Not AOS Failure

[Spockuk]

Hi

I have a problem with my Boxster S, which seems to be beating many 'specialists'. Can anybody here throw some new ideas into the ring ?

Boxster S, 2000, 75K. Originally, I had the usual problem of sudden blue smoke from the exhaust when driving hard, and then lifting off. The AOS was replaced, but the problem persisted, but not so severe, producing sudden puffs of blue smoke when lifting off from high revs (4500+). It was suggested that there could be oil pockets still which would burn off. After over 1000 miles, the problem persists as bad as ever. By blocking off the AOS to the throttle body, though, the problem goes away. As a long shot, perhaps the replacement AOS was faulty, so it's been replaced again. No joy. Compression has been checked and is OK, but all 6 spark plugs show some oil covering. Oil level is OK. AOS drain is OK. The sump was taken off, but nothing untoward could be seen. Nothing showing on the diagnostics. Pretty well everything external that could be checked has been. I'm now being told that further investigation requires engine out and strip for a 'fishing' trip with no guarantee of success. That almost makes it a write-off at today's prices.

I would really appreciate some other ideas / suggestions / tests we could work on.

[BYprodriver]

worn valve guides? In the UK contact Autofarm & Hartech.

[mattatk]

FAULTY AOS...sorry sort of relevant to this thread...

Has anyone experienced a faulty replacement AOS? Just curious, when I pulled the connector off the new AOS to throttle body (was trying to move AOS to make space to diagnose air leaks) it had a pool of oil in it??? New (less than 3 months) AOS shouldn't allow oil through to the intake??

Cheers,
Matt

[Spockuk]

Matt

I checked into this when my problems continued after fitting a replacement AOS. It is thought to be extremely unlikely that a 'new' AOS has failed. Most people I contacted hadn't heard of it ever happening. I suspect you've got a problem elsewhere, which is not dissimilar to mine.

[mattatk]

Yeh, I was thinking it was unlikely. My smoke is white & at start up for a few minutes.
I reckon there is too much air pressure differential pulling/pushing the oil straight through the AOS into the intake...

[Zeke]

The AOS is not too easy to replace. You might want to check the work and see if something isn't fitted right. I had to go at mine twice in one day.

[Wayne 962]

I'm guessing that the positive crankcase ventilation valve is plugged / clogged and causing higher than normal vacuum in the engine which may be drawing more oil than normal into the engine. Just a guess though, that's the only thing I can think of...

-Wayne

[mattatk]

What sort of diameter hole are you talking about Wayne? A couple of oil changes ago I had some plastic debris (reddish like tensioner ramps), wonder if the debris could've blocked it...
There isn't that much pressure on the oil cap though.

[mattatk]

Forgot to mention, my car being ROW 2001 S doesn't have the positive crankcase ventilation valve (or the secondary air pump for that matter). The 986 part catalogue shows M96.21 having a different air system with no valve?

[Harry Kamaltow]

There are AOS in the oil sump maybe one of them has gone bad somehow?
HK

[mattatk]

Was thinking about that. My next task is to get into the sump anyway.

[BYprodriver]

Originally Posted by Harry Kamaltow

There are AOS in the oil sump maybe one of them has gone bad somehow?
HK

This is highly unlikely & in any event will not have a impact on the OP's problem. The 2 AOS in the oil sump defoam oil returned to the sump from the heads by the scavenge pumps. The VOS (as Porsche labeled it) is mounted on the exterior right rear corner of the engine. The VOS depends on a internal diaphram to function properly & this diaphram eventually fails, YMMV.

[The Radium King]

i think wayne is correct - excess vacuum. it's the only way i can think of that you can get burning oil associated with a good aos. note that excess vacuum can kill an engine - it draws the oil mist away from the moving bits it should be lubricating, and can suck in seals as well.

uncertain what could cause it, but perhaps pull your sump first, before dropping your engine.

[Spockuk]

This is a resurrection of my first post, if I'm allowed ! I'm still having the smoke problem, but haven't been able to do much to it lately. However, I have had another look at the pipes to and from the AOS. The pipe from the AOS to the intake had oil in it, but the breather pipe from the crankcase into the AOS was dry. This is suggesting that oil is being sucked up from the engine via the drain tube. Has anybody heard of this happening elsewhere ?

[One986mi]

Can someone please say more about the Porsche "VOS" mentioned in this thread? I cannot seem to find this part for my 04 Boxster S. Does anyone have a part# of name for this part?

[Starter986]

Originally Posted by One986mi

Can someone please say more about the Porsche "VOS" mentioned in this thread? I cannot seem to find this part for my 04 Boxster S. Does anyone have a part# of name for this part?

Have you thought of phoning your local Porsche dealer?