Could hook up a temporary boost gauge to check out if the turbo is involved. Of course feeding it back into the cabin.

Your symptoms sound exactly like when my waste gate was frozen closed and the over boost protection cut in. I would lose power, and if I let off the accelerator pedal, it would return. Once I put a boost gauge on it, I could see that under a little more than half throttle, at about 2,500 rpm, boost would get to about 15 lbs and suddenly drop to about 6.

What does your gauge do right before and as you lose power?

Freeing up my waste gate was simple with some penetrant. I worked it lose until the whole valve slid out where the plate with four bolt/nuts is. You need to take the diaphragm off to do this, and can inspect it at the same time. With the carbon cleaned off the valve and hole it goes through, it slides open easily and I have no more loss of power from boost cut off.

————
1985 300TD

I took the ALDA off and tested it. It holds no vacuum nor pressure. Is it really suppose to? By the way, what's inside the ALDA make no sense to me. I was expecting a rubber diaphragm I guess. Those engineers.....

The purge return fluid was clean looking last time I did it.

Again, the turbo feels perfect. Tight and smooth.

This is a manual transmission so no issues there are possibly related.

It's not doing what you had happen tdhawk. I don't lose power. I never have it until later in my revving. It can't be turbo related in my opinion. The response when I do get the power bump is just too quick plus I'm monitoring the pressure (with my in-dash turbo gauge) and nothing out of the ordinary happens there. I think there's a 95% chance this is fuel-only related.

I don't have an overboost protection circuit on this engine (never had one).

I'm testing it tomr., running without the ALDA to see if there's any changes. And yes I plugged the manifold with the required M8 1.00 pitch bolt. (not many of those laying around)

The ALDA has 2 seals in it. There is one on the shaft where it connects to the IP and there is a perimeter seal where the 2 halves screw together. When working properly, the ALDA should hold pressure and/or vacuum, but over 30+ years the rubber dries out and fails.

The ALDA contains a set of copper bellows that compress as the manifold pressure rises and lift a plunger in the IP to enrich the fuel. If the pressure in the manifold is building, but the ALDA is leaking, you will get a skewed fuel enrichment curve. When it is working properly, you can't really even tell when the ALDA begins enrichment, it should be a very smooth transition when the turbo starts spooling up.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Sounds like your car is in far from factory condition. Turbocharged engine, but manual transmission. New fuel tank - why did that happen? ALDA doesn't hold vacuum or pressure and the screw was backed all the way out and removed - that tells me that your ALDA is probably destroyed.

I'd be looking for a good used injection pump with unmolested ALDA at this point.

I'd also be taking a real hard look at the turbo-charger and waste-gate operation.

Is this an OM617? OM617 valves should be adjusted annually and every 15k miles, whichever comes first.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

How does it drive with the alda removed?

__________________
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"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

SOLVED!

First I wasted my time and money and got a 10x2.5mm O-ring for the ALDA and it did indeed hold a vacuum but I noticed the height of the plunger/shaft seemed off before and after, after looking at my other one while performing the repair. I pushed down on it with a screwdriver and noticed a lot of resistance, as if it had pressure in it, but there was none.

I got the other "good" ALDA I had from my screwed up inj. pump and noticed there was definitely a height difference in the plungers at rest. The one I was running seems to have had some issue with the screw, as you can see. This was causing a ton of irregular behavior apparently. The brass looking one is the bad one. It's mm's higher at rest.

I tested my good one but it wont hold a vacuum either. The screws on it are the tightest I've ever encountered. I tried my hardest, to the point of hurting my hand, as well as using an impact driver, and they won't move.

I left the ALDAs off and thought I should test drive it finally. On start-up I noticed immediately that the idle was slightly higher than it was, for whatever reason, so I had some confidence something was different. I took it very easy at first to heat the engine up a little and then got out to the main road and laid into it. WOW!!!!!!!!!!!!!!!!!!!!!!!! I have my engine back!!

I mean holy sh**! I swear I have 30hp+ more than I did, and at all revs.! My boost gauge slammed up to 11psi in no time. I may have one of the strongest 617's around... no kidding.

For TWO YEARS I have suffered with this issue in some way and it was truly a source of depression. If only I had taken this piece of crap ALDA off long ago I'd have had a much better life.

I did not notice any massive smoke cloud with the ALDA off. I was on a road where the sun would have back-lit it but still didn't notice anything obvious. I'll get someone to follow me soon and see what they say but for now I'm leaving it off and enjoying a very healthy engine.

This painful lesson shows how important it can be to simply take the ALDA off when looking into suspected problems with it. I was under the impression, like many others it seems, that backing the screw out all the way was the same thing as taking it off. That is definitely wrong. I also believe that these things are so old now that many may not be working correctly anymore. How many other motors are under powered due to these things?

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Glad you figured that out, I'll be curious to see what impact this has on your fuel consumption and soot load in your engine oil.

For the record, backing out the screw too far will cause the ALDA to break internally.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

From reading many guys posts who have removed it, it sounds like it causes few if any issues.

It behaved this way before I backed it out all the way. Either someone had already done that or it was really messed up overall. Either way, good riddance to it.

I've also heard that removing the Alda does not affect mpg hardly at all. It just allows more fuel if u need it, u don't have to stomp on the gas all the time tho.

It's great to have a solved thread on here. Does the forum let u edit your title to ad "SOLVED" to it. So other forum members and people doing google searches can see it?

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Yeah I rarely step down on it like that anyway. From what I can tell with my vacuum/air pump is that the other ALDA wasn't working either, but in a different way, and I drove that thing 1000's of miles for years that way and it ran perfectly and very strong all those years.

So many people have removed them for so long without reports of issues that I can find. I'm not convinced its needed other than to comply with original specs. After all, it's a mild emissions control device and like most of those, when they wear out or break, cause even more emissions due to inefficiency and operator work-arounds.

I tried to edit it but no, it won't let me. You can see where I added SOLVED to the original post subject which I thought was the headline but apparently not.

It is also part of a safety system, so you don't melt your pistons if your turbo waste-gate fails in the closed position and turbo pressure drives the combustion temperatures too high.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

I prefer fact-based decisions. I'd like to see some data on engine oil soot load and MPG, baseline with before removal data, before I'd do it to my car.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC