BOOST & A Bunch of Bad ALDAs (& "disabled EGR melted that SD's engine")
 

Spent the entire day on this ...
The whole thing began with me noticing that my 82 was lacking in the boost department compared to the 84 that I sold which had neck snapping boost and thinking I perhaps could turn it up somehow. I scoured the archives and followed the easley procedure as well. I haven't got near the turbo yet...
I cleaned the banjo bolt fitting on the back of the intake manifold to the boost bleed valve. 10 lbs. of boost in the line. Hooked up the pressure gauge to the line going to the ALDA from the bleed valve, 0 psi, found I had a bad valve. Before I went and found myself a new valve I bypassed it and plugged straight into the ALDA, I figured I'd get my boost now but no change in performance. (Though I *did* check my 0-60 and it's at 16 secs.)
Scoured the archives again and found posts suggesting my ALDA may be bad and how to check it: pump it up to 15 lbs and see if it holds. I tested four that I found at wrecking yards and they all were no good. Stopped by a repair shop/dismantler asking for one and the guy wanted to know what I thought was wrong. He claimed that the ALDA had no function except at altitude. From what I had come to understand through all the ALDA posts I've read is the ALDA enriches the fuel according to the boost. (Also we all know adjusting it can take out the turbo lag...) He also looked under my hood and noticed the EGR lines were disconnected (haven't got around to installing the block off plate yet) and he told me it could be causing performance issues (!) He also said "You see that SD over there, we just got done re-sleeving the block and replacing two pistons. The owner of the car didn't want to spend the money replacing a faulty EGR valve so he stopped up the line with a BB. Within 6 months the engine melted. The EGR valve sends cooler (than compression chamber?) exhaust gases across the valves to help cool them down a little. If you sent fresh cold air the valves would warp."
Shows you how little even Mercedes mechanics know! He *did* go out of his way to try & help me but he sure seems to be missing something. (Another dismantler/repair shop I talked to insisted the ALDA was for adjusting the idle)
So anyway is the ALDA integral to boost or what?

I wonder how all those 1979 300SD are doing on the road? Why have they not melted after x00K+ miles?

From what I understand the ALDA enrichens the fuel across the board. That is why boost lines run to the ALDA. As the boost increases so does the need for fuel.

The alda device is essential as I found out. my 124's alda had a rip in the seal and over time I noticed quite a drop in boost. Not until someone on here suggested it, did I even think to check to see if it was leaking down. Swapped it out with one from a 617 (same part), boost was restored.

The EGR only slightly reduces the combustion chamber temps to reduce NoX. However when you reduce NoX you increase CO2. They are diameterically opposed, raise one the other lowers.

Now he says you will warp your valves with fresh air. Hogwash! What about the Cummins it does not have EGR. I dont see any warped valves in them. Having the ERG disabled will not hurt your valves. Also cars ran for 50 years with no EGR. Hmm.....

The ALDA on non-turbos is for altitude compensation. On the turbos it's there to regulate fuel in correspondence with the boost pressure. It other words it IS needed for the turbo charged engines.

You can stop right there as far as condemning the ALDA. You must determine why you have no boost prior to adressing issues with the ALDA. Even if the ALDA is non-functional, the engine should develop about 5 psi of boost if everything else is working properly.

When you "pumped it up to 15 lbs.", explain how you did this. The ALDA requires pressure. You can't do it with vacuum.

You are correct. The guy has his head up his a$$.

Total and complete BS. The EGR will lower the exhaust temperature slightly, but, it is normally shut down for maximum performance at full power, so, EGR could never be the culprit for melting pistons.

The mechanic is a moron. I would avoid this mechanic at all costs.

I would bet all of those "bad" ALDA's could be repaired by a simple resealing.

i *had* boost from the intake manifold to overboost sensor switch behind the brake booster; no boost from there to the ALDA - got myself a new valve at the wrecker's and now there's pressure on both sides.
i pressurized the ALDA with a gas line tester fitted with a 1/4" barbed hose to 1/2" NPT connection and a bicycle pump. (i really need to get myself a mityvac...) on both ALDAs I have i can hear air escaping at the ALDA.
i was surprised that so many of the ALDAs i tested failed to hold pressure. i figured surely it wouldn't be hard to find a replacement... i wonder how many 917s are out there that are lacking boost power from a leaky ALDA.

yep, it's amazing to me how many "mechanics" know just enough to be confused... i'd never have any mechanic work on my car unless he is in line with what i read here. i guess it just surprises me when i know - ok i don't really *know* it so much as i've read it here which is why i can't quite hold out in a debate - more than a mechanic. i only knew very roughly the function of the EGR but you all say to get rid of it and so it's done...
Thankful for all the help & support served here daily...

FWIW...

GM's Duramax now has EGR made it slower along with a cat. Remove them both, performance is better than the previous LB7 motor. Slower how? Full pressure isn't coming from the exhaust manifold to the turbo... so they boost a tad quicker w/o EGR.

EGR wasn't on them from '01-04. Just '04.5+ when the LLY came about as I recall.

The ALDA does not need to hold pressure for proper function. It's internal seals are probably not all that tight so air will bleed across them. The engine has more than enough manifold pressure to overcome a small leak in the ALDA. So, if you can pressurize the ALDA and it leaks down in 10 seconds or more, it will be perfectly fine on the engine. It may even be OK if it leaks down in 5 seconds. It all depends on the flow rate through the 4mm Tecalan lines. If the flow rate is much greater than the leakdown rate, there will be no effective drop in the pressure to the ALDA.

Brian, thanks so much for clarifying that point.
My ALDA does leak down from 15 lbs but over 15 or 20 seconds. I can *finally* get over that... :rolleyes2
Next step is adjusting my wastegate and seeing if that makes a difference in the boost. To test if i'm going to get anything out of the adjustment I'm thinking to follow the suggestion in another thread and temporarily pinch off the wastegate hose (with a pressure gauge hooked up into the line so I can watch boost pressure while I'm driving) and see if that does anything.
As I mentioned earlier, I'm trying to get this turbo to spool up like the one on the 84 I had. Is turning up the wastegate the only turbo adjustment?

If the turbo is functioning properly and is not damaged in any way, the only thing controlling boost is the wastegate. So, if you pinch the wastegate hose, in theory, the wastegate cannot open.

However, if the wastegate valve itself is not seated for any reason, then it allows bypass of exhaust gas and may limit boost. This is a rare occurance, AFAIK.

If you pinch the wastegate hose and get boost that climbs over 11 psi, then you know the wastegate spring needs adjustment.

Be careful when you drive it with a pinched wastegate hose. Watch the boost carefully. It will climb pretty quick if things are working properly.

I seconf that....I had a boost controller on my W116 and I thought I had it cranked down enough but it still went up to 20 psi in the time it took me to pull my foot off the go pedal.....that was in about 50 feet.....so yes it happens REAL fast.

Road test your theory to feel it in the seat of your pants. Buy the Mityvac and run a line from the ALDA into the passenger cabin. Pump up the ALDA with the Mityvac as you are driving to see if it makes the difference you are looking for.

BTW, the EGR mechanic is a buffoon.