NJS_04_996

I'm in the process of attempting to replace the AOS in my 996 via the top side as described by Pelican Parts. Got all the way to the point of removing the left side air intake and realize there is a hose threading through the manifold which will prevent me from removing it. The hose runs from somewhere from the lower left side of the engine, through (under) the left intake, was cable tied to the underside of the rear plenum, then runs under the right air intake and finally snakes its way to the front where it terminates on the engine block (picture 2). My guess since it is just flexible plastic it is not carrying any fluids, but air? Naively I wondering if it could be cut and the securely reconnected, but I'll go mow my lawn and await your advice!

Ahsai

That's the AOS hose (to carry oil vapor) that connects the AOS to the bank2 engine case. I don't think you want to cut it. Just disconnect it from the AOS.

NJS_04_996

Thanks Ahsai- would that (hopefully!) be accessible from underneath then?
Presumably you have replaced one?

Ahsai

Yes it can be disconnected from the bottom of the car. Or from the top if you reach deep down with you left hand. The space is quite tight. You need to disconnect that anyway if you are replacing the AOS.

NJS_04_996

Looks like a bit of a catch-22 - can't see this tube at its connection to the AOS from underneath the car, and can't really get to it from the top with the intake manifold still there in my way. I think I feel it, although the tube I'm feeling feels more like delicate cardboard. I really don't think I have a choice - seems like if I make a nice straight cut in the center of the smooth, non corrugated section (just barely visible to the right of the circled area in picture 1) I can reconnect them with rubber sleeve. I guess I'll sleep on it......

Ahsai

No, please don't unless you plan to replace it. Any air leak there will wreak havoc to the a/f ratio and cause CEL.

rockhouse66

Might be helpful info for you in this thread;

https://rennlist.com/forums/996-foru...os-line-2.html

NJS_04_996

thanks Rock for the link- helps explain a lot. Tomorrow I will attempt to see if i can reach in from the left side and disconnect it from the AOS.

NJS_04_996

So I was successful in getting the intake manifold out of the engine bay this morning, and have clear view of the AOS. Yesterday I noticed two 1/2" (or so) rubber hoses that I didn't recall disconnecting in the first place, and now I can see that both of these hoses go to the top of the AOS unit. I have read elsewhere about coolant lines running to the AOS to prevent malfunctions in subfreezing weather. Presumably that is what these two lines are, and I certainly would have noticed leaking coolant if these somehow got pulled off without me knowing it. I don't know if the AOS had been replaced before (and it was a Florida car for its first 10 yrs), however I don't think it would have shipped from Germany with two loose hoses. Time to see if I can get the new AOS in.....

NJS_04_996

.....if I could only get the old AOS off that is - just can't get a socket on the left side bolt. About to give up and have it towed to the shop.

dan_189

There are many threads about AOS replacement it's quite involved and requires you to remove the left side intake and possibly lower the engine for more access.

How far have you gotten?

NJS_04_996

Dan, pretty much all the way there- I do have the left side intake off and the AOS backside bolt loosen. I can get my finger tips on the left side bolt, but because of nearby hoses, can't seem to align a socket to find the head of this bolt.

I'll check some of those AOS threads again- problem was I think the ones I had come across were the older style AOS units which connected sideways (horizontally) to the engine block. I have the newer one which bolts vertically into the block. Going to give it one more try this morning. Will try to see if I can place the socket on the bolt via my fingertips, then attempt to get the socket extension into it.

NJS_04_996

another "what is this tube" question

This is the chief offender in trying to get at the left side AOS bolt. It leads back up to the "Y" on the upper right, and does not have a hose clamp, so no fluid? Can it be removed?

dan_189

Dont quote me but that looks like a fuel line.

There was a thread about this exact access issue, have you lowered the engine slightly for more access? To be honest I haven't had to do this yet dreading the day I will have to though!

NJS_04_996

to be clearer, I'm referring to the rubber hose and not the metal one (I just realize the tip of the crude arrow is ambiguous )
But I think you're right....looking at a picture from another thread, it does seem to terminate on what could be the end of the fuel rail. Surprised its not clamped throughout.