I want to thank all of you who chime in here. I probably know more about my diesel than most of these "Kmart" mechanics out here. Again thanks for all your input and wisdom (even though it might sometimes come from mistakes we make)!!! I was doing a search for a miracle. Low and behold, I got to reading this thread. It so happens I have a 1985 300SD with over 200K on the odometer. I always thought the same things the mechanics say....Its a diesel...it has to be slow. But it got to a point where I also felt the low acceleration was a driving hazard and I was asking for a major accident if I did not look into what was going on. So, after reading some threads here, I did as some of you suggested...I bypassed the switchover valve and WOW!!!! my car is back to life. I started laughin when she took off becasue it was like a rocket. As I inspected further, I noticed the line coming from the manifold to the switchover valve is pretty cruddy, so cleaned the banjo bolt, cleaned the line, cleaned the switchover valve and the banjo bolt at the ALDA (I finally know what it is and what is does YIPEE) all with brake parts cleaner. When I put everything back together and reconnected the lines to the switchover valve...low and behold I was back to turttle land. I puched the accelerator....NOTHING! So I got out and bypassed the switchover valve again....and Yup, she was a rocket once again. My question, however, is...I only have when I was taking the switchover valve out to clean it, I noticed that there are only two lines coming from it..one over the top of the switch from the banjo at the manifold, and the one, also from the top, but protruding out going to the ALDA. There is also another orifice one on the bottom of the switch, but nothing attached to it. I scanned to see if there was a hanging vaccum line somewhere, but found nothing. Is this supposed to be this way, or is there something needing o be attached to it. Also, is this why my car losses power when connected to the switchover valve? Please help!!!

1) Yes, your SOV has three ports, but will only use two of them. The third normally has a little plastic cap to keep dirt out, but that's not important.

2) You are losing power because the SOV is plugged. If you can't clean it with compressed air and carb cleaner, just replace it. (There's a very slim chance it could be triggered electrically, try disconnecting the electrical connector - if you still have no power, then yes it's clogged with soot internally.)

3) If you have not yet adjusted the ALDA, you may experience another "YIPPEE!" if/when you do this.

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

GSXR THanks for chimin in here. Thanks also for your advise. I have a troubling question. You know when you get these gut feelings?? Well I'm having one right now. Somehow I feel that these vaccum hoses connected to the SOV are connected incorrectly. How should they be connected. The other thing is that I am really hesitant in tinkering with the ALDA, after reading so many threads of people saying DONT TOUCH!!! and then others say TOUCH TOUCH but VERY SLOWLY CCW. What do you think I should do??

1) I forget the exact connection. You should be able to blow air through the two SOV ports when not energized, and you should not be able to blow through when energized with 12 volts. I vaguely recall the manifold (pressure source) going to the bottom port, and the ALDA connecting to the center, with the open/capped port on top. (?)

2) About the ALDA. Just be gentle with the adjustment. Loosen the setscrew, rotate the shaft gently 0.5-1.0 turns CCW, gently snug the 10mm nut down again. Tweak as necessary (you want as lean as possible, CW, without a noticeable power loss.) Worst case if the aneroid capsule breaks (very rare unless you force the setscrew past the limit), you have to find a used ALDA from a junk yard - probably $25-$50 for a new one, or less from a Pick-n-Pull. Most cars seem to need 1.0-1.5 turns.

Thanks GSXR,
I'll tackle that this weekend when everything is quiet around campus and no body to bother me, that way I wont make a mistake and ruin something. I'll keep ya posted!!!

ayalar007, i've been following up on your posts but just reading along quietly. I have done what you have done so far. The way you describe, it does sound like your switchover valve is hooked up incorrectly. I'll take a picture of the one from my 300SD later.

I have cleaned the boost lines (the 300SD was fairly clean, the w123 300D was crudded, W124 300D was fairly clean too), cleaned the banjo bolts (didn't perform on the 300SD, W123 300D crudded horribly, W124 300D also pretty bad), did the switchover valve on the W124 300D, but tuned the alda 1.5 turns CCW on the W123 300D and 1 turn CCW on the SD. Wow - 300SD, WOW! on the W123 300D, and WAHAHAHAHAHA!!! in the W124 300D. All of them can hike up a hill faster than before but especially so in the 300SD and W123 300D (put it this way, it can now go up a hill FASTER than flat level acceleration before).

