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Discussion Starter #1
Hi,

I'm new to this forum.
I am having limp mode problems with my ALH TDI.I have replaced VNT actuator and vacuum lines. I wanted to rule boost leak out before replacing n75 or MAF and am trying to do a boost leak and have read 1000q boost leak post but am not doing it correctly. I have corked hose to breather (black puck on valve cover), removed oil cap, and baggied and clamped intake hose after air cleaner box. When I apply 10psi to hose just downstream of check valve after n18 valve I hear air bubbling in the crankcase so no pressure is held. Where exactly do I introduce air?


Thanks for any help.

Pottermark
 

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Any line that leads to the intake system. I believe that when you're applying air to that line you are putting it to the vacuum pump. One place you can add air is the crank case vent breather heater. It's a small port on the accordion hose which heats it to prevent it blocking in the winter. You can also use the main intake hose if you have an adapter.
 

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Thanks ChittyChitty,

Thanks for the reply also the maintenance articles on the site are a great help.

I made and adapter (A yogurt container with a hole drilled through the bottom) that sealed well at the intake accordion pipe and at the nipple where I was introducing air into it. I don't hear any leaks at any hoses but some hissing/leaking air coming into the crankcase when I put my ear near the oil filler. Shouldn't the system seal and hold the 10psi?.
 

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There is some leakage around the piston rings but it should more or less hold pressure. If the camshaft is in the right position the valves are open and it could let air pass by. Remove any blockages in the air system so that they aren't sucked in and crank the engine a split second to move the engine. Or just remove the TB cover and rotate the camshaft sprocket a little manually. If it holds no pressure whatsoever you have a big boost leak somewhere or a hose is loose. If it holds a little pressure but bleeds down, you have a regular sized leak somewhere.
 
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