I recently purchased a 1985 300D and noticed the EGR valve has been disconnected...the hoses that were connected to it have been blocked off.

Why is this?

to preserve your motor. get better mileage, and power, and keep the intake clean.

... I mean for testing of the vehicle, it should be put back into full legal compliance first chance you have...

How so? Because it keeps particulates out of the intake? I'm new to all this and very curious. I've read a couple sites that say the recirculated exhaust actually cools the combustion process.

Thanks.

Soot in the exhaust will adhere to all oily surfaces, and make a cakey goo that will plug up the intake, the head, the valves, the motor itself. not to mention the fact that it dilutes the intake charge (which is what it is designed to do...) with partially burned exhaust...

I purchased and just received Brian's EGR removal kit for my 84 300SD. The car now has 171K on it...will removing the EGR at this point really make that much of a difference? The engine seems to be quite healthy, by the way.

I haven't looked at the instructions that Brian included yet, but I assume it's a fairly simple fix.

Also, vstech, I believe I've read a previous post where you've stated that it's very important to reconnect a disconnected/bypassed Overboost Protection Valve (that connects to the ALDA). Is that true? If so, it's okay to disable the EGR but the OPV needs to be in place and functional? I removed mine, which was already bypassed when I purchased the car last year, and blew the carbon out of it, however I'm thinking of just buying a new one to replace it and then trying to figure out how to re-plumb the vacuum lines to hook it up again (if it's really necessary).

Thanks in advance.

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1986 300SDL - 116K
2014 Prius Plug-in (company car)
2014 Q5 TDI (wife's car)

The sooner you remove/bypass the egr, the healthier your engine will stay. Yes, you are sending particulate matter through the intake, then engine. You're damaging it, albeit just a little, whenever exhaust gasses are re-burned.
My CD has the switchover (overboost) valve bypassed, I bought it that way. No issues. The turbo has a wastegate that performs the same function. An MB mechanic stated when overviewing my car, remember his goal in life is to perform work so the dealer gets paid, to not worry about it. But if I wanted the car bone stock, they'll replace it and he'll work up a price for me.
It has nothing to do with the egr system. Your plugging off vacuum lines when you bypass the egr system, not pressure lines that tell the ALDA how much fuel to allow.

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83 SD

84 CD

That does apply to gasoline engines more so than ours. What you read is correct, it is to slow the combustion process and stop spark knock. Since diesels ignite under compression, by design, optimal spark timing and reducing knock are not truly 'part of the equation.' Stopping the soot is the key to long engine life.

Once you've stopped the soot, think of it this way...
Octane (either the molecule or the fuel's octane rating) is to REDUCE ignition under compression. Cetane (also, both a molecule and a rating) is to PROMOTE ignition under compression.

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1987 300D (230,000 mi on a #14 head-watching the temp gauge and keeping the ghost in the machine)
Raleigh NC - Home of deep fried sushi!

it all depends on the problems and issues you have with your car.
under normal circumstances the OBP valve does nothing. it's open. and it's true, the wastegate will protect as well, but I like having both enabled, wastegates can stick, and if it did, I'd rather not overfuel the motor and blow it.

Too much fuel getting to the engine will result in black smoke. If you have a stock set up, you have no worries.

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83 SD

84 CD

I do see black smoke coming from my exhaust, but mostly only when it's cold or when I take off from a start (particularly when I floor it, such as getting on the freeway). But most old 617s that I see driving around have some form of minimal smoke coming out of their exhaust pipes.

I guess I won't worry about the Overboost Protection Valve right now. How do you tell when your wastegate isn't working correctly?

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1986 300SDL - 116K
2014 Prius Plug-in (company car)
2014 Q5 TDI (wife's car)

Some black smoke is not a problem.
Check here http://www.google.com/search?client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&channel=s&hl=en&source=hp&q=turbo+wastegate+failure&btnG=Google+Search
Or you could mount a pressure gauge in the cabin. Full load between 0.7-0.8 bar. http://www.asknumbers.com/bars-to-psi.aspx I understood 14 psi was okay, but maybe not, I get 11.6 maximum.
I wonder how many stock turbos have failed, in any fashion. I would think some, somewhere.

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83 SD

84 CD

Thanks for the links! The guy I bought the car from told me that he had to replace the turbo not too long before I bought it. He said he was driving along and the turbo started making some really strange noise (not sure how he knew it was the turbo). Anyway, he shut it down immediately and had it towed for service.

One thing I notice about my turbo is that I really can't hear it, except when I release the accelerator, I can hear the turbo spool down (the high pitched whistling noise). I actually like the sound of a turbo and was a bit disappointed that it wasn't more noticable. I've driven other turbos where it is (Audi 2.7T V6, Ford Powerstroke, GM Duramax and of course the Detroit 6V92T).

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1986 300SDL - 116K
2014 Prius Plug-in (company car)
2014 Q5 TDI (wife's car)

It won't hurt to have the over boost valve hooked up, but it's another redundant set up.
If the turbo was indeed making noise, sounds like a failed bearing. Anything mechanical can fail, I know, it just seems a failed turbo is quite rare.
Of the four turbo MB's I had, they all sound a bit different.

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83 SD

84 CD