I have found a couple threads about this issue, but all of them either do not really match my symptoms nor come to a helpful conclusion. This is about my 1985 300TD Turbo.

I have been having a loud distinct whistling at certain rpm. It doesn't coincide with the engine speed. It is most distinct at third and fourth gear. As it gets louder, it seems to take some power away and slows the car a little. Or, if I let off the gas a little, it will also become louder. It will get louder and the car becomes slower (maybe 5 mph slower, typically) until I push down on the accelerator and the whistle silences and it feels like the turbo really spools up and the rpm increases and off I go with a bit of power. If I stay cruising a ~65 mph, then it never happens. But, at around 45-50 mph, it gets very annoying.

The previous owner told me it was a vacuum leak, other similar threads seemed to propose it was an intake/exhaust leak. Something else I just read talked about bypassing the EGR, maybe there could be a leak there?

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"Blessed are the cracked, for they shall let in the light." - Groucho Marx

The EGR could be stuck or plugged. From what I've researched there doesn't appear to be any downside to removing the EGR unless some government agency will be looking at your emissions. That might be a good next step.

Dkr.

I had this issue once already, sounded like a screaming cat under the car. For me it was an exhaust leak robbing the energy that would have gone to the turbo. Mix liquid dishsoap with water in a spray bottle and spray everything with the engine off.. and then turn it on and let it idle & look for bubbles. Sometimes the leak is so significant that it will just clear the area so keep spraying. I would do this first before messing with the EGR just because it's so simple.

Historically.... a whistle is caused by a suction leak....

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

I usually find leaks in the boot between the air cleaner housing and turbo inlet on these applications when they are making noise like that.

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Jim

Had a td turbo that shrieked! What it was, was, the small hose to the wastegate broke off & the sound bounced off a high wall and was really LOUD, besides loss of power.
-c-

OP - I had nearly identical experience with an SDL I picked up March'13. My input in red:

Here's the skinny. It is a leak and is also dependent on engine rpm. That loud whistling is coming from the ARV valve on the turbo as result of a weakened spring that opens now merely from boost pressure.

- Verify you have the ARV wart on the compressor housing (if not, we done!)
- Remove ARV cover (4xscrews) carefully as to not destroy diaphram/gasket.
- Pack enough "xyz" material between top of valve and inside of affixed housing (I epoxied a stack of washers, the idea is to not let the valve open at all.)
- Attach cover
- Enjoy whistle-free motoring. YAYYY!

This can also be accomplished by simply epoxying/JB-welding the port itself shut. There are threads detailing how. I wasn't planning on having the turbo off the engine so I didn't go this route myself.

MBZ123

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1987 300SDL "Rhona" 218k
1986 300SDL "Johanna" 166k - Abducted 5/15 outta SFV Reward 4 info
1984 300TD "Petra" 212k - Parts yard pirate, arrrrgh
1982 300CD "FrankenFemme" 178k - Eyes only TS-XWRKS transplant abomination (loc. classified)
1980 230CE "Lulu" aka "Terminal" 277k - Dying the slow death
1985 300CD "Gerda" 203k - She ain't playin' SOLD
1983 300TD "Svetlana" 240k...and pleading for more. SOLD


"What a heavy load Einstein must've had...F&@%!NG morons everywhere!" - David Lynch

Mebz, thanks for that! Gave me some confidence in my original suspicions. This definitely sounds right on, the ARV is just dumping my boost pressure at improper rpms due to a worn out spring.

Considering doing an EGR delete... This thread shows deleting/bypassing some of the wiring associated (first time I've seen anything about doing anything more than just replacing it with a plate/cover). But first I'll try and get that ARV closed off. Doing some more homework on the EGR in the meantime.

On the bottom of that u-shaped plastic duct that goes from filter housing to turbo is caked and wet with oil on it's underside near it's ends. I've read that this is normal for high-milage engines, can someone tell me why this happens? Is it coming in from the dirty EGR air?

This little blog post seems to be a decent brief rundown of the EGR, ARV and ALDA and why people get try and rid of them.

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"Blessed are the cracked, for they shall let in the light." - Groucho Marx

Okay but just a word of caution to moderate your enthusiasm for removing the ALDA. Do some more reading on that before you consider it.

If you plan to use your car normally (that is, you are not looking to be a diesel hot rodder), and your ALDA is functional, there is no reason to remove it.

If OTOH you get wood watching those chipped diesel trucks blow coal smoke, then have at it... but make sure you understand what you are doing beforehand.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

Oh no, definitely not touching the ALDA, not if it's working properly. The ALDA seems to get grouped with the EGR and AVR as anti-productive systems. I'll most likely disable the AVR then if no other problems arise the EGR will stay until I have reason or inclination to do otherwise.

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"Blessed are the cracked, for they shall let in the light." - Groucho Marx