boost protection? ie its not related to the switchover valve or something? Please pardon my ignorance....

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1980 240D Euro delivery 4 speed manual silver/blue
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