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Multiple Vacuum Leaks and Fuel Pump Affecting Engine and Transmission

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Hi everybody, I have been following this forum for years, but never posted.  Its funny (in a painful way) to read these posts.  I guess it does make me feel better knowing others are having the same difficulty as myself.  I, like others, have been fighting vacuum leaks going on 1 1/2 years.  I have replaced the hose going to the booster, but the connection at the booster is crap.  It sent me on a goose-chase looking for vacuum leaks which I did find some, but the main one in still the booster.  Mine disguised itself by never throwing a code besides random misfire.  Then, add a fuel pump problem, a coolant leak (2nd pump genuine), and a slipping 4th gear (sometimes) to really understand my pain.  But I love the car.  That's why I can't let it go.  I must fix it and keep fixing it.  It's painful!  By the way I did use some gray Stuff IT gasket maker on the booster connection and she is starting to make a comeback again.  By comeback I mean its almost running without missing.  Almost:(  Still sucks to see my baby like this.  I know that it is a vacuum leak, but when I fix one I find another.  2004 Porsche Cayenne S 170000 miles.  I still have code for o2 sensor bank 1 sensor 1, random misfire, and cylinder 4 misfire that I'll be diving into tomorrow by changing the 02 sensor and switching the tower on 4.  The random misfire I believe is still a vacuum leak somewhere (or the **** booster still).  I need a smoke machine!  I saw several videos on youtube where they built one.  Here's what I've replaced so far in this car:  Rear driveshaft, front driveshaft, front differential, coolant tubes, fuel pumps, fuel filter, fuel regulator, rear hatch shocks, thermostat, water pump, front lower control arms, starter, manifold gaskets, spark plugs, plug towers, idler pully, engine stabilizer arm, radiator overflow, serpentine belt, all fluids many times, primary air pump, and brake booster vacuum line.  As you can see ownership of this car makes you own the car literally.  They wanted 8000$ to do the front differential, 3000$ for the coolant tubes, and $1300 for the starter at Porsche dealership, so that's when I started diving into the abyss I call fixing the cayenne fforrrreevverrrrr.  Six years later, I'm starting to believe I could rebuild the car, but I don't want to Knock Knock.  Peace brothas and happy driving (and fixing).  If any of you have advise on my problem I would love to hear from you!!!

Edited by coolbronco
added more parts to my parts list
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A few relatively easy things that I didn't see on your list: Have you replaced the valve cover gaskets? At this age they are almost certainly rock hard. Check for seeps around the gaskets. These can leak and cause stumble at idle and low loads. Another thing to check is the diaphragm valve for the crankcase vent. These diaphragms are notorious for tearing. It's located underneath a round black plastic cap on the driver's side of the engine towards the front of the vehicle, and is held on by a few tabs. You can inspect the diaphragm by removing this cap--carefully pry it off with a few screwdrivers. Look carefully, sometime the tears can be hard to see. The diaphragm is not available as a separate part from the dealer but there are aftermarket replacements.


Keep in mind that some O2 sensor fault codes can be caused by leaks in the intake system.

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Thanks for responding Brett968!  I was trying to get the cap for the crankcase vent yesterday, but I wasn't sure that the tabs were the only thing holding it on, so I wanted to wait to find out.   I'll do that right now.  The valve cover gaskets are definitely leaking.  When I pulled the spark plugs one was full of oil leaking from the internal valve cover gasket?  I am also worried that the intake is leaking too.  I'll order the valve cover gasket and the diaphram as a preventative measure.  Thanks!

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As far as I know, there are two aftermarket solutions for the diaphragm valve from separate manufacturers: a less expensive diaphragm-only solution from a Russian outfit, and a more complete solution that includes not only the diaphragm but the spring, cap, and internal plastic support. In my experience, the Russian-sourced diaphragm does not work properly as the geometry is not quite correct. I have not tried the other option yet--but it looks to be better from the images I've seen. (I repaired my original diaphragm with adhesive and it's holding for the time being.) You can find either of the above options on eBay from various sellers. The second solution is also available on Amazon: http://a.co/3fXpUra


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