Don't have the guts to do a valve adjustment or turbo waste gate adjustment yet. Going to do a diesel purge on all 3 when the opportunity permits.


I, too, would like to thank everyone on posting these tweaks for the OM617 motor and Dave in particular for the OM603. Without you guys, my W124 will be easily caught up to by properly tuned OM617s and my 617s will be "they're like that because they are diesel and have alot of turbo lag" - Mechanic John Doe


Perhaps we should have a sticky for the first things you should do after acquiring a diesel benz and its "sluggish"??? Does that sound like a good idea?

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Jason

00 Subaru Legacy (fun wagon)
96 Nissan Sentra (disavowed)
82 300SD (garage queen, will run again hopefully)
87 300DT (Gone: 10/15/2010)

Jason,

Glad to know that what I have posted has helped someone else out there. I guess that what this forum is really all about. I was around your ne4ck of the woods two weeks ago. Had I known you were experimenting with these things I would have looked ya up, would have loved to seen your "babies".

As for the picture....I would Really Really appreciate it. I really do thing that the two vaccumm lines coming from the top are incorrect. But I'll wait for your pictures before I do anything. I'm curious....did you test drive the 300SD after you cleaned the banjo bolts and the SOV. If so, did adjusting the ALDA make a better improvement afterwards??? Noticable???

Yes as a matter of fact i did. The 300SD wasn't as slow as the W123 300D even before the adjustment, just a tad sluggish before the turbo kicked in. After 1 turn CCW, its as fast going up a slight incline as it was before on a level surface.

The pictures i took last night weren't too good (it was already dark and the images didn't come out right). I'm currently in class right now so i'll snap the pictures when i get home.

About your switchover valve, on my 300SD (1982), its a little brass colored cylinder with all 3 connctions on the bottom. I think that your car has the same SOV as the W123 300D.

__________________
Jason

00 Subaru Legacy (fun wagon)
96 Nissan Sentra (disavowed)
82 300SD (garage queen, will run again hopefully)
87 300DT (Gone: 10/15/2010)

The crossover valve does nothing other than relieve the pressure coming through the line to the ALDA. There is pressure switch somewhere that will energize the switch. When energized it opens and the pressure in that line blows out into the atmosphere. I have been told this is a safety measure to protect the ALDA, and to reduce the emissions that could come from too much fuel being squirted through the injectors.
When you take one off, put it in your vise and hook up a couple of lines there. You should be able to blow through it. If not, then it is plugged. If it will not clean up. replace it. Hook up 12 v to the two leads. Then you should be able to blow through the intake side and the air will come out the vent. That is all it does. A simple bypass will work of course, but that may cause your car to pollute, and you do incur a small risk to the ALDA itself.

that's pretty close. When properly set up, the ALDA connects to the atmosphere vent when energized, and the boost/pressure port is simply blocked. The switch that triggers this is a hexagon-shaped widget in the intake manifold. It is rated to trigger at, IIRC, 1.15 bar +/- 0.10 bar. (Or, 15.0-18.5 psi). My switch was bad too - I tested it with a MityVac, it didn't trigger at 20psi. I cleaned it up and banged on it and now it triggers around 18psi.

BTW - it's an engine overload safety, to protect the engine from meltdown if the turbo wastegate were to jam open or otherwise allow boost beyond the normal specified range (0.75-0.85 bar for 617's, 0.85-0.95 for most 602/603's). It save the engine by eliminating the fuel enrichment - that's what the ALDA normally does, allow more fuel as boost pressure rises. As the engines get older this circuit is much less necessary, since the IP's lean out over time and the probability of excess fuel under overboost conditions is almost nil (IMO).

