So I replaced my Air/Oil separator
10-12-2010, 02:12 AM
#1
Racer
Thread Starter
So I replaced my Air/Oil separator
Last week, I noticed that my 112,000 mile 996 was starting to idle a little erratically - not too bad, but definitely not normal either. Then the Check Engine light came on, and stayed on. I went to a friend's shop and they plugged in a code reader. While I can't remember the code, the end result was that the system had detected a big vacuum leak; in fact, we could actually hear it sucking air. I was told it was likely the AOS. I went home, researched it a bit, and found that a good test for that was try to pull off the oil cap while the engine was idling (normally it comes off easily). As predicted, it was sucked on there tight - so tight, I could barely get it off.
So, it seems I had a AOS failure.
After some consideration, I decided to tackle this myself, but there's so little real DIY info out there. It's piecemeal, at best. I put together a basic plan, figured I'd take my time, and ask questions when needed. In fact, I'm lucky enough to have a friend who lives down the street who happens to be a Porsche dealership mechanic - and he's really good. He offered to answer any questions I might have and come on by to take a look and offer advice. Perfect.
The back of the car was put on jack stands and the left rear wheel removed, in case I'd need to gain access (in fact, this helped me to retrieve the sockets dropped down onto the case all too regularly
). The air filter box was removed and put aside. The tasks ahead were to remove the throttle body, disconnect some electrical connections and hoses, remove the left side intake manifold bolts, then remove the intake plenum and varioram plenum, and finally pull out the intake manifold. Only then would I have access to the AOS.
More to come...
So, it seems I had a AOS failure.
After some consideration, I decided to tackle this myself, but there's so little real DIY info out there. It's piecemeal, at best. I put together a basic plan, figured I'd take my time, and ask questions when needed. In fact, I'm lucky enough to have a friend who lives down the street who happens to be a Porsche dealership mechanic - and he's really good. He offered to answer any questions I might have and come on by to take a look and offer advice. Perfect.
The back of the car was put on jack stands and the left rear wheel removed, in case I'd need to gain access (in fact, this helped me to retrieve the sockets dropped down onto the case all too regularly
). The air filter box was removed and put aside. The tasks ahead were to remove the throttle body, disconnect some electrical connections and hoses, remove the left side intake manifold bolts, then remove the intake plenum and varioram plenum, and finally pull out the intake manifold. Only then would I have access to the AOS.More to come...
Last edited by 450knotOffice; 10-13-2010 at 02:58 AM.
10-12-2010, 02:46 AM
#3
Racer
Thread Starter
So, first I removed the throttle body. I unplugged the electrical connection up on the upper left corner. It's a bit of a bugger (as they all are), but just squeeze the top and bottom of the connector while pulling gently and it should pop out. move the connector aside and then remove the four 10mm bolts that attach the throttle body to the plenum. Pull it out and store it away in a clean place. I'll re-post the shot above to make it clear, along with another one.
In the second shot, you'll see a couple of hoses that come together into a union at the upper left corner of the intake plenum. The clip that attaches them to the plenum is a mystery to me, but I fiddled with it, twisting and squeezing while I pulled and it finally popped off. I never figured out how it worked, but it was off, so I didn't investigate further.
That big hose on the left of the picture that ends in a pointed contraption needs to be unbolted where you see that bracket just behind and above the alternator in that shot. Unbolt it and move it aside.
In the last picture, you can see that I lowered the engine as far as it would go before hitting the suspension sub-frame (before I did all of the disconnecting of hoses and electrical lines I just described). The timing of the engine lowering is probably not too important - other than you want to have it down BEFORE you try to remove the intake manifold bolts. I can't imagine trying to do that with the engine tucked up high in the engine bay. You can see that it adds about three inches at least to the working space above the engine.
To lower the engine, place your floor jack and a large block of wood under the engine and support it. Then climb under the car and look for the two engine mount nuts just behind the rear bumper. Remove them. You'll need an 18mm deep socket for that. Now, lower the engine carefully with the floor jack until the engine is just about on top of the suspension cross member - and leave it there for the duration. I placed a couple of jack stands and wood under the oil pan in case the floor jack deflated over time. It didn't.
