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Watch those vacuum leaks! This is a cross post from another thread I chimed in on, but figure this is worth sharing straight up as it was a PITA finding the PNs for some of these hoses. Note these parts are for a 08-10 CS, other models may differ, but the same principles stand.
The whole family has weighed in from driving and consider it a big improvement in performance from what seemed like a small leak. In fact, the wife has been driving it on and off the last week and says she like the V8 sound when it winds out and feels more peppy Even my son is like yeah that thing moves! (I don't want to know more than that)
I feel like a moron for not doing this sooner as I knew the AOS drain was "patched" from the PO.
Symptoms: - Slight lull in performance when downshifting under load (like up a hill). - The dreaded 30-40 upshift lag and shudder between 3rd and 4th. - Inability to hold RPM smoothly in manual shift mode. Impossible to stay smooth above 3000 RPM with light throttle. (WOT masked the issue) - No CELs appeared due to the vacuum leak.
The part broken/cracked was the AOS drain line into the head/block that comes out from under the drivers side valve cover breather. While I was in there I also did the following to have a clean sheet: - Porsche Throttle Body Gasket 94811014402 https://www.eeuroparts.com/Parts/180...t-94811014402/ - Take out and clean TB while you are there. I used Berrymans TB cleaner with success. (Brake cleaner probably would have been fine as well) - Porsche Vent Line 94810724702 = AOS to Intake Manifold (mine broke in half when I touched it, so I suspect a leak there as well) https://www.eeuroparts.com/Parts/194...e-94810724702/ - Porsche Engine Crankcase Breather Hose 94810724502 = rear crossover breather https://www.eeuroparts.com/Parts/404...e-94810724502/ - Breather Vent Hose from bottom of Oil Separator - 948-105-245-04-OEM = lower drain from AOS to head/block (was cracked and the major cause for the vacuum leak. POs shop tried to repair with a fuel hose bridge - nope.) https://www.pelicanparts.com/More_In...105-245-04-OEM - AOS diaphram (was not needed, but replaced it anyway)
Now the CS feels like a 14 second car again! The light throttle response is wonderful and pulling through slow turns is effortless w/o the transmission hunting for gears. Holds revs in manual mode smoothly! Just a beast the way it should be... Feels mint and I am pleased!
Thanks for putting all this in one place for future reference! I had some pipes replaced when the manifold came off for access to the thermostat... and the pipes glued into the thermostat housing spun in the housing because of glue failure... so coolant pipes AND vacuum pipes are problems. I didn't experience any performance issues from the vacuum leaks, but the engine did seem to run a bit more smoothly once everything was replaced.
CEL came on a week after we purchased it and yep, vacuum leak. I've looked but haven't found anything obvious. I'll take a closer look at that AOS hose. Are there any other common vacuum leaks I can check for? I haven't procured a vacuum pump yet, but I feel that's where I'm headed. Thanks for the info @Pillow.
Every plastic vacuum or hot water pipe under the hood is subject to turning brittle over time/heat cycles. Additionally, composite parts with metal pipes (or plastic pipes) glued into them are subject to having the GLUE fail, leading to leaks that can be minor or major. Aside from that, rubber hose is also subject to breakdown over time from heat cycles. The safest course of action is to replace all the rubber and plastic items under the hood when the vehicle is old enough for brittleness in plastic, failure of glue, or cracking of rubber to begin being an issue.
Plastic parts include engine coolant hoses or at least their old o-rings that have gotten flat and lost their resilience.
Don't forget to check the carbon canister area. I discovered my pressure valve slightly cracked open and still need to replace it - $ 250 - but that might be sucking air into the hose taking the vapors to the engine.
Dilberto, can you please comment on where you introduced the smoke, and did you do so with high pressure?
I bought a smoke tester of amazon to try and track down what I believe might be a vacuum leak somwhere. I started at the hard pipes going into the AOS. Capping off one end adding smoke into the other.
I did start to see leaks near the front intercooler pipes / air filter area, as your video shows, but then realized it was coming out the air box since I didnt cap those off, both sides (drain hole in airbox or maybe even passing throught the filter and coming out the airbox intake acordian tube, so I dont think thats abnormal to see it there. Once I removed the pipe from the mass to the air box, then I got a clean read, and no leaks.
However, this smoke tester is not high pressure, so I am wonder if some leaks only appear under boost.
At least the PCV system doesnt seem to be leaking, but I do still have oil around the breather pipe from the AOS headed down to the turbo. No smoke came from it, so not sure what to think, other than I am testing wrong with this smoke machine.
Last edited by Corvetteboy6988; 08-03-2023 at 06:10 PM.
Dilberto, can you please comment on where you introduced the smoke, and did you do so with high pressure?
I bought a smoke tester of amazon to try and track down what I believe might be a vacuum leak somwhere. I started at the hard pipes going into the AOS. Capping off one end adding smoke into the other.
I did start to see leaks near the front intercooler pipes / air filter area, as your video shows, but then realized it was coming out the air box since I didnt cap those off, both sides (drain hole in airbox or maybe even passing throught the filter and coming out the airbox intake acordian tube, so I dont think thats abnormal to see it there. Once I removed the pipe from the mass to the air box, then I got a clean read, and no leaks.
However, this smoke tester is not high pressure, so I am wonder if some leaks only appear under boost.
At least the PCV system doesnt seem to be leaking, but I do still have oil around the breather pipe from the AOS headed down to the turbo. No smoke came from it, so not sure what to think, other than I am testing wrong with this smoke machine.
12-19-2019 | 02:11 PM
Fix those vacuum leaks!
Even my son is like yeah that thing moves! (I don't want to know more than that)
