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  #1  
Old 03-21-2010, 10:49 PM
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ALDA, Overboost Protection Relay confusion (84 300SD)

Okay, so I've spent all afternoon looking at the forum, reading different posts relating to the ALDA system. I saw the ALDA boost system service article on Dieselgiant's page. This link on the forum was also very informative.

Russ refers to what is apparently called the Overboost Protection Relay (OPR) as the "switchover valve". My problem is that I can't find the OPR. Does it look different on a w126 than it does in Dieselgiant's photos (which I assume are of a w123)? Where is the OPR located on a 126?

See attached photos. Is that plastic device the OPR? If so, it looks like it has been disconnected (by PO). Does that mean the ALDA has been disabled? There is still a transparent line going from the ALDA to the banjo bolt on the back of the intake manifold.

I'm not interested in removing/disabling the ALDA (if it hasn't been already), however I'd like to clean the banjo bolt just to get any gunk out of it. Do I just clean the banjo bolt on the back of the intake manifold? What about the one that goes into the ALDA?

My car was originally purchased in CA, so I assume it's the "California model" as opposed to the Federal model. Not sure if this makes a difference with regards to ALDA.

My car runs pretty well, and pretty much all maintenance is done by my independent mechanic. I've done diesel purges on it and other minor items (replacing fuses), however it makes me a little bit nervous to start messing with or modifying stuff that may just cause me problems down the line.

Any insight would be greatly appreciated...
Attached Thumbnails
ALDA, Overboost Protection Relay confusion (84 300SD)-p1030520.jpg   ALDA, Overboost Protection Relay confusion (84 300SD)-p1030521.jpg   ALDA, Overboost Protection Relay confusion (84 300SD)-p1030529.jpg   ALDA, Overboost Protection Relay confusion (84 300SD)-p1030525.jpg  
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Old 03-21-2010, 10:54 PM
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yup, that's it. and your alda is not disconnected, just the relay is. so you have alda boost, but no overboost protection.
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Old 03-21-2010, 11:39 PM
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Originally Posted by vstech View Post
yup, that's it. and your alda is not disconnected, just the relay is. so you have alda boost, but no overboost protection.
Thanks, vstech! What's the benefit of just disconnecting the relay? Do you think I should have it reconnected? I don't really see where the lines coming out of the relay would go...
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Old 03-21-2010, 11:44 PM
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see the black line on the plastic line coming from the alda? take that off, and separate the two plastic lines with the overboost relay.
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"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!
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Old 03-22-2010, 12:19 AM
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see the black line on the plastic line coming from the alda? take that off, and separate the two plastic lines with the overboost relay.
I didn't see the black plastic line coming from the ALDA. I'll have to take another look... Thanks again.
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Old 03-22-2010, 09:14 AM
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in your picture, the whitish plastic line attached to the alda is coupled with a black rubber hose. remove that coupling, and use some rubber hose to connect the two whitish lines to the OBR. that's what I meant, if I was unclear.
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Old 03-22-2010, 12:58 PM
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Originally Posted by chrisbus View Post
Thanks, vstech! What's the benefit of just disconnecting the relay? Do you think I should have it reconnected? I don't really see where the lines coming out of the relay would go...
That switch over valve may have malfunctioned, hence it's been by passed. The turbo has a waste gate too, so it's a bit redundant.
What makes you want to hook it back up?
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Old 03-22-2010, 01:03 PM
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That switch over valve may have malfunctioned, hence it's been by passed. The turbo has a waste gate too, so it's a bit redundant.
What makes you want to hook it back up?
I don't necessarily want to hook it back up. I just don't want to take the risk of eventual engine damage by having it bypassed.

Do you think it would still benefit me to clean the banjo bolt at the back of the intake manifold?
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Old 03-22-2010, 01:08 PM
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If clogged up, you should clean it out, as you won't get the proper signal.
An MB mechanic, when he saw mine bypassed, mentioned many folks do that and it really isn't a problem, as there have few if any reports of that causing an engine failure. These engines were designed robustly and you don't make enough boost to hurt it either.
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Old 03-22-2010, 01:14 PM
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If clogged up, you should clean it out, as you won't get the proper signal.
An MB mechanic, when he saw mine bypassed, mentioned many folks do that and it really isn't a problem, as there have few if any reports of that causing an engine failure. These engines were designed robustly and you don't make enough boost to hurt it either.
Okay, thanks for your input. That makes me feel better. I noticed that Dieselgiant says to use brake cleaner to clean the banjo bolt. I've read other posts that say to use carb cleaner. Do you know if there is a difference?
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Old 03-22-2010, 02:33 PM
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No real differance, they are both fast drying solvent sprays. Brake cleaner may have a little more umph when dealing with grease is all. Dont be afraid to soak it when use are spraying.
Hope this helps
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Old 03-22-2010, 02:54 PM
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No real differance, they are both fast drying solvent sprays. Brake cleaner may have a little more umph when dealing with grease is all. Dont be afraid to soak it when use are spraying.
Hope this helps
Thanks!
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