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I have been trying to figure out why I only get around 13psi of boost on my SL65 AMG.
I read through as many posts as I could find on the subject. I figured I'd start with crimping off the wastegate vacuum line to see if the boost would go up. No luck still 13psi.
Next I tried pressurizing the system to check for leaks. I found one on the back of the engine. There is a plastic fitting that goes into the manifold down below the intercooler fill location. There is a part that slides in and out some and rotates. The part that slides in and out has a hole in the middle. Not sure what this is. Does anybody know? I don't want to start trying to remove it and break it without knowing how it should come off.
Also how big of leak does it need to be to limit boost that low. It's not a big leak but it is a leak.
Thanks to a post that DUDMD did a few years ago I figured it was the rear manifold cap which he had a leak as well. So I did what he did and put a cap over it.
A quick hello and pile-on to this. I just purchased a low mile 09 SL65 and coming from the Supra & 911 turbo communities, step 1 in the mod process was a boost leak check. Sure enough, after capping the turbo inlets and pressurizing, I was only able to build ~6-9 psi with a massive leak out of this plastic cap at the rear of the intake manifold. Samco silicone cap ordered from the UK. Hope it's the right size! Will update when I know for sure.
Boost leak test DIY to follow. My hunch is that many of these cars may be plagued by this one...
That rear piece connects to the power brake booster and supplies vaccuum to the brake booster. DUDM5 got rid of his whole setup and has rear mount so I do not know what he did to supply vacuum to the booster. (i do not know what he did though).
As for that rear piece, I have dissected it and replaced with a weld on bung. The nylon tube that goes into that rear port has an o ring for sealing. You can replace this easily but need to dig the o ring out from inside the black fitting connected to the intake manifold (not easy I guess with manifold on car). BUT, there is also a rubber seal inside between the black fitting and the aluminum manifold. It is green (might be viton) and flat. The problem is that this fitting is not for sale individually from Mercedes. The black fitting has a locking ring that prevents it from simply being pulled out of the manifold---it must be cut out/broken out
Buying a used manifold is not really great as the same leak will happen again over time. I cut the black fitting out and bough a 6061 aluminum bung that my welder welded onto the rear of the manifold. I can post it up as soon as I can find my pics and can relay to you the size I used.
If it helps, I can post pics of the black fitting after removed from the manifold as you will see that leaks here are not IF but WHEN.
If I were you, whatever you do, I would take the opportunity to remove the intake manifold and change all the vacuum lines as well as intake manifold gaskets. Makes it easier to deal with the seal and the vacuum lines are in hidden areas under the manifold.
Attached are the pics of my setup and pics of the original fitting. You Can see where I cut it out and how the original fitting works.
CNC machined 6061 aluminum Designed for 5/8" hose: FID-Turbo 5/8" Hose Barb Weld Fitting - Aluminum
Bought fitting off Amazon: Total length is 1 1/8". Diameter of the welding base is 15/16"
Thanks Mooks, great info. The strange part is that I didn't have a brake booster line going into this plug. I don't think DUDMD did either.
At any rate, a 22mm Samco silicone blanking cap and a little grinding on the tabs solved the problem until the engine or intake needs to come out. At that point a more permanent solution as above will be done.
On to the air intakes and a permanent near-ambient IAT solution (without water/meth)...
Thanks Mooks, great info. The strange part is that I didn't have a brake booster line going into this plug. I don't think DUDMD did either.
At any rate, a 22mm Samco silicone blanking cap and a little grinding on the tabs solved the problem until the engine or intake needs to come out. At that point a more permanent solution as above will be done.
On to the air intakes and a permanent near-ambient IAT solution (without water/meth)...
Something I realized (and maybe you can confirm) but don't the R230 platforms use SBC braking systems with the electronic braking system?. If so that would explain the lack of a brake booster line going to the rear of the manifold. On every other model, the rear fitting is a connection for the brake booster. If you do not have one, then I would just weld it shut.
08-15-2017, 10:55 PM
