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  #1  
Old 10-31-2007, 12:11 PM
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The ALDA - My thoughts

I like many have backed of the screw to tweak the ALDA. After opening mine, I am now having second thoughts. I think it might be a quick fix to getting more power, but at the expense of it doing what in part what it was designed for, that being changes in altitude.

The ALDA pushes a pin in the injector pump. Changing the screw location effects how much the pin is pushed in. Changing the screw location also changes the location of the aneroid capsules inside the ALDA which I come to think will impact the functionality at different altitudes.

There are factory spacers available to raise or lower the ALDA mounting to the IP, which would alter how much the ALDA pushes the pin.

By using the spacers the pin pressure changes without changing the location of the aneroid capsules.

SO now the question is.... what is the factory the method to get the aneroid capsules back to the proper location?

Don

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  #2  
Old 10-31-2007, 12:41 PM
ForcedInduction
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The screw and spacers do the EXACT same function.

There is no factory location, that has to be determined with the pump on a tech bench. Just turn the crew or use shims until you get little/no smoke when you mash the throttle from a standstill with a warm engine.
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  #3  
Old 10-31-2007, 01:30 PM
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I don't agree.

It maybe that at a constant elevation it will improve performance, but if one drives in different altitudes, the ALDA can't operate/give the intended result as the capsules have been moved as a result of the change in pressure by adjusting the screw.

The screw alters the location of the aneroid capsules within the ALDA and therefore not only the current fuel enrichment, but how and when it will function at different altitudes. It changes the fuel enrichment by pressure and not by the height of the ALDA

Changing the spacers changes the location of the ALDA to the IP and therefore either increases or decreases the pressure on the pin by ALDA height rather than by pressure.
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1983 300SD 272,000 Miles "Aristotle"
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1994 BMW 530it
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  #4  
Old 10-31-2007, 01:39 PM
ForcedInduction
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The ALDA automatically adjusts for boost pressure AND altitude. Once you set it right, it will compensate for boost and altitude changes.

Turning the screw and changing shims do the EXACT same thing. The shims are a course adjustment and the screw is fine adjustment.
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  #5  
Old 10-31-2007, 01:50 PM
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Attached is official MB method to remedy sluggish acceleration (turn the screw, NOT add shims). This is from the service manual.

Well, the file is slightly too big to attach, I'll see if I can reduce it...

Uhhg. At least it is still legible.
Attached Files
File Type: pdf ALDA_adj_reduced.pdf (18.0 KB, 306 views)
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Last edited by Maxbumpo; 10-31-2007 at 02:25 PM.
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  #6  
Old 11-15-2007, 06:16 PM
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I took it apart, cleaned it and adjusted it CCW 1/4 turn at a time, from the point of being to far CW (intentional) until I could feel a significant change and then went 1/4 more. Because so many different things were done at one time, I don't know the difference (before and after) the cleaning and adjusting.
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  #7  
Old 02-26-2010, 04:02 AM
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There are 2 aneroid capsules in the ALDA. FSM says ALDA compensates for both altitude and turbo boost.

To compensate for altitude (less air), I suppose you want less fuel. For an ALDA to do this, it must force the pin on the IP down a bit.

To compensate for boost (more air), you want more fuel. We all know allowing the pin to rise will accomplish this (by shimming).

I'm trying to determine a failure mode. And this leads up to my question: Does anyone know what the internal pressure of each aneroid would be? At sea level, would one be under positive internal pressure the other capsule sealed as a vacuum, or negative pressure? They both positive, both negative, one neutral...

In other words, if you stuck a pin into an aneroid capsule to "pop" it.. would the capsule expand (get fatter) or contract (get skinnier)?

I have a theory at least one of them gets fatter. Your theories welcome...

