ALDA questions W124 300D - PeachParts Mercedes-Benz Forum

bfrinkus1 · #1 10-11-2021, 03:42 PM

Good afternoon! I have a new-to-me 1991 300d with 392,000mi on the clock. She was neglected by previous owner and I'm trying to find and address issues to get her roadworthy again. I'm close, but have hit a snag and need guidance surrounding the ALDA system. I have some fairly specific questions, all help appreciated!

Following an unrelated cooling system repair, I was driving her quite hard to ensure cooling system functioning properly. During the test drive, I was at 100% throttle in top gear up a long ~5% grade running ~80mph (so full boost) when there was a sudden and discernable loss of power that has persisted in all driving since. This is not fuel filters as 1.) they're pretty new and 2.) power loss was instantaneous vs the slow fade of a fuel filter.

Prior to this issue, I believe that entire boost system working properly as power was fantastic and exhaust smoke was non-existent. Now, while I still have zero exhaust smoke, but power is poor at times I should be experiencing turbo boost (unboosted power off idle is unchanged).

My hunch is that I popped an ALDA capsule. I welcome other ideas, but my questions center around this hunch:
1.) If a capsule popped is this repairable, or does the whole valve have to be replaced?
2.) If I need a new valve, where the heck do I buy one...I can't find any online!
3.) My intake needs to come off for other reason (cleaning out EGR gunk and to gain access to glowplugs for replacement and pre-chamber reaming). As long as I have it off, this would be an optimal time to replace/service/repair the ALDA. I'd love to avoid unnecessary knuckle-busting; is there a way to rough-in ALDA adjustment while I have the intake off?

Thanks ahead of time for your thoughts and expertise!
Brad

dieselbenz1 · #2 10-11-2021, 03:59 PM

Why not see if you are getting any boost by using a portable gauge? Do you know if you are still using a vacuum to control the waste gate? Alda's are rebuildable just 2 orings but they can be tested by putting on say 10 psi and it shouldn't bleed down at all.

bfrinkus1 · #3 10-11-2021, 04:36 PM

I'm a dummy, so requesting clarification:

If I put a mityvac on ALDA, it should be able to hold 10 pounds of pressure?

This car is still running a vacuum wastegate. I've modified a previously-owned w124 300d with a pressure wastegate. In that previously-owned car, the waste gate was stuck open allowing zero boost...zero boost = ran like a DOG. My current situation is underpowered, but not as underpowered as the stuck-open waste gate (as memory and the seat of my pants remembers).

Thanks!
Brad

rrgrassi · #4 10-12-2021, 02:13 AM

Check the turbo actuator. It is vacuum controlled. Loss of vacuum, opens the waste gate.
I performed the waste gate actuator change from vacuum actuated to pressure actuated on my '91.

GSXR did an awesome write up on how and why to do that.

shertex · #5 10-12-2021, 06:26 PM

You should definitely do the wastegate conversion...removes so many vacuum variables.

Remove the ALDA and plug the line to see what happens. Just use your foot to make sure you don't overfuel too much.

bfrinkus1 · #6 10-15-2021, 09:04 AM

So I removed the vacuum line from the waste gate and ziptied the wastegate actuator arm in place and performed 2 test drives; one with arm all the way out, one with the arm all the way in. I wasn't sure which would be open or closed so I did both :-).

Under test drives, I did not achieve any boost. To me, this eliminates the wastegate (or valves or vacuum controls operating the wastegate) as the root cause of my sudden power loss. A pressure actuated wastegate is on my long term to-do list, but it's taking a back seat to finding and fixing current power loss situation.

This circles me back to original ALDA questions:
1.) If a capsule popped is this repairable, or does the whole valve have to be replaced?
2a.) If I need a new valve, where the heck do I buy one...I can't find any online!
2b.) If I only need parts, are these parts readily accessible (ie generic o-rings) or are they MB specific parts and, if so, where can I source parts?
3.) My intake needs to come off for other reason (cleaning out EGR gunk and to gain access to glowplugs for replacement and pre-chamber reaming). As long as I have it off, this would be an optimal time to replace/service/repair the ALDA. I'd love to avoid unnecessary knuckle-busting; is there a way to rough-in ALDA adjustment while I have the intake off?
4.) Follow-up; anyone have an exploded view and/or parts diagram of an ALDA of this generation?

Brad

dieselbenz1 · #7 10-15-2021, 09:34 AM

http://www.peachparts.com/shopforum/diesel-discussion/373172-fix-your-alda.html

dieselbenz1 · #8 10-15-2021, 09:37 AM

On your test drive did you rev the engine past 2500 rpm?

shertex · #9 10-15-2021, 01:11 PM

Unless I'm missing something, you haven't yet REMOVED the ALDA to see what happens. Won't that help you to figure out if the ALDA is the culprit?

bfrinkus1 · #10 10-15-2021, 04:22 PM

DieselBenz1, this youtube vid was just what I wanted to better understand the guts of the ALDA. Thank you!

Also, yes, I did rev it past 2500RPM.

Shertex, I have not yet removed it. Trying to gather as much information as possible prior to teardown to make sure I know what I'm getting into. Soon!

Brad

vstech · #11 10-15-2021, 09:01 PM

Ok, you will not get any boost without fuel.
A simple open end wrench removes he Alda, and locks it to max fuel… try it.
If THAT makes no difference… change the fuel filter… they plug up instantly too…

CanadasHistory · #12 10-19-2021, 02:22 PM

Quote:

Originally Posted by vstech

Ok, you will not get any boost without fuel.

Yes they will, they won't get more power from it.