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Old 06-07-2015, 02:47 AM   #1
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replaced aos still smoking, please help :-)

hi all,
i have just bought an 02 plate boxster 2.7l cheap because it smokes if not driven very gently.

went to porsche and bought a new aos

replaced yesterday also cleaned all intake, throttle body ect, theres was crud i dug out of the pipe that goes to pcv,

started car - no smoke, reved it up a few times still no smoke, assumed it was fixed, put it back together.

drove it 10 miles, gave it a bit of kicking and it was great no smoke, turned into my road 2nd gear and heard a hannibal lecture type noise for about 1 second then massive ammounts of smoke. :-(

car now smokes badly on startup, thinking it may be some residual i took it out and it cleared for a bit then came back.

if i undo the oil filler cap with car at idle the filler hose pops up under pressure, (is this normal?) but i can easily remove the cap.

if i cap off the intake pipe connection will it be safe to use and if the smoke stops is it maybe pcv stuck causing the issue?

i dont want to damage it, could it still be residual or can i test pcv at the aos pipe?

many thanks
barks
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Old 06-07-2015, 10:44 PM   #2
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mileage? do a dry and wet compression check to see if the engine is worn out. check for uniformity with the cylinders. if there is one which is lower than the others you may have trouble.
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Old 06-08-2015, 12:13 PM   #3
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thanks for reply,
tried to get compression test done yesterday but mate wasnt in,

put some wynns engine seal fixer in this morning which helps rejuvenate valve stem seals just in case.
got to work and checked the old aos, no rips tears or cracks? looked new,(blue diaphram), prob revious owner replaced and didnt fix issue?

so im thinking the new unit fixed the problem but only lasted 10 miles due to something odd?

got to engine after work, oil everywhere i had cleaned on saturday...

so i capped off the intake hole,

when stated car there is a very small amount of smoke coming from aos pipe, which increased when car revved. is this normal, crank breathing faster with revs?

drove home like i stole it, no smoke, interesting as i didnt clean anything this time so i could see if cleaning it on saturday was the reason it didnt smoke, obviously not, it must of been the new aos working for 10 miles.

the only conclusion at the mo is that the vacume is too great for the aos causing it to fail very quickly.

with it capped off the car drives superbly... enjoyed the drive home...

ive read the engine needs a small vacume to help with blow by , by sealing the rings but a small amount of blowby if there is any is better than chucking out massive amounts of smoke and risking hydro lock...

it going to stay capped all week for testing,

any opinions?

barks
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Old 06-08-2015, 04:19 PM   #4
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Not unusual for smoking to last for a while after AOS replacement and even intake cleaning as the CATs have to burn off the oil residue that has accumulated there when the AOS was letting oil into the intake and it was escaping unburned through the exhaust system. Lots depends on how long the AOS was bad and how bad.

Not saying the noise and your current situation is that.
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Old 06-09-2015, 05:26 AM   #5
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A couple of thoughts:

You didn't specify mileage - if 300K the engine is worn out.

Additionally, if the oil was neglected over a long period or if it sat for an extended period the rings may be sticking, this is common in other smoking cars so I'll assume it is in Boxsters. The trick I learned (and have successfully used) is 3 oil changes at 500 mile intervals. Skip cleaning additives as they destroy the lubrication properties of the oil, the quick oil changes work by refreshing the detergent in the oil which cleans the rings.
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Old 06-09-2015, 01:06 PM   #6
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thanks both,
ok, its done 120k miles with full porsche service history, last service was 1000 miles ago.

update,
so it drove home great yesterday with intake capped off, aos pipe open.

drove to work today its a 25 mile trip, drove great as i said im testing it to try and figure out whats going on, after around 20 mile i let it have it, it felt ok then a small amount of smoke, i thought it was residue as i was hitting it hard, backed off anyhow just in case, got to work and oil started dripping from engine...
the top was covered in the direction the aos pipe was pointing, anoying and a messy clean up but progress, its either not being sucked out by intake vacume and being pushed out or coming from somewhere else? which i doubt..

its lost about 1 litre of oil, however the digital display reads full but the dipstick reads empty!! yes trust the dipstick, but maybe someone put the wroing one in at some point?


so ive left intake capped off, and secured a pipe to the aos going to a plastic 2 litre bottle sealed at top but with holes around top section to breath, any oil will collect and i will know for sure its being pushed out.

anyone know the exact dipstick lenght, 02 plate 2.7l ?
is it possible engine removed at some point and the dipstick tube was cut then joined but now is longer?

so what could cause the oil to be pushed out past the aos?
is it possible the exhaust could be entering the crank case?
surely if it was it would just vent?
anyone got a link to the exact workings off the engine inc all aos pipes and pcv?

i also disconnected the pipe coming from the pcv and it wasnt that causing the slight smoking/ breathing.

its as if there is oil held in reserve somewhere and all of a sudden when the engine is hit hard it releases it pusing it upp the aos?

cheers
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Old 06-09-2015, 04:06 PM   #7
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Compression check done? I ask because of this theory:

Rev harder, more blowby, more pressure in the crankcase which must be relieved through the AOS which is designed to clean up a certain amount of oil mist but may be being overwhelmed or may have failed.

Also wouldn't be the first time someone got a bad AOS as a replacement.
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Old 06-10-2015, 02:48 PM   #8
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ok,
no oil in bottle,
oil covered engine again?
intake blocked and aos pipe into bottle.

1st checked exact amount of oil in car drained and measured. 7.6l without filter makes it 8.3l so digital guage correct, dipstic incorrect!

oil new so put back in at least for now.
compression test done, 11.5, 11.2, 10.5, 12, 13, 10 should be 11 so ok.

cleaned engine and all pipes again and put back together.

my theory at the mo is that the aos is working properly, however when the vacume is high it should shut to prevent oil being sucked into intake, this isnt happening so the only conclusion is there must be an air leak.. remember the hanibal lecture noise before it smoked,, on checking the aos to pcv pipe i noticed its not a tight fit, i think the seal has shrunk allowing air to be sucked in at high vacume.
ok how does that explain the oil on the engine, well as there was no vacume the rings wernt sealed so creating more crank pressure and pushing the oil past the aos to pcv seal?

so no smoke all way home