Why? my car lost all of its low end grunt literally overnight. I suspect ALDA (again), and have played around with shimming before, and the current gutless symptoms are very much the same as what I experience pre-ALDA adjustment a several months ago. (I shimmed versus screwed my ALDA, and adjusted it to a sweet spot of no-blowing black but definitely improvement to off-idle pre-boost conditions). This seems like an ALDA issue again.. just wondering if a seal or aneroid just "popped" due to fatigue... overnight.
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  #8  
Old 02-26-2010, 04:15 AM
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Thank you wikipedia, it led me to this:
http://www.enotes.com/how-products-encyclopedia/aneroid-barometer
and quoted from there:

Design

Product design for an aneroid barometer involves a careful analysis of the contracting and expanding properties of the aneroid capsule, design of the temperature compensation system, and mechanical design of the linkage between the aneroid capsule and the sweep indicator.
The aneroid capsule is very thin, hollow, and usually shaped like a bellows. Most of the air is removed from the capsule so that the contraction and expansion of the capsule is strictly a function of the elasticity of the capsule and any of its supporting springs. Leaving air in the capsule would induce non-linearity into the capsule response. As the capsule contracted, if there were any air left, the air pressure in the capsule would rise, which would make further compression of the capsule harder. The barometer designer calculates how much the aneroid capsule will expand or contract under the expected range of pressures the barometer will be subjected to. Based on these movements, the designer specifies the linkages that will translate the movement of the capsule into the movement of a sweep indicator on the barometer face.




and





The aneroid capsule

  • 5 Thin sheets of copper/beryllium metal (around 0.002 in [0.05 mm] thick) are stamped into the two halves of the aneroid capsule. The stamping dies are designed to leave a knife edge mating surface where the two halves will be joined.
  • 6 The individual aneroid components are electron-beam welded. Electron beam welding requires that a concentrated stream of electrons be generated and focused on the joint to be welded. As the electrons collide with the part, the kinetic energy of the collision creates heat resulting in the fusion or melting of the two pieces to be joined. Electron beam welding can only be performed in a vacuum (because the air molecules would intercept the electron beam) which is very convenient as the aneroid capsule must also be free of air. Electron beam welding is performed by automated robot welding machines because a human welder could not provide the degree of accuracy needed to join the parts without damaging them.

So, yes, it looks like a popped aneroid expands. And it also suggests both aneroids in the ALDA are under negative pressure.

And when one pops, the IP pin gets pushed down... and you get a dog.
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Last edited by scottmcphee; 02-26-2010 at 04:21 AM.
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  #9  
Old 02-26-2010, 10:27 AM
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Quote:
Originally Posted by scottmcphee View Post
And when one pops, the IP pin gets pushed down... and you get a dog.
Whoa dude. Is this something that can be checked easily? I've got a dog off the line and then fine.
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  #10  
Old 02-26-2010, 10:39 AM
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Just remove it and smoke like a chipped Cummings.
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  #11  
Old 02-26-2010, 12:22 PM
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^^^ X2 What he said.

I took the alda off my '87 300D & it made ALL the difference in the world. Smokes some on acceleration, but otherwise fairly clean. You just have to watch your right foot & keep it out of it. It is also a good idea to install a boost gauge if you do this.
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  #12  
Old 02-26-2010, 12:55 PM
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"It is also a good idea to install a boost gauge if you do this."

I think an EGT gauge would be more crucial...
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  #13  
Old 02-26-2010, 12:59 PM
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Quote:
Originally Posted by dagObx View Post
^^^ X2 What he said.

I took the alda off my '87 300D & it made ALL the difference in the world. Smokes some on acceleration, but otherwise fairly clean. You just have to watch your right foot & keep it out of it. It is also a good idea to install a boost gauge if you do this.
Actually you really need an EGT gauge, with the probe pre-turbo. If you are seeing black smoke that is unburned fuel. Unburned fuel means high EGT's, always. You are now literally playing with fire. Yes it can be easily moderated with your right foot but without an EGT you are flying blind and it is engine damage COULD be right around the corner. But you'd never know without the gauge!

RT

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