In the second shot, you'll see a couple of hoses that come together into a union at the upper left corner of the intake plenum. The clip that attaches them to the plenum is a mystery to me, but I fiddled with it, twisting and squeezing while I pulled and it finally popped off. I never figured out how it worked, but it was off, so I didn't investigate further.
That big hose on the left of the picture that ends in a pointed contraption needs to be unbolted where you see that bracket just behind and above the alternator in that shot. Unbolt it and move it aside.
In the last picture, you can see that I lowered the engine as far as it would go before hitting the suspension sub-frame (before I did all of the disconnecting of hoses and electrical lines I just described). The timing of the engine lowering is probably not too important - other than you want to have it down BEFORE you try to remove the intake manifold bolts. I can't imagine trying to do that with the engine tucked up high in the engine bay. You can see that it adds about three inches at least to the working space above the engine.
To lower the engine, place your floor jack and a large block of wood under the engine and support it. Then climb under the car and look for the two engine mount nuts just behind the rear bumper. Remove them. You'll need an 18mm deep socket for that. Now, lower the engine carefully with the floor jack until the engine is just about on top of the suspension cross member - and leave it there for the duration. I placed a couple of jack stands and wood under the oil pan in case the floor jack deflated over time. It didn't.
Last edited by 450knotOffice; 10-13-2010 at 03:03 AM.
10-12-2010, 03:37 AM
#4
Racer
Thread Starter
Now that the engine has been lowered and the throttle body is off and some basic connections are disconnected, it's time to dig in deeper.
The first task should be to loosen all eight of the big hose clamps connecting the plenums to the intake manifolds. I used a 7mm socket with extension to make quick work of that job. Now leave it. Don't try to remove the plenums yet, you will likely just waste a lot of time trying.
Next, loosen and remove ALL of the intake manifold bolts. Trust me on this (I learned through trial and error throughout this job) - if you remove the manifold bolts first, you'll then be able to move the manifold outboard a bit to enable easy removal of the the two plenums.
The hardest job yet is finally upon you, your poor arms, and your patience. Trying to get the 10mm intake manifold bolts off is not easy - especially the last one in the very front (my favorite expression always began with an F. My neighbors probably think I'm crazy now - muttering to myself while hugging the engine of my beloved 996
). The bolts aren't tight; they're just hard to get to. Actually, the rear five aren't too bad. It's the previously mentioned last one. Number six. Here's what I finally figured out: Do NOT try to come at it at any angle with a swivel socket. It won't happen. If you use a 1/4" drive socket extension about the height of the manifold itself - maybe 7 or 8 inches, and leave the wrench off for the time being, you can come around the left side with your left arm and then, as you feel your way past the edge of the manifold, come straight down - STRAIGHT DOWN - and feel for the bolt head down there. If you've gotten your socket near to where it needs to be, it should slip right onto the bolt head with only a little wiggling to find it. I HIGHLY recommend that you go in bare handed at first - with no wrench. Try to "learn" the layout of the manifold down there with your fingers, Find the bolt head. Feel where it is in relation to other landmarks. Get familiar with it. Then, when you're comfortable finding it every time with your left hand (basically you index finger only), try it with the socket and extension. You should be able to find the bolt head if you come absolutely straight down on it. It's a tight fit in there, but don't give up. Once you're on it, bring the wrench in, carefully attach it to the extension and slowly loosen the bolt.
Make sure you have a magnetic pickup stick. You WILL drop sockets and bolts onto the case.
Now you can see the AOS at the front left. As my Porsche mechanic friend recommended to me, don't pull any water hoses off of it just yet. Pull off the big hose on the right (with that funny connector again) and that's all.
Now, head down underneath the car with a light and get into position to see the AOS from below. You'll see the bellows and it's clamps. My Porsche mechanic friend told me to just take some pliers, squeeze the clamp, and pull it (the clamp) up and off the metal tube that the bellows attaches to. It's a bit ungainly and will deform the hell out of the rubber bellows, but no worries - you have a new one. Now, take your trusty 10mm 1/4" drive socket and about 15 inches of extensions and come in from the side and remove the two bolts that hold the AOS onto the case. Get a screwdriver or something similar and start wedging it outboard. Once it's clear of the case, climb back topside, grab the AOS and pull it up and back toward the rear. Once you have it in front of you, it's a simple matter to pull off the two water hoses, but be aware that you will spill a few ounces of coolant, so have a small container ready for the overflow.
