Please understand that this is the first turbo-diesel that I have owned. It is a 1983 300SD.
What is all the talk about the ALDA? Is this somthing I can check?
Does it get out of adjustment? What does it do?
What is the "switchover valve"? Can I check mine for operation?

To me the car drives very well and has alot of power, and good acceleration. But I am comparing it to my 1980 300D, non-turbo.
I would just like everything to be adjusted "just-right"
I would have thought that I would feel the turbo boost more that I do. Any thoughts are appreciated.
Robert

Rob,

There are extensive answers to most of your questions in the archives. Try doing a search for "ALDA" or "ALDA adjust" and see what comes up. I'll try to give some short answers:


What is all the talk about the ALDA? Is this somthing I can check?
It's not something you can really "check", except by 0-60 times (should be roughly 13-15 seconds for your car.) If your car is slower, there may be a problem either with the ALDA or the signal to the ALDA being obstructed.


Does it get out of adjustment?
It can over the years, yes. You would adjust it as mentioned in my other post on your other thread. Be warned, though, that about 10-20% of the time when adjusting, one of the internal bladders may break, rendering the ALDA useless; and if you're REALLY lucky the car will be undrivable until it's fixed. I don't want to scare you, just let you know it's possible. Most people fiddle with it all the time, no problems.



What does it do?
It provides fuel enrichment as boost pressure rises. The turbo pumps more air as RPM and/or load increases, and the ALDA takes that signal and makes the IP provide more fuel. More fuel, more air, more power.


What is the "switchover valve"?
It is a safety valve between the intake manifold (signal from turbo) and the ALDA. If boost exceeds 1.1 bar (+/- 0.15), as measured by a sensor on the intake manifold, it will engage the "switchover valve" next to the brake booster. It kills the signal to the ALDA, which kills fuel enrichment, and saves the engine from overboost and melting pistons and such.


Can I check mine for operation?
Yes. Remove it and try to blow through it. You should be able to. If not, it's plugged. You might be able to clean it, but if not, it needs to be replaced. To check for the safety operation you remove the wire from the sensor on the intake and ground it with the ignition on. The s/o valve should "click" and when engaged, it will cut the signal to the ALDA (actually, vent the ALDA to the atmosphere through the little capped fitting on top). The sensor on the intake can be checked if you have a MityVac with a pressure gauge, you remove it and apply pressure to the hole and see if it closes (with a VOM) at 1.05-1.25 bar.


A simple test of the SOV is to bypass it and go for a drive, if you get lots more power, it's plugged. If there's no change, either it's OK or there are other problems (no/low boost, bad IP, bad ALDA, or something else major).


HTH,

__________________
Dave
Boise, ID
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