Overboost Protectiion Valve - PeachParts Mercedes-Benz Forum

vwnate1 · #1 02-12-2016, 11:41 PM

On my 1984 W-123 OM617 .

Is it supposed to be closed when the engine is off ? .

I can't blow through it , by passing it makes the engine have way more power .

TIA ,

mach4 · #2 02-13-2016, 12:29 AM

The overboost protection valve normally is open to the ALDA allowing additional fuel as boost builds. If boost hits the limit, the valve dumps boost pressure to atmosphere which reduces fuel to the engine by making the ALDA see a lower pressure and thus dropping boost pressure to a safe level.

It should never hit the limit pressure unless something is seriously wrong.

vwnate1 · #3 02-13-2016, 01:31 AM

Thank you , that's exactly what I thought .

I wonder if I can clean it....

Simply by passing it seems wrong to me .

vstech · #4 02-13-2016, 04:46 AM

it's a common location for soot to collect... brake cleaner spray is your friend...

yuke · #5 02-13-2016, 07:54 AM

Oh I get it fully now as when tne nipple on my opv or also called switch over valve broke and my line came off on a long highway trip I could not go over 60mph. and had a lot of semis blowing their horn at me. It took me awhile to figure it out as the symtoms seemed like clogged fuel filters and I figured if the line was unhooked it should still work just as the valve was bypassed but now I understand that the alda needs the boost pressure signal from the turbo in order to operate just being unhooked lose is not the same as bypassed connected. On a long trip this failure could leave you in a bad situation if you are not awhere of this. Next time if it happens I will know exactly what to do. I am going to check my boost pressure yet as my 0-60 time is no where near the 12-15 sec. area it is more like 45 sec. even though I can easily cruise at 85mph. Just takes me awhile to get there on my 617 85 300sd. And I would like to add I think there is either a rubber washer or an o-ring in the alda that can tear or leak and that would give you a sluggish car also correct me if I am wrong. I did see a you tube vidio 1 time of how to repair it.

vwnate1 · #6 02-13-2016, 09:07 AM

This is what I figured .

I have a brake job (new calipers , flush and bleed fluid) to do on a W-126 to - day and I was thinking I could use some Foo-Foo can cleaner and the snorkel to clean out any accumulated carbon .

Yuke , yes , you're correct , once anything blocks the free flow or intake manifold pressure from the ALDA valve engine performance suffers at all speeds and loads .

If you have anOM617 , remove and clean the banjo bolts on the hard plastic lines leading from the rear of the intake manifold to the overboost protection valve and also the banjo bolt at the ALDA proper .

A quick test it to disconnect the line at the ALDA , even at idle there must be some pressure and as you hold it against the ALDA @ idle, the engine's speed will change as it senses the minor idle pressure .

The OM603 engine has a nipple , it clogs with soot , I just cleaned this on my Brother's '87 300SDL yesterday as we were chasing parts , I got pressure so I by passed the overboost valve as a quick test and revved the engine , I got immediate faster throttle response and when we drove it up hill ZOOM ! as mentioned , the power fades away bit by bit as the air flow slowly gets obstructed .

I can hardly wait to test it on the ' grape vine ' leading out of o. Cal. ~ my Brother drives far too slowly , he never exceeds 65 MPH , I like to occasionally touch 125 MPH to blow out the accumulated carbon .

toomany MBZ · #7 02-15-2016, 07:57 AM

That valve was bypassed when I bought the CD 12 years ago.

vwnate1 · #8 02-15-2016, 08:34 AM

It is now by passed on two of our Mercedes' but I don't think this is wise , as soon as I can I'll clean the valve out and re connect it .