Recently I bought a great condition 91 300D 2.5 Turbo and am just slowly going through things and checking everything out. What I found today, is that there is a vacuum actuated valve downstream of the turbo (basically in between the turbo and the intake, almost right on top of the engine) that is not connected to the vacuum system. The hose is just wrapped up and where it used to be connected to the vacuum system just has a bolt sealing the hole.

I imagine this might be some kind of anti-shudder valve or something like that, but am not sure. Does anyone know what it is? Also, I have no idea why it was disconnected, but it doesn't seem to cause any problems and there really is no shuddering when I shut the engine off... is it not important and so can be disconnected like this?

Any ideas? TIA

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1991 MB 300D 2.5 Turbo (207000km) (now gone)
1993 Audi 100 CS Quattro (300000km)
1999 VW Jetta TDI (290000km)
2002 Audi A6 3.0 Quattro (150000km)
2005 MB E320 CDI (34000km)

I could be wrong, but this sounds like the previous owner disconnected the EGR emissions module. If this is the case, I would, as I'm sure most on this diesel forum would, leave it disconnected!

If it is not the EGR, somebody here should point this out. I'm guessing it is the EGR because I am not aware of anything else it could be except for maybe the waste gate actuator which is vacuum powered on my 87 300D and likely yours too. If it is the waste gate disconnected, you should have that reconnected as it prevents over-boost.

One exception, if your state emissions program requires you have this EGR installed you will have to deside if you want it on-line, or off!

The EGR as I understand it will glog up a lot of things and add poor performence as well.

Slop from the EGR is minimal if you use synthetic oil since the oil won't coke in the intake. Thin film after 50,000 miles, just wipes off.

The EGR needs to be working on the 91, or the boost won't come one (boost is electoncially controlled.

The valve, if between exhaust and intake, is almost certainly the EGR valve. Hook it back up and see what happens -- if you get terrible peformance and lots of black smoke (like a squid, for instance), the EGR valve is sticking open and needs to be replaced.

You might get a surprise at how much more power you have, too!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thank you Peter. Peter is right, I wasn't fully sure as I know the later 300D's had electronics.

I wasn't aware the EGR needs to be connected on these later engines to perform boost. So I wonder what it is he has disconnected and if his turbo is putting out?

Thanks for the info.. I know the previous owner was having trouble with intermittent black smoke problems while driving. A reset of the car fixed the problem each time.. (so perhaps that would let the valve close and then re-open). Does that make sense? I suspect that's why it was disconnected, because they found that stopped the problem.

I also have a Jetta TDI and have taken the EGR valve out before and cleaned it... can these ones be cleaned, or do I just need a new one?

Are you sure that the turbo won't work if it's disconnected? Turbo _seems_ to work.. I mean if I floor the pedal from 0-100km/h is about 13-14 seconds, and from what I've read that suggests the turbo is working.

TIA for any more ideas!

__________________
1991 MB 300D 2.5 Turbo (207000km) (now gone)
1993 Audi 100 CS Quattro (300000km)
1999 VW Jetta TDI (290000km)
2002 Audi A6 3.0 Quattro (150000km)
2005 MB E320 CDI (34000km)

13 or 14 seconds may be right, but I am not as well versed on your engine as I am on my six cylinder OM603 which runs 11 to 12 seconds.

I'd be curios as to what and why the disconnect too!

Steve........

87 300d should be in the range of 9.5-10 with the trap oxidizer replaced.

If you feel considerably more power above 2000 rpm, the turbo is working. 13-14 sec is OK, but not great.

You should be able to pull trouble codes, I think (may require proprietary equipement!), but intermittant black smoke and poor performance is certainly a bad EGR.

Cleaning usually won't fix a binding actuator, though, best to replace. If you get proper boost control without it, you can leave it alone.

I plated off the EGR on the Volvo -- new valve was $450!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

A picture would make this very easy.

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I don't have a digital camera at the moment..

As far as turning up the ALDA, will turning it up decrease fuel economy? I like the economy I am getting right now and don't want to make it burn more fuel.

__________________
1991 MB 300D 2.5 Turbo (207000km) (now gone)
1993 Audi 100 CS Quattro (300000km)
1999 VW Jetta TDI (290000km)
2002 Audi A6 3.0 Quattro (150000km)
2005 MB E320 CDI (34000km)

No. A properly adjusted ALDA will not hurt fuel economy. If you lose MPG, you went too rich. To adjust, turn the setscrew CCW (richer), or add thicker shims, until you can't feel any more power gain off idle. Then turn in back (leaner) just a bit, but not enough to feel a power loss. This is about the optimum setting. You may see a puff of black smoke leaving a stop (not a cloud, not a stream, just a puff). There should be no extra smoke at WOT or anything else. A 1.25mm thick washer equals roughly 2 turns on the setscrew, so you'll probably need to file down washers if you want to use that method. Typically, 0.5-1.5 turns CCW is needed.

I am going to have a week or so in December to fiddle around and clean everything up, and then hopefully adjust the ALDA too if cleaning and checking the hoses (including the one going to the ALDA) doesn't fix the problem.

So, that's good news.. but now I want to know for sure what this valve is. I've attached two pictures of it, one close up and one with arrows pointing to some things on it.. sorry it took so long to get the photos, but I haven't been around much lately and just haven't had a chance.

If anyone has a picture of what this valve looks like inside, that would be awesome!

Now, back to the question... what exactly is this valve, now that there's a picture to look at?

__________________
1991 MB 300D 2.5 Turbo (207000km) (now gone)
1993 Audi 100 CS Quattro (300000km)
1999 VW Jetta TDI (290000km)
2002 Audi A6 3.0 Quattro (150000km)
2005 MB E320 CDI (34000km)

Looks like some kind of restrictor. The Cummins ISX uses something like that to create a pressure drop to suck exhaust gas from the exhaust manifold to the intake under boost without a pump.

Edit: You can see the restriction tube just after the main opening at the top. It is basicly just a venturi (like a carb uses to draw fuel out of the bowl).

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