You say this would serve to protect the engine from meltdown during a turbogate jam? Sounds good to me. I had been told it would protect the ALDA itself by a very good MB tech. But then, he doesn't have all the truth either.
I have often wondered if the mechanism there gets out of sorts with age also. Seems that when these old diesels are throttled hard there often is a lot of black smoke. I know the ALDA should be adjusted, but is there anything on the this that needs attention besides the cleaning?

The ALDA doesn't need protection - take a peek at the insides and see for yourself:

http://www.meimann.com/images/mercedes/OM603_injection/


A lot of mechanics, unfortunately, do not fully understand how the diesel injection system really works. For a lengthy - but accurate - explanation, check out this PDF file from the factory service manual:

http://www.meimann.com/docs/mercedes/fuel_system_desc.pdf


The reason diesels blow black smoke is usually (but not always) due to excess carbon buildup from extended idling, and periods of low engine load (i.e., cruising at 55mph on flat roads). Diesels don't like light loads. They want to be run hard and at high RPM's. Do a few full throttle 0-60 runs (or higher, if possible) and the smoke should get less and less, until it's pretty much gone. On a car that has been driven sedately for months or years, it could take weeks to fully 'blow the carbon out'. And as the carbon blows out, you may see truly impressive black clouds out the tailpipe. Drive the car like you stole it - aka 'Italian Tuneup'. After a while you'll get a lot less smoke! I recommend at least one or two full-throttle runs to the redline with each tank of fuel. Freeway onramps work great, as do long/steep hills, or deserted back roads. Hopefully you have one of those available near you.

Now if the car smokes constantly, or continues smoking after the Italian Tuneup, etc... there may actually be a problem. Usually a dirty air filter, or perhaps a mis-adjusted ALDA. As the IP gets older, they lean out. The reason is, the ALDA presses down on a spring in the IP. Boost pressure collapses the capsules inside the ALDA and let the spring press upward, adding fuel. As years go by, my theory is that spring gets weaker, and can't push up as hard as it used to against the ALDA's pressure - resulting in low fuel delivery. Adjusting the ALDA base setting helps a lot (the usual 1.0-1.5 turns CCW) but the proper calibration would require adjustment on a Bosch injection pump machine, which usually isn't necessary (but nice if you can afford it.)

The only other thing that needs 'attention', IMO, is to verify that the ALDA is not leaking. You'll need a MityVac that make pressure to test this. Connect it to the ALDA and pump it up. It should pump up to 10-15psi and hold that pressure, or at least leak down slowly. If it leaks as fast as you can pump the MityVac by hand, meaning you can't get it over ~5psi, the shaft seal has failed. A new seal is $5-$10 and takes maybe an hour at most to replace, working slowly. This doesn't really rob much full-throttle power, but it DOES steal part throttle power! I had this on my car and a new seal fixed it. Details are here:

http://engine.articles.mbz.org/diesel/alda/

Well...here's where I am at presently. If you ask my firends, they'll all tell you that when I am passionate or excited about something, I get "ants in my pants." Well its been no less true here. I was really excited about tweaking the ALDA, now that I have read so much about it thanks to all of you on this forum. Anyway, I go to the car and noticed a black cap on the ALDA. I figured I had to pop it off to get to the screw which I attempted to due. Well all I accomplished was to break the little tin around the plastic cap also. Was that supposed to happen??? I included some pictures so you can see...and also one of my little girl!

You'll also note how I put the hoses coming to and from the SOV. The top hose is coming from the manifold while the bottom hose is going to the ALDA.

Let me Know!!

Attached Thumbnails

       

1) I think your hoses are backwards, but it won't matter really, it will work the same (just vent boost to atmosphere if it triggers).

2) You can either leave the tin can in place and carefully use a small socket to adjust the ALDA, or preferably just rip it off entirely as shown below:

GSXR:
I noticed that your screw doesnt stick out as much as mine looks to be. Is it that my screw had been turned CCW too far at one point. I haven't touched it yet and the cap was still in place when I actually took it off. What do you think??

Also, thanks for the tip on the hoses, I'll invert them tomorrow!!