Done.

Yes, you can bypass the overboost protection system. But, it's not a good idea over the long term. If you lose the wastegate hose, the system has no control over an overboost condition. Far better to replace the solenoid or thoroughly clean it out.

Yes, getting the boost up to 12 lb. would help your performance. You'll need a detailed procedure for adjusting the wastegate...........I believe I have it at home..........or another member will provide it.

Yes, adjusting the ALDA is always desirable on these vehicles. Make sure you are very careful in turning the adjustment screw and do not force it. If you break the screw, you're toast. You should adjust the screw in 1/2 turn increments.........counter-clockwise........until the vehicle starts to smoke when you mash the pedal from a standing start.

You'll need a source of pressure to test the switch. Some Mityvac's have this capability. When the pressure exceeds 15 psi, the switch should ground to the manifold.

To test the solenoid simply requires that you ground the wire to the pressure switch. The solenoid should close and the horizontal leg that goes to the ALDA should now be vented to atmosphere (via the cap on the top of the valve).

Thanks Brian.
I will test the sensor, as my mityvac will push as well as pull.
The valve is my current guess. I have a couple tests planned for it.
I'm thinking that it had a piece of debris blown into it, that has not come out with repeated cleaning.
And I guess I will start researching the procedure for adjusting the wastegate.
The ALDA seems pretty straight forward, just have to be careful.
I have no intention of running this car without a functioning overboost system. It's doesn't have to be my daily driver, I just prefer it to be.

Might be a week or so until I get some results, but I will post what happens next. Let's hope for nice weather in NE.

Brian, I just got VDO boost gauge and @3500RPM in 3rd I only get 8PSI. 9-9.5 is the most I get. Interesting that I get 5-6 PSI reving in neutral to about 4000RPM. Then, upon acceleratin it goes up very fast but only to 9PSI. Is that normal?
Car is strong and goes to 60 in 13s but the boost numbers are low, right?

That's typical on the older 617's. You can get a bit more performance if you adjust the wastegate up to 12 psi. The 0-60 times will drop into the 12's.

http://www.serenitysys.com/MB/Service_Info/Turbo_Tweak/tweaking_the_mercedes_617_turbo_.htm

Thank You! will try that and do 3 turns. that should bring me up to ~12PSI

No way. Slightly better aerodynamics help the W126 a little bit, but nowhere near enough to shave a full 3 seconds off the W123 0-60 time without additional fuel from internal pump adjustments.

Even 13 seconds is abnormally fast. Are you measuring 0-60 times in both directions and averaging the two times? A slight downhill slope can make a big discrepancy.

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Hi Forced

I was a little surprised too but I double checked to be sure, two more runs on a flat road, well it's not 13 exactly but still under 14s. I would say 13.7 but the time needle shows 57 (in my case 60MPH)

I wonder what this chart says but it seems slow what they show there 17-18 sec. 14-15 is very common and check this guy, he gets under 12 with nasty grease and no fancy mods like MYNA

http://www.youtube.com/watch?v=eFZolVNszqI

Stock IP.

Time measured via G-tech pro in both directions............multiple times. The SD had runs from 12.6 to 12.95.

Furthermore it's a 2.88 diff.

W123 and W126 specs are quite conservative. Most folks with properly running engines do better.

As a further measure of accuracy, one SDL runs 10.7 and the other runs 12.3............the 10.7 is faster than spec by a good margin.

These figures aren't anything special. Others on the forum have SD's that are faster than this one...........without adjusting the pump.

Freeride, what are you using to gauge 60MPH?
If it is the speedometer, have you verified its accuracy?
My 83 will do zero to what the speedo says is 60 in about 14 seconds, BUT my speedo reads 5 over actual speed.
Real 0-60 time is 17+

X2 on the check in both directions. Judging flat by eye is not as easy as most people think it is. I've done a fair amount of earth moving with diesels that do 0-6 in 12 seconds, and until you've busted out the transit, can't be sure it flat.

At 57MPH on the cluster Garmin GPS shows 60 so it's 60. But I didn't use GPS at the time of measurement because it has delay. I simply press stopwatch when needle is at 57.
Didn't check both directions, didn't know it matters that much

Hi Guys,

My Benz smokes a bit on hard acceleration. So a quick search got me to this thread. I saw where Brian has recommended a 12 psig boost pressure at 3500 rpm in 3rd gear. (Brian has already helped me on tranny vacuum control on another thread). Well, I checked my boost pressue last night and am getting 9.5 psig just upstream of the overboost solenoid. The banjo bolt and line are clean. Brian indicates that adjusting the wastegate valve should be approved with some care. Can one of you provide me with a procedure for adjusting the wastegate? I have the air filter assembly off and inspected the turbine assembly. This thing is not jumping out at me. After adjusting boost, what is the next step to addressing the smoke? Rebuild the injectors?

__________________
Larry in Mobile, AL
'83 300SD "Goldfinger" 145K Mi W126 E-617.95 T-722.3 15" Bundts

Floyd, I got some real good friends from LA
That is to say Lower Alabama.
Brian sent this link - http://www.serenitysys.com/MB/Service_Info/Turbo_Tweak/tweaking_the_mercedes_617_turbo_.htm for adjusting the wastegate, doesn't seem too hard, but I am going to try it when I can take 2~3 days to do it. Does not look like the kind of job to do before that cross country road trip, or in my case, when you wife is expecting the next progeny.
The black smoke is bound to be unburned fuel. Have you made any adjustments to the ALDA? That was where I was headed when I started this thread, and will end up there eventually, after some other overlooked procedures get attention. Does the top of the ALDA look like it has been opened? My understanding is that the ALDA increases fuel delivery during hard acceleration, and the adjustment procedure seems to be open it up until it smokes, then back it off just until it stops.

OK, the "slinky" spring removal procedure on the wastegate valve is the keys to the kingdom. Does not look too hard. Thanks much! And no, there is no evidence that the ALDA valve screw has been tampered with. In folks experience does the wastegate adjustment reduce the smoke?

__________________
Larry in Mobile, AL
'83 300SD "Goldfinger" 145K Mi W126 E-617.95 T-722.3 15" Bundts

Okay everyone keeps suggesting playing with the wastegate spring. I have the air research turbo and I read that it is harder to adj. Can't I just build a boostcontroller instead?

Thanks!

__________________
Regards,
Ian White

1995 E300 Diesel w124 OM606
2014 E550 w212 M278 biturbo

2001 BMW 740i E38 M62 (past)
1981 300SD w126 OM617 (past)