I've been having a recurring boost issue with my TT. It drives smoothly, and you wouldn't know anything is wrong until you dip into boost. It maxes out, every time at .4 bar which I understand is limp mode.

I say it is recurring, because I let it sit for a week and when I finally drove it, all was normal. Pulled great, full boost and held strong. About 2 weeks later, I'm at .4 bar again.

To figure it out I've done the following:

-Checked wastegates for smooth actuation, lubed with WD-40. Seemed OK.
-Pulled off the exhaust and inspected cats, was looking for a honeycomb element to be loose and plugging the flow. Checked out OK.
-Removed and inspected DV's, F hose, Y pipe below DV's, metal Y pipe connections, N75 conenctions. No issues found.
-Plugged in Durametric, N75 seemed to operate OK. Did some logged runs, PDF attached.

Next I am going to put together a boost leak tester to see if I can find anything. I bet I have a leak somewhere. But in the meantime, would somebody who knows what to look for check out my Durametric log? It is attached here in PDF format. I did a few WOT pulls through the rev band.

Noteworthy: My car has an EPL K16 tune, fabspeed maxflow, and 200cell cats.

Thanks,
Connor

 

What did Tony say???

 

Hmm he'd prob be a good person to talk to... Good idea. Just sent him an email.

 

Thanks a lot Tony!

-Connor

 

Well, there you go! Let us know what you find!

 

I got to boost leak testing yesterday, turns out I've got a pretty big leak (I think, read last paragraph please)

What I did was plug the turbo outlet hoses on both sides, and used a schreider valve to pump it up. I've got a pressure gauge on it as well. I couldn't even get it to 4psi. I heard a leak coming from around the throttle body area, or at least central to the engine bay.

So I pulled off the metal Y-pipe last night, and my plan is to go back to Home Depot and make another plug for the Y-pipe to throttle body hose. I figure I can start to isolate the leak, if its not leaking there I know it is somewhere before the throttle body.

Does this procedure sound about right? One thing I am a bit confused about though... intake/exhaust valves overlap breifly as the cylinder goes from exhaust stroke to intake stroke. So if any of the 6 cylinders is in that position of overlap, won't you have all the air you are puming in for the boost leak test go out straight through the open exhaust valve? Then you'll be chasing your tail trying to find a false boost leak. Would appreciate insight on this.

Thanks,
Connor

 

Well I found out that one of my DV's wouldn't hold boost after about 8psi. I have supposed "upgraded" Bailey Motorsports DV's as well. I tried several times to fix it by opening it up, cleaning, and relubing the piston. It still never held more than 10psi reliably. So I ordered a kit from Forge (I hear parts are interchangable) that includes a choice of stiffer springs and spacers to try and get it functioning correctly. As a backup, I also ordered some Bosch 710N DV's as replacements. FWIW, the other Bailey DV held 20+psi just fine.

I hope this is the whole source of my boost leak. We'll see after I install the new parts.

 

Stick with the Bosch 710N , they are reliable and don't need all the adjustments unless you are running mad boost and HP other wise the forged stuff in more PIA than they are worth. I have a set of Titan Motorsport (made by Forge as it came in the Forge box) just sitting there collecting dust and I am running in the 580 awhp on bosch DV without a problem

 

Yea, thats what I figured. Everyone wants the shiny billet ones, but you're just giving up reliability.

 

If you are only seeing .4 bar boost most likely the boost control solenoid is shot.
Start with the easy stuff. The wastegates on the factory turbos only have .4 bar springs in them. When the solenoid failes it will failsafe to .4 bar
The part number for the solenoid is. 996.605.155.00
Wouldn't be the first one I've see fail.

 

As to the suggestion above, I ordered a new N75 valve. Also ordered the O-ring seal between the T-body and intake manifold, and the 2 check valves. Should all come in a few days.

After the install of my 710N DV's, my boost leak is still there. Did another boost pressure test, still have a big leak somewhere. It wont even get up to 4psi with my big craftsman air compressor. The DV's were just one problem.
I think the leak is coming from somewhere behind the throttle body. The are a bunch of hoses coming off the intake manifold...is that check valve that everyone speaks of back there? With my lowly 4psi, I sprayed a bunch of soapy water all over the place and didn't spot any leaks. This weekend I think I'm going to lower the engine a few inches so I can see further back there.
I also checked the operation of my wastegates, with a mityvac hand pump. They were synchronised at least. Both just started to move between 5 and 6psi. Does that sound right?
-Connor

 

Is the rubber connection sleeve tight or fully engaged between the y pipe and throttle body. Mine poped off tonight at the drag strip.

 

Yep, that's nice and tight. I've sprayed a lot of soapy water all around and haven't spotted the leak. I believe it is the check valve that stems from the intake manifold. Haven't dug into it yet though.

 

So, another update is due. My issue was indeed the check valve, that comes off the top of the plastic intake distributor right after the throttle body. Yesterday I dug into it, new checkvalve in hand for replacement. Well, damn that sucker was stuck on there. Stuck on so good, that I broke off the plastic barb connecting to the plastic intake distributor. I was pulling as straight as I could, in tension, and still broke it before the valve came off. Pain in the a**!
Well, that's one way to get the valve off. Once I had it removed, I blew through it (the way that its supposed to not allow flow) and it was clearly the culprit. Now I have on order a new plastic intake distributor and it should be in next week. I just want to drive this damn thing... Anyway, pic attached:


BTW - experimenting with the check valve, I managed to get it to hold pressure occationally by blowing/sucking at different pressures. This makes total sense now, why I could have full boost one time and a huge boost leak next time.

 

Mine was totally blown, so was my buddies.

Be very careful when removing, the piece on top of the plenum will snap very, very, easily.