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Old 09-04-2018, 11:47 AM
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Join Date: Nov 2009
Posts: 81
sometimes it has power sometimes not.

My 93 om602 is often sluggish. On occasion, especially when thoroughly warm it has a lot of pickup. It is like night and day. I feel like its a vacuum connection somewhere that seals up when warm but not always. Ive replaced all vacuum connectors and vacuum system wide seems normal. The difference really feels like its an N/A vs Turbo sometimes. Could it be the ALDA? Waste gate actuator? where to start?

Before I start turning every stone I figured i'd ask.

Thanks guys.
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Old 09-04-2018, 12:00 PM
Diseasel300's Avatar
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Join Date: May 2016
Location: Texas Hill Country
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Your wastegate is vacuum controlled unless you've modified it to be a pressurized wastegate actuator. Make sure the vacuum system is *PERFECT* or you risk issues. Clean out the passages on the intake manifold for the boost sense line to the ALDA as well.

With some work you can convert the turbo to a pressure-operated wastegate and bypass all that vacuum crap.

Another thing that people often overlook is the ALDA module itself. If the O-rings in it are rock hard and dried out, you're losing boost to the atmosphere or into the IP itself instead of operating on the copper bellows. Replacing those O-rings makes a NIGHT AND DAY difference if they're leaking. You can test for leaks by attempting to pull a vacuum on the ALDA module. It should hold vacuum indefinitely if the seals are good.
'11 Honda Accord EX - "The Daily" 64K
'83 500SL Euro - "The Money Pit" 116K
'91 350SD - "The Diseasel Jr." 168K
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Old 09-04-2018, 12:27 PM
tyl604's Avatar
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Join Date: Feb 2008
Location: Atlanta, GA
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Does the om602 have a switchover valve? This is part of the vac system and connects to the ALDA. If so, it could be bad. Will significantly affect power; my SD would not go over 35mph when I connected my new one backwards. Switched the vac hoses and magic - all power back.
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sometimes it has power sometimes not.-1981-300sd-switchover-valve_001_001.jpg  

Last edited by tyl604; 09-04-2018 at 01:48 PM.
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Old 09-04-2018, 09:12 PM
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Join Date: Sep 2007
Location: Calgary Alberta Canada
Posts: 1,206
Unplug your maf and go for a rip around.
92 e300d2.5t
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Old 09-04-2018, 10:23 PM
sixto's Avatar
smoke gets in your eyes
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Location: SF Bay Area
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90-91 have an overboost protection switchover valve. 92-93 don’t.

98 E320 s sedan and wagon
02 C320 wagon
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Old 09-05-2018, 09:25 PM
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Join Date: Nov 2009
Posts: 81
Thank you for the replies.

From the intake manifold the pressure line is split between ALDA and to a electric module of sorts. Overfuel protection of sorts?

Anyway, I drew vacuum on the ALDA. At first it leaked but after pumping a bit it sealed up ok. Power seemed decent. So here is the question. I remember reading that the new gold style ALDA are non rebuildable unlike the old ones were. What are my options besides getting a new pump?

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Old 09-07-2018, 12:27 AM
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1987 w124 300D
Join Date: Mar 2008
Location: Edmonton, Canada
Posts: 1,539
ALDAs are meant to be removed and discarded if they start causing issues. Don't repair them, chuck it and don't replace it. Leave it off. They're a driver convenience "anti smoke" device, a nanny thing, that when if you press too hard on the pedal, you don't blow black. It's all great in theory, but when there's any ALDA issues (seals, etc) the problem shows up as loss of power. Remove the ALDA goodbye issues. When it's off, if you press too hard on the pedal you blow black. So learn how to drive by not over fueling.. get to know what the car is capable of and don't think pushing more fuel will help. When you see black pouring out the back end, that's just unburned fuel - pure wasted money.

The shut-off valve is a thing that can mysteriously rob power, if it's semi-depressed. Next time you're suffering from power loss pop the hood and note the position of the lever. Manually pull the "throttle" cable to rev the engine see if the lever bobs around. Check vacuum on the shut off circuit.
Scott McPhee

1987 300D
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Old 09-24-2018, 08:56 AM
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Posts: 81
The shutoff valve is brand new and the ALDA is leaking for sure. I’m not a fan of uninstalling the ALDA. I’d prefer to replace it if possible. Can the previous type Alda from other models be used or are they model specific?
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Old 09-24-2018, 09:01 AM
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Posts: 81
picture of ALDA

This is the type I have.
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sometimes it has power sometimes not.-img_3691%5B1786%5D.jpg  
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