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Spock
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Thanks for that. This seems a little overkill for a standard road car. Would my idea work: " What would happen if we blocked off the AOS entry to the throttle body, and fitted an oil breather after the AOS ? No oil vapour can get into the inlet, and the crankcase can breathe to atmosphere. Is there any liklihood of engine seal damage ? " But I'd still like to know what's causing it.
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The problem was, initially, a faulty AOS (I think). But the problem of smoke at high RPM after throttle closure has persisted after replacement. Another AOS unit has since been tried, but made no difference. " If you have it showing signs of smoke on over run then it points to a problem in the valve train with a worn guide/valve stem or damaged stem seal. " The problem started suddenly, so doesn't suggest wear. Also, the smoke is a large 'puff' and then stops. Wouldn't it continue smoking on over-run if it was worn components ? Blocking off the AOS stopped the problem. Is there a work-around? What would happen if we blocked off the AOS entry to the throttle body, and fitted an oil breather after the AOS ? No oil vapour can get into the inlet, and the crankcase can breathe to atmosphere. Is there any liklihood of engine seal damage ? I believe this sort of arrangement has been used on track cars.
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I don't have the numbers, but the guys were happy that they didn't indicate any problems. They've now checked the AOS drain, and think that isn't the problem, as it seems to be clear. They're now at a loss as to where to go. There doesn't seem to be any good reason to take the engine out and strip it down just on a 'fishing' trip. What else can cause AOS failure symptoms but not be due to a failed AOS ?
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We've disconnected the AOS breather into the throttle body, ran that into a container, and bunged the throttle body hole. There was no smoke, indicating no residual oil. As the symptoms are very similar to an AOS failure, it has been suggested that the drain channel for the AOS in the engine block could have become blocked. Revving the engine once or twice is OK, as the oil in the AOS would slowly drain away, but doing it repeatedly fills the AOS quicker than it can drain, and we get the smoke. Does this seem feasible ? Does anybody know if it's possible to clear the channel from 'outside' ie without taking the engine out ? Thanks all for your comments.
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If there was residue in the exhaust, it would surely burn off whenever the exhaust got hot, but I just get a 'lot' of smoke on gear change/lift off at 5000+ RPM. Below that, it runs normally. Also, there's no sign of oil deposits around the exhaust outlet.
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Thanks for the initial thoughts. It hardly loses any oil between changes (about 6000ml). Hasn't overheated, as far as I know - I've had the car just over 4 years. We have checked the oil level, and it's OK.
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Help !! I could use some direction with this .. Boxster S, 2000, 75K. Originally, I had the usual problem of blue smoke from the exhaust when driving hard, and then lifting off. The AOS was replaced, but the problem persisted. 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. 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, though. Oil level is OK. AOS drain is OK. 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. That almost makes it a write-off at today's prices. I would really appreciate some other ideas / suggestions / tests we could work on. Thanks.