Vacuum Line Troubleshoot

[Ricks911s]

Okay. Think I've narrowed down my rough engine running problem. I posted earlier in the engine rebuilding forum (see the old thread here) . . . but probably was better suited here.

Here's the run down
(1) 1981 911 engine in a 1976 body
(2) Connected all fuel lines, oil lines, electrical lines, and vacuum lines
(3) 1976 carbon canister has 3 inputs and 1981 has 2 inputs
(4) I think I'm mixing up the vacuum/carbon canister lines (specifically the line that feeds into the airbox)

Here's the line that goes from the rear side of the carbon canister to the air box:



Next, on the drivers/front side of the carbon canister goes to this line on the 1981 engine. So here's the path of the line , carbon canister -> connecting to line on 1981 engine -> fed into a T-line -> which fed to the drivers/left side of the airbox

Pictures to Illustrate:

Here's where line from carbon canister connects to 1981 engine



And here it connects to the drivers/left side of the airbox. Note that while not visible in this image, this is a T-line (that is, after it comes out of the airbox it splits, with one line being the one I showed above).



I believe now that this last line (the line from the carbon canister that hooks up to the line on the 1981 line that feeds into a line that goes into the airbox) is improperly connected. Here's the question(s), as a result:

(1) Because I think this second line is hooked up improperly to the carbon canister, (ie, maybe it should hook up to something else), where does this line go to on a stock '81?

[Ricks911s]

This line, which is grouped together and runs to the back of the airbox doesn't have any line to hook into on the chassis side?

Thoughts?

[T77911S]

the big hose in the first goes to the vac assist for the brakes on my car.
if you suspect any of this as being the problem, unplug the hose and plug the port on the airbox to see if it runs better.
JW did a post about that hose cracking and causing air leaks, if you have the vac assist, the line runs to the front of the car. i pulled a vac on my line to test it for leaks, it is very hard to get to.
sure sounded like a WUR issue as posted in the previous post.

do a search for MCA, he posted a LOT of CIS pics, may be of some help, although that line will not be connected since his motor was out of the car.
did you wire in the computer?
the pics are unclear to me as to where things go.

[patrick300]

i have a 77 with a 2.7 and i too am trying to figure out where the lines go for the carbon canister there are 2 lines coming off the canister going to the left side of the engine and one coming from the front of the car, one of the hoses go too the fan housing, ones goes too the airbox and the other goes to the air box right below the throttle body but i am not sure if i have them on right anyone know which one goes where?

[dlagerstrom]

First, the 'vacuum' lines for the canister are NOT part of the true 'vacuum' on the CIS. It took me a while to figure this out. Yes, there is a vacuum pulled on the canister from the airbox, but if you have a leak, it does not have any effect on the metered air. The only canister connection to the airbox should be on the nipple that is just outside of the pop-off valve area. Note that it is inside the air filter but not yet beyond the flapper. This means that if you don't have it hooked up, it will not effect your idle etc.

The other 2 lines you mention are for parts that I suspect are not on your car and should be plugged. The 'T' connector, as stated by T77911S, is for the brake booster on an '81. If you don't have it, it will cause a major air leak and rough idle. I suspect the smaller line from the back of the throttle body is the small line that goes to the cruise control. If you don't have cruise, this should also be blocked off as it will also effect metered air.

Hope this helps. Good luck.

[Ricks911s]

This is just what I needed to know. Thanks.

We'll see how much of an improvement this makes. I'll update you guys after I make the adjustments.