P0172 code, vacuum fitting... (850 GLT)

RexSpeed · Post by **RexSpeed** » 05 Jan 2011, 20:10

So after having reached in under the manifold a handful of times looking for the common vacuum leak that causes the P0172 code, I finally found the leak. I have about 3" of vacuum line attached to the nipple on the manifold and since the fitting was tight and I could feel any further along those 3" I figured that wasn't the cause. It was.

Feeling a bit ambitious tonight I squeezed my hand in even further and discovered that those 3" of vacuum line all that's connected to that nipple. The end of the line was just wide open. I plugged it off just to get rid of the leak, but now I'm wondering where the other end of that line is supposed to go.

What is that manifold nipple supposed to supply a vacuum/boost signal to?

Klausc · Post by **Klausc** » 05 Jan 2011, 22:11

Need a little more info. Where is the nipple and the 3" of vacuum line? Right side, left, front? There are a lot of lines around the engine.

RexSpeed · Post by **RexSpeed** » 06 Jan 2011, 19:47

Klausc wrote:Need a little more info. Where is the nipple and the 3" of vacuum line? Right side, left, front? There are a lot of lines around the engine.

Far left and underside of manifold, right next to the t-stat housing.

Post by **jblackburn** » 06 Jan 2011, 20:06

That goes back to the vacuum supply port at the intake hose of the turbocharger.

It attaches just behind the fat pipe on the PTC nipple. You can run a length of vacuum tubing from there up and over the top of the engine back to the nipple to it.

Check at the same time to see if your PCV system is clogged once you get the line connected (see the write-up pinned at the top of the 850 forum for the tell-tale video of white smoke out the dipstick tube at idle).

RexSpeed · Post by **RexSpeed** » 10 Jan 2011, 15:38

jablackburn wrote:That goes back to the vacuum supply port at the intake hose of the turbocharger.

It attaches just behind the fat pipe on the PTC nipple. You can run a length of vacuum tubing from there up and over the top of the engine back to the nipple to it.

Check at the same time to see if your PCV system is clogged once you get the line connected (see the write-up pinned at the top of the 850 forum for the tell-tale video of white smoke out the dipstick tube at idle).

I'll go ahead and get the line attached as you recommend, but I'm a little confused by it. What function is served by having a hose connected to two vacuum sources with nothing in between? Functionally, does it matter if the two points are connected or just plugged individually?

The PVC system was done about 14 months ago. Once the weather here warms up a bit I'll pull the PTC stuff to make sure it's not gunked up again, but I cleaned it all out when I did the rest of the PCV.

Post by **jblackburn** » 10 Jan 2011, 17:29

It provides a vacuum source from the intake manifold at idle, when it can help the PTC nipple suck up oil vapors that blow past the turbo seals back into the oil separator box. Under throttle, the intake manifold is under positive pressure from the turbocharger, so the vacuum hose serves no purpose then as the engine's crankcase pulls the vapors through on its own.

One reason to keep it connected is just to keep the car from throwing check engine lights at you.

RexSpeed · Post by **RexSpeed** » 10 Jan 2011, 20:39

Okay, more confusion...

Vacuum line #1 (see pics) doesn't attach anywhere. The other end is loose with a plug in the end. What is this line supposed to connect to? What is the canister thing (by-pass valve?)

If I understand your previous post correctly, line #3 is supposed to connect to the back of the manifold (by the steering pump). However, on my car it's connected to this t-fitting (#2). There is a check-valve in line between the turbo inlet and the t-fitting as well. Is this correct, or do I have some lines swapped around?

Post by **jblackburn** » 10 Jan 2011, 21:13

Line #3 is where it is supposed to be. The one above that, with the small elbow into the valve with the bigger hose coming out of it kinks up and goes over to the other side of the intake manifold.

That silver canister is the SAS (secondary air injection system) valve. The fat hose there attaches to an air pump under the battery tray, and the vacuum line from that valve goes up towards a valve on the radiator shroud.

See this small yellow line at the top of this picture into the intake manifold? The vacuum line for the SAS attaches into the other end of the valve that one's connected to. That small purple line that snakes past the transmission dipstick is the one on my car that goes up there.