Switchover Valve & ALDA - PeachParts Mercedes-Benz Forum

Spruill · #1 03-19-2012, 09:56 PM

I've had my '84 300TD for a little over a year and am trying to diagnose some vacuum issues.

While I was messing with the lines I noticed that my switchover valve looked a bit different from others I had seen in a turbo diesel (pic #1). Has someone replaced the old turbo switchover valve for a non-turbo one?

Then, I found that the line coming from the switchover valve was going to the door lock check valve (pic #2). Is this right? I also found a golf tee plugging a line just below the door lock check valve and I thought maybe that was originally the line that was attached to the door lock valve instead.

Additionally I saw that the line from the banjo bolt on the end of the intake manifold was going straight to the ALDA (pic #3). I thought there was suppose to be a line from the switchover valve going to the banjo bolt, and the other line from the switchover valve going to the ALDA. Which brings me back to wonder why my switchover valve only has a connection for one line.

Does any of this look right? Like I said, I'm just learning about the vacuum system so I could be wrong, but none of this looks right based on other diagrams I've seen.

Brian Carlton · #2 03-20-2012, 12:31 AM

The switchover valve, more commonly known as the overboost protection valve is proper and is shown in the first photo.

However, it is clearly not plumbed properly.

First understand that there are two separate systems here. The first is the vacuum system which runs the door locks, the power brakes, and the transmission shifting characteristics.

The second is the pressure system that allows the ALDA to deliver more fuel as the engine produces boost pressure from the turbo.

NEVER shall the two of these systems meet.

The line from the back of the manifold, currently going directly to the ALDA, should be routed to the bottom of the overboost protection valve. The horizontal port at the top of the valve (currently connected to the vacuum system by a moron) is to be connected to the ALDA.

Be a bit careful when you do this and ensure that vacuum or air will pass thorough the overboost protection valve. If you plumb it properly and it's clogged with soot, you get no additional fuel from the ALDA.

The current line that goes to the top of the overboost protection valve is doing absolutely nothing and should be disconnected and plugged. I'm not exactly sure how they managed to badly configure the vacuum system to end up with a vacuum line attached there.

Spruill · #3 03-20-2012, 06:23 AM

Quote:

Originally Posted by Brian Carlton

The line from the back of the manifold, currently going directly to the ALDA, should be routed to the bottom of the overboost protection valve.

Ah, on the bottom. I didn't think to look there. I wasn't sure what was going on since I only saw one connection going to the overboost protection valve, on top of the fact that it was connected to the door lock valve.

Thanks for your help.

cho · #4 03-20-2012, 06:57 AM

hi guys

my current setup has overboost valve bypassed, but I would like to
bring it back to functional state,as it is now, the valve just seats on firewall
and I can not see the electrical connector in it.

so my question is,..if I just re-position my line to go from manifold to valve and from valve down to alda will it function at all? (without that electrical "thingy")

and how can I test valve itself for proper functionality?

cheers
ChO

.

Govert · #5 03-20-2012, 07:24 AM

Quote:

Originally Posted by cho

hi guys

my current setup has overboost valve bypassed, but I would like to
bring it back to functional state,as it is now, the valve just seats on firewall
and I can not see the electrical connector in it.

so my question is,..if I just re-position my line to go from manifold to valve and from valve down to alda will it function at all? (without that electrical "thingy")

and how can I test valve itself for proper functionality?

cheers
ChO

.

Without the electrical connection the safety valve is useless.

The valve must vent if the pressure sensor on the intake manifold is connected to ground. Pressurize the system (with a hand pump or your lungs) and connect to ground. Pressure must leak away.

cho · #6 03-20-2012, 08:26 AM

thanks Govert,

I ll have to contemplate on this one

also does the line from manifold to ALDA had to be hard plastic line (Tecalan)
as my mechanic changed that one with simple 3mm fuel hose ??

edit : 3 digit post

)
.

Brian Carlton · #7 03-20-2012, 09:14 AM

Quote:

Originally Posted by cho

thanks Govert,

I ll have to contemplate on this one

also does the line from manifold to ALDA had to be hard plastic line (Tecalan)
as my mechanic changed that one with simple 3mm fuel hose ??

edit : 3 digit post

)
.

You can certainly use the fuel hose as the complete line. However, it's not as durable as the Tecalan lines in a hot underhood environment.

I'm not sure how the mechanic replaced the line to the banjo. The part is complete with banjo bolt/Tecalan line as a complete assembly. He would have to use some type of small hose clamp on the banjo. Probably not a good plan for durability.

cho · #8 03-20-2012, 09:21 AM

Quote:

Originally Posted by Brian Carlton

.. He would have to use some type of small hose clamp on the banjo.

nope, he did not, he just humped hose on and that is it... at least I can help
myself with some small clamps as you say... thanks !

.

Brian Carlton · #9 03-20-2012, 09:56 AM

Quote:

Originally Posted by cho

nope, he did not, he just humped hose on and that is it... at least I can help
myself with some small clamps as you say... thanks !

.

Another mechanic doing the wrong job...........sorry to say. It's a pressure line and "humping" the hose in place won't work at high temperatures.

Spend the money on the correct part.

toomany MBZ · #10 03-20-2012, 03:37 PM

Mine had been bypassed when I bought it, I haven't changed anything.

cho · #11 03-20-2012, 03:58 PM

Quote:

Originally Posted by Brian Carlton

Spend the money on the correct part.

got it

MB Part #617 070 0781

.

cho · #12 03-20-2012, 04:00 PM

Quote:

Originally Posted by toomany MBZ

Mine had been bypassed when I bought it, I haven't changed anything.

yeap.yet you still have a Tecalan

.

edge · #13 06-08-2012, 01:45 PM

Can someone supply me with the switchover valve part number and the 2 mini rubber hoses that connect to it before the banjo lines? I was taking out the switchover valve to clean and the brittle plastic end snapped off, arrrggghhh! For my '85, thanks.

toomany MBZ · #14 06-08-2012, 02:05 PM

The attachments may help.

edge · #15 06-08-2012, 02:29 PM

Thank you, toomany MBZ, much obliged.