Woohoo!! The AOS is out!
The first task should be to loosen all eight of the big hose clamps connecting the plenums to the intake manifolds. I used a 7mm socket with extension to make quick work of that job. Now leave it. Don't try to remove the plenums yet, you will likely just waste a lot of time trying.
Next, loosen and remove ALL of the intake manifold bolts. Trust me on this (I learned through trial and error throughout this job) - if you remove the manifold bolts first, you'll then be able to move the manifold outboard a bit to enable easy removal of the the two plenums.
The hardest job yet is finally upon you, your poor arms, and your patience. Trying to get the 10mm intake manifold bolts off is not easy - especially the last one in the very front (my favorite expression always began with an F. My neighbors probably think I'm crazy now - muttering to myself while hugging the engine of my beloved 996
). The bolts aren't tight; they're just hard to get to. Actually, the rear five aren't too bad. It's the previously mentioned last one. Number six. Here's what I finally figured out: Do NOT try to come at it at any angle with a swivel socket. It won't happen. If you use a 1/4" drive socket extension about the height of the manifold itself - maybe 7 or 8 inches, and leave the wrench off for the time being, you can come around the left side with your left arm and then, as you feel your way past the edge of the manifold, come straight down - STRAIGHT DOWN - and feel for the bolt head down there. If you've gotten your socket near to where it needs to be, it should slip right onto the bolt head with only a little wiggling to find it. I HIGHLY recommend that you go in bare handed at first - with no wrench. Try to "learn" the layout of the manifold down there with your fingers, Find the bolt head. Feel where it is in relation to other landmarks. Get familiar with it. Then, when you're comfortable finding it every time with your left hand (basically you index finger only), try it with the socket and extension. You should be able to find the bolt head if you come absolutely straight down on it. It's a tight fit in there, but don't give up. Once you're on it, bring the wrench in, carefully attach it to the extension and slowly loosen the bolt.Make sure you have a magnetic pickup stick. You WILL drop sockets and bolts onto the case.
Now you can see the AOS at the front left. As my Porsche mechanic friend recommended to me, don't pull any water hoses off of it just yet. Pull off the big hose on the right (with that funny connector again) and that's all.
Now, head down underneath the car with a light and get into position to see the AOS from below. You'll see the bellows and it's clamps. My Porsche mechanic friend told me to just take some pliers, squeeze the clamp, and pull it (the clamp) up and off the metal tube that the bellows attaches to. It's a bit ungainly and will deform the hell out of the rubber bellows, but no worries - you have a new one. Now, take your trusty 10mm 1/4" drive socket and about 15 inches of extensions and come in from the side and remove the two bolts that hold the AOS onto the case. Get a screwdriver or something similar and start wedging it outboard. Once it's clear of the case, climb back topside, grab the AOS and pull it up and back toward the rear. Once you have it in front of you, it's a simple matter to pull off the two water hoses, but be aware that you will spill a few ounces of coolant, so have a small container ready for the overflow.
Woohoo!! The AOS is out!
Last edited by 450knotOffice; 10-13-2010 at 03:21 AM.
10-12-2010, 04:14 AM
#5
Racer
Thread Starter
Now, that it's out, the installation is straightforward. It REALLY IS the reverse of removal.
Find some good grease and lube up the O-ring that goes into the case. Climb back under the car, and slide it back into place. Do NOT be dismayed to see a gap between the case and the AOS when fully tight. That's how the mounting system seems to be designed. It does not sit flush. As for the bellows and it's lower clamp, I did what most here do - and my Porsche mechanic said is common - and didn't end up using the factory clamp. I tried, but it was a pain. Instead, I went with a simple hose clamp - works great. But first, I pushed the AOS in as close as I could, came in with the bolts, and drew them down carefully until the AOS was secured tightly. Then I came back to the bellows, made sure it was positioned properly onto it's down-tube, and then installed the hose clamp. Done. Climb back to the topside and re-install the two water hoses and the other larger hose.
