Why?

The only reason that I can fathom is the loss of overboost protection.

Driveablility is significantly enhanced for every member that has removed the ALDA. In fact, it's so dramatic, that I don't believe that anyone can bring themselves to put the damn thing back on!!

I agree 100%. I love how my engine runs without it and I will never put it back on.

How/where would you connect a boost gauge, to monitor the boost? I think it would prevent further damage to just take the foot of the pedal when it reaches 15 - 16 psi.

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'99 S420, 155k
'91 VW Vanagon GL, 150k
'85 VW Vanagon GL, 120k
'82 VW Westy, aircooled, 165k

There is already an overboost switch mounted off the intake manifold which cuts fuel at boost pressure exceeding 17 psi, besides the standard switchover valve overboost protection that communicated with the ALDA.

A boost pressure gauge may be installed via a T-fitting assembly branching from the intake manifold boost pressure orifice from where the original switchover valve drew its pressure signal from.

Hmm, there must be an easier way. This switchover valve at the intake manifold converts the pressure it measures into an electrical signal, right? Does anybody know, what kind of a signal this would be? Is that a simple switch which closes a circuit when critical pressure is reached or does it work with changing resistance depending on pressure? If it is a simple switch, one could just connect a warning buzzer or light to it, correct? I'll go to my car now and do some testing.

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'99 S420, 155k
'91 VW Vanagon GL, 150k
'85 VW Vanagon GL, 120k
'82 VW Westy, aircooled, 165k

According to the service manual (wiring diagram) the switch closes a circuit to ground at 1.2bar (17.5 psi). So if I just connect a warning light / buzzer to + and to the switch, the light / buzzer will come on at 17.5 psi, correct? Any comments, ideas, corrections please?

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'99 S420, 155k
'91 VW Vanagon GL, 150k
'85 VW Vanagon GL, 120k
'82 VW Westy, aircooled, 165k

The switchover valve on the firewall reacts to a pressure transducer on the manifold. When the overboost setpoint is reached, the valve closes cutting the pressure signal from the manifold to the injection pump. This reduces fuel enrichment to the point that there is insufficient exhaust flow for significant turbo boost.

There is no manifold pressure sensor in an 87 SDL other than the overboost sensor.

The pressure transducer on the manifold sends a ground signal to the switchover valve at the setpoint. I doubt you'll ever see that if you have a working wastegate actuator. It cannot be easily modified to be boost gauge.

When I hook up a boost gauge, I run a hose into the cabin through the door. The seals are supple enough to not crush the hose. Obviously a temporary measure. For a permanent boost gauge, run a hard plastic line through the firewall. There are extra spaces in the grommet beside the brake booster. The line comes out near the brake pedal pivot on the cabin side.

Sixto
93 300SD

Bump for recent question about how to adjust the ALDA... please note that the same information applies to the 602 engine.

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Dave
Boise, ID
Check out my website photos, documents, and movies!

Nope. Although that is a valid concern for people without a boost gauge.




It depends on the engine in question. If your injection pump is so lean that you can remove the ALDA entirely and never see smoke, ever, it's probably ok to remove it (but you're not fixing the root problem, an out-of-adjustment IP). On my engine, when the ALDA is adjusted too rich (or removed), it will smoke, and also screws up the tranny shifting as well... you're using a lot less throttle to get the same power, and the VCV on the side of the IP only knows how to modulate trans vacuum based on throttle position. So you can end up with flaring, and also early upshifts as well (since the bowden / kickdown cable is not being pulled as much).

Bottom line - as I stated earlier, I'm all for adjusting the ALDA, but I do not condone removal on a 602/603 engine except in unusual circumstances.

I can vouch for this behaviour... I'm seeing it exactly. Removed ALDA on 603.96 and VCV interaction is as described, and tranny responds as described. Yes, sans-ALDA more off the line punch, and I'm drunk on it. I do see more smoke at idle so I think I'm burning a little richer than needed.

I'm thinking of putting the ALDA back on but shimmed up, or not. Still drunk on power. Maybe just try adjusting the bowden cable instead to "re-train" the tranny where the shift points should be w.r.t. throttle position.. I know the problem will remain with vac-too-high because of low twist on the VCV... which means shift points might be better (thanks bowden) but still softer / flaring due to vac out of whack. That's why I tried advancing the VCV too much, it worked a little but has this nasty tendency to reduce full throttle position -- another story.

So what I want is a "bleeder tap" where I can dial in 0 to 10 inHg loss, to introduce less vacuum going from the VCV by a fixed amount.. and tune vac down that way. I played with T-ing in orifices at different points...

But now we're way off topic of ALDA removal.

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Cheers!
Scott McPhee

1987 300D

What's the right amount to shim an ALDA?
At maximum seat-of-the-pants but with "no black smoke".

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Cheers!
Scott McPhee

1987 300D

I understand that without ALDA, your factory overboost protection is gone.

People have talked about putting a buzzer on the dash hooked to the 1.2 bar overboost switch, no answers offered. I had the same thoughts.

The big fear is a stuck wastegate, right? Causing overboost. Suppose the plastic pipe controlling the wastegate melts or falls off. No pressure input, car has no sense to regulate boost, no wastegate control, and pop goes your engine.

Is there not a direct way to connect 1.2 bar switch to some aftermarket wastegate controller with a directly connected actuating arm attached to the wastegate (as a secondary puller) that yanks it open that 1.2 gets hit?

Can we mount a blow-off type valve on the pressurized intake somewhere (I see a couple nice potential spots) that simply cannot hold back more than a preset or dialed-in 1.2 bar? Maybe put a couple of these on ... in case one fails to relieve.

Or for that matter, an electrically activated valve that opens to vent the intake to atmosphere when the stock 1.2 bar switch closes?

__________________
Cheers!
Scott McPhee

1987 300D

Lack of overboost protection is not the end of the world as long as you catch it soon enough. I would keep a boost guage installed.

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That should be the first thing done before messing with any of the engine settings.