CIS potential vacuum leak List
 

Looking to put together a vacuum leak checklist for my CIS. I know most of the usual suspects, but it would be helpful to get feedback for an area I might not consider on the CIS unit.

Thanks

Bob
73.5T/first CIS

Pop off valve where it's glued to the air cleaner housing.

Injector o-rings and seals

all old vacuum lines. I’ve replaced most of the rubber with silicone.

Intake runners

The airbox in places you can't see (underneath and / or in the back).

Incidentally, I saw the other night that plastic airbuses are available from Porsche for under $500 (gulp). Glad I had a spare that I could experiment on!

Vacuum leak.......
 

If you car has vacuum assisted brake booster, the braided hose from air box to metal tube before the tunnel and the curved rubber hose located near the booster.

Tony

There is an aluminum pipe that runs from the AAR and/or the AAV and passes next to the oil cooler on top of the engine block. A hole can rub through there, causing a vac leak. Mine was almost through when I discovered it while removing the airbox.

Crank case breather hose........
 

This picture was sent to me recently by ANDONI (Bob A.) while trying to investigate his cold start problem. The engine is a ‘74 CIS.

http://forums.pelicanparts.com/uploa...1586810080.jpg

Tony

Great suggestions...…………….
thank you.

Is their a smoke test for leaks? Take a big puff of a cigar and just blow it around watching for where it might enter? anyone ever try this?

Here is a good post for testing:

http://forums.pelicanparts.com/porsche-911-technical-forum/717648-finding-cis-vacuum-leaks-vacuum-cleaner-pressure-test.html

I use Tony's method: Take off the rubber boot on top, seal off the throttle body with a latex glove and also the two hoses that were connected to the rubber boot. After you have sealed the system, pressurize it with continuous supply of low pressurized air from a smoke generator or compressor. If just air from compressor spray the areas listed above with a soapy solution. Get the latex glove partially inflated during the test and observe for any source of air/smoke. Good places to inject the air are:
1.) Brake booster inlet to the airbox on drivers side of airbox.
2). POV.
3). Intake runner’s #1 or #4 injection port.

I did try the cigar method but did not have any success. That's why I built a smoke generator for a few bucks.

http://forums.pelicanparts.com/uploa...1586826009.jpg

Lou