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83' 300d
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343 Posts
Discussion Starter #1
So i have an 85' California 300D.

Anybody know why someone would bypass the boost pressure switch over valve (as in the thing mounted to the firewall almost behind the brake booster)???

The car feels sluggish, even though i've done a diesel purge, changed all of the filters, adjusted the throttle linkage, and done a valve adjustment. I was looking for a sooted up banjo bolt on the intake mani, but i found that my pipe routing is all funky.
For some reason, my switchover valve is still plugged into the electrical stuff, but the vac nipples have tiny little nubs on them and are plugged. Basically, the thing is plugged in, but bypassed. The clear hose on the exhaust/intake mani is connected directly to the ALDA. Any idea why someone would do this? What does this result in? Is this the causing the car to run suuper sluggish? Or... worse yet, is this causing a dangerous lean condition when in boost?
 

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1981 W123 300D non turbo, 1992 190E 1.8 <=> 2.0
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6,561 Posts
Is that the famous blue flying saucer you're talking about?
 

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1981 W123 300D non turbo, 1992 190E 1.8 <=> 2.0
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6,561 Posts
This one?



If so I can't help - sorry!

Wait for Rmac.

I only thought that mostly people disconnect vacuum lines in an attempt to change transmission behaviour - and that blue flying saucer thing often gets it in the neck (from what I have read).
 

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83' 300d
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343 Posts
Discussion Starter #6
Yea, the reason i bring this up is b/c i was following that vac diagram.

If my switchover valve is bypassed, does this cause the car to not enrichen the mixture when in boost? Or... is the valve's only function to cut intake pressure manifold signal when in overboost?
 

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1985 300D Gone 1985 230CE Perfect, 1984 300TD Driver, 1981 300TD Bad engine
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1,418 Posts
The function is to protect in case of over-boost. I have found more switchover valves that don't work that ones that do work. Yours must have failed and it was bypassed.

The blue flying saucer must be the vacuum device mounted near the fusebox on the left fender. It is for controlling the vacuum signal for automatic transmission shifting. It is found only on 1985 W123 and later diesels.
 

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1981 W123 300D non turbo, 1992 190E 1.8 <=> 2.0
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6,561 Posts
...
The blue flying saucer must be the vacuum device mounted near the fusebox on the left fender. It is for controlling the vacuum signal for automatic transmission shifting. It is found only on 1985 W123 and later diesels.
Ignore the blue flying saucer red herring - that was my fault...
 

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2001 Volvo V40
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2,954 Posts
The 85's have a different set up, yet you may be able to bypass the switchover valve, #125 in the tiny pic.
#125 is a different switchover valve, it is to change the vacuum signal to the transmission depending on the temperature of the engine:
< 50 degrees C = more vacuum
> 50 degrees C = less vacuum
 
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