I am new to diesels and this site, I apolgize if I am missing something obvious. I purchased a 1985 300SD (Cal. car) a few months ago. I ran OK at first (shifted hard) and occasionally it ran great, but it has been steadily losing power and putting out more smoke. The car now won't go over 2100 rpm whether in gear or not. I recently changed the fuel filters, cleaned the banjo bolt, replaced cracked/loose or gooey vacuum fittings, but nothing has worked. I have noticed that the bolt under the ALDA is loose and the ALDA itself will rotate about 45-90 degrees. I also noticed the trap oxidizer is leaking exhaust when the engine revs. It's frustrating becuase the car starts great and idles fine. I appreciate any advice.

Thanks!

forgot to mention. 1st thing I checked was that the throttle linkage on top of the valve cover made full motion to stop.

Are you sure the car still has the trap oxidizer installed? Or are you referring to the trap catalyst that MB installed in place of the trap ox under recall? Either way, an exhaust leak prior to the trap ox/cat could indicate a restriction. If the car does indeed still have a trap oxidizer, MB will replace it, along with your exhaust (and sometimes turbo) under recall. If you call MB and give them your VIN, they can confirm whether the trap ox has already been replaced by a trap cat.

The ALDA can be removed for purposes of testing whether it is functioning correctly or not. There are several threads that discuss how--search "ALDA removal" and the like. I am not an expert on how the ALDA works, but I know that people have messed with them and reported increased power but more smoke at WOT. I believe some people have removed the ALDA entirely; I think there are also those who feel this isn't a good idea. Someone who is a better mechanic than I will chime in soon, I'm sure.

I hope you get your issue fixed. My '85 is a California-spec model as well. MB says that the trap cat does not need to be changed (service life of trap ox was 30,000 mi, IIRC). My mechanic has mentioned that he has seen a trap cat get 'plugged up.' Mine was installed in 1995 (I think) and it still seems to be OK. The inside of both of these traps is filled with nasty/toxic/dangerous stuff, and there are threads about people trying to "hollow them out" and getting all kinds of nasty burns, etc., so please be careful and don't get hurt messing with it.

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Christopher
'06 Mercedes E350 station wagon
'85 Mercedes 300D (#2)
'84 Volvo 264GL Diesel
'79 Cadillac Sedan deVille

'85 Mercedes 300D (#1) sold back to orig. owner after 5 years on 8-1-06.

Either air intake or exhaust are probably restricted.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Thanks for the advice. I'm not sure if it is a trap oxidizer or catalyst. How do you tell the difference? I took the cover off the air filter and ran the engine. It didn't really change anything. I checked the front of the turbo and it is not clogged and spins. I'm not sure how to check for exhaust constriction.
I did make an observation yesterday. I don't know if it is related, but back when I first got the car and it would run OK (and sometimes better than OK) the ABS light would seem to arbitrarily alternate from being on constantly, to flashing, to being off. When the light was off, the brakes would be a little spongy and I could feel some vibration, but the brakes always worked. There didn't seem to be any pattern and the length of time it would alternate varied. When I had the AM radio on I could hear different interference sounds like servos and relays turning on and off when the ABS light was flashing. The PO had told me the ABS light had been acting up for about 10 years and he had it checked several times and they couldn't figure out why.
Now the ABS light is constantly on and I am struggling with the low power/rpm. (The brakes continue to work fine).

Thanks for any help.

If you still have a trap oxidizer (unlikely), you'll find it under the hood, typically right next to the exhaust manifold. It looks like an oversized white football. Unmistakable.

The catalyst is in the typical place under the vehicle and is also obvious by its larger size relative to the remaining exhaust piping. If you have the catalyst, you're going to need to disconnect the exhaust downpipe from the exhaust manifold and see if that cures your problem. Of course, its going to make a hell of a lot of noise when you do this, but noise is the least of your concerns.

If this test points to an exhaust restriction, you'll need to remove the downpipe with the catalyst and remove (or replace) the catalyst from the pipe prior to reinstall.

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Better to keep your mouth shut and be thought a fool than to open it and remove all doubt ----- Mark Twain

Is this a Trap Ox? You can see the soot on the left end where the diameter starts reducing.

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That's an interesting setup. Can you confirm that that device is between the exhaust manifold and the turbo? The exhaust gas passes through that device before reaching the turbo? I cannot quite tell from the photo.

One of the CA fellows probably knows straight off............

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Better to keep your mouth shut and be thought a fool than to open it and remove all doubt ----- Mark Twain

My thoughts exactly or at least close--What the hell is that??


Ok, I did a search and see that is the trap oxidizer. My confusion was/is caused by the fact that I have a distinct memory of seeing a picture of the 'white football trap oxidizer' that Brian described and it was above, not under the manifold. Did I invent that memory?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I've never seen a trap oxidiser but if I understand correctly it is between exhaust manifold and turbo. So the picture looks to fit that description.

If it is a trap oxidiser doesn't MB still replace them free of charge?

IIRC as they fail they kick out particals which ruin the turbo blades. I would think this would ultimately cause drastic loss of power.

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Diesel loving autocrossing grandpa Architect. 82 240d, 83 300TD with five speed, 03 Dodge 3/4 ton with cummins six speed; I have had about 33 benzes. I am building a 39 Studebaker Coupe Express pickup street rod at the moment in which I plan to install a 617 and a five speed manual.....or a 64 stude v8.

that is the trap ox; the recall on those is still active, call local dealer and give them the VIN to verify that it has not been changed (remote possibility that you have a replacement engine in which case you might be SOL as far as having the dealer do the recall). they will replace the trap ox and most of the exhaust system for free. this more than likely is the issue with your limited RPM (but also look at the ALDA issue since it should not be loose)

the system wouldn't let me upload these docs again so look here:
How Do I Work Safely with a Trap Oxidizer

post #21 has the recall letter and instructions in case the dealer is being dumb

absolutely, the dealer is supposed to check the turbo too for damage and if there is they will replace it as well

yes I think it does. The exhaust manifold is located under the intake manifold. That device is attached to the exhaust manifold on the left side and it is bolted to the underside of the turbocharger at the other end.

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Thanks for the info I will call the dealer on Monday.