CIS potential vacuum leak List

[Sunroof]

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

[gomezoneill]

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

[tirwin]

Injector o-rings and seals

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

Intake runners

[RDM]

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!

[boyt911sc]

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

[Paulporsche]

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.

[boyt911sc]

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.



Tony

[Sunroof]

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?

[1987 Porsche]

Here is a good post for testing:

Finding CIS vacuum leaks - the vacuum cleaner pressure test

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.

[1987 Porsche]

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



Lou