The easiest re-assembly (and I tried every incorrect method - trust me) involves slipping the intake manifold back into place first - but leave five of the the six bolts out. The sixth bolt, that blasted one in front, really can only be installed by putting it into its hole in the intake manifold first - BEFORE you slip the manifold into position. If you're worried about it falling out, then tape it loosely to the manifold first. Trust me - you WILL NOT get the bolt into the hole with the manifold already in place. I tried...and tried. Once the manifold is in place with the one forward most bolt sitting in place but not engaged - and all of the other five bolts NOT YET installed - reposition the intake plenums and their associated rubber sleeves back onto the right and left intake manifolds (noting their positions when they initially came out, by the way). Leave the hose clamps loose for now. Do not tighten them up yet. Now, position the left intake manifold back over its mounting holes and re-install those five remaining bolts. Tighten them down, but not too tight (the manifold is plastic).
After you've tightened the intake manifold bolts, go back to the hose clamps holding the plenums in place and tighten them down, making sure that the two plenums are oriented the same way they were when you removed them.
Now, raise the engine back up onto its engine mounts, re-install the engine mount lower nuts and tighten.
Re-install the throttle body and plug its electrical connection back in.
Re-attach the hoses and electrical connections you removed earlier. Re-install the air filter box, re-attach the wheel. Finally, lower the car to the ground. Start it and look for any leaks. You should be good to go.
Find some good grease and lube up the O-ring that goes into the case. Climb back under the car, and slide it back into place. Do NOT be dismayed to see a gap between the case and the AOS when fully tight. That's how the mounting system seems to be designed. It does not sit flush. As for the bellows and it's lower clamp, I did what most here do - and my Porsche mechanic said is common - and didn't end up using the factory clamp. I tried, but it was a pain. Instead, I went with a simple hose clamp - works great. But first, I pushed the AOS in as close as I could, came in with the bolts, and drew them down carefully until the AOS was secured tightly. Then I came back to the bellows, made sure it was positioned properly onto it's down-tube, and then installed the hose clamp. Done. Climb back to the topside and re-install the two water hoses and the other larger hose.
The easiest re-assembly (and I tried every incorrect method - trust me) involves slipping the intake manifold back into place first - but leave five of the the six bolts out. The sixth bolt, that blasted one in front, really can only be installed by putting it into its hole in the intake manifold first - BEFORE you slip the manifold into position. If you're worried about it falling out, then tape it loosely to the manifold first. Trust me - you WILL NOT get the bolt into the hole with the manifold already in place. I tried...and tried. Once the manifold is in place with the one forward most bolt sitting in place but not engaged - and all of the other five bolts NOT YET installed - reposition the intake plenums and their associated rubber sleeves back onto the right and left intake manifolds (noting their positions when they initially came out, by the way). Leave the hose clamps loose for now. Do not tighten them up yet. Now, position the left intake manifold back over its mounting holes and re-install those five remaining bolts. Tighten them down, but not too tight (the manifold is plastic).
After you've tightened the intake manifold bolts, go back to the hose clamps holding the plenums in place and tighten them down, making sure that the two plenums are oriented the same way they were when you removed them.
Now, raise the engine back up onto its engine mounts, re-install the engine mount lower nuts and tighten.
Re-install the throttle body and plug its electrical connection back in.
Re-attach the hoses and electrical connections you removed earlier. Re-install the air filter box, re-attach the wheel. Finally, lower the car to the ground. Start it and look for any leaks. You should be good to go.
Last edited by 450knotOffice; 10-13-2010 at 03:28 AM.
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10-12-2010, 02:20 PM
#10
very nice DIY, much appreciated considering a lot of people had to replace this part.
Can you describe how much force is now required to lift the oil cap with a brand new AOS ?
Can you describe how much force is now required to lift the oil cap with a brand new AOS ?
10-12-2010, 07:06 PM
#12
Racer
Thread Starter
As for time...
I took my time, and was learning as I went, so it took me just a tad over two casual days. However, now that I've done it, I think it would take me about 7 hours total.
I took my time, and was learning as I went, so it took me just a tad over two casual days. However, now that I've done it, I think it would take me about 7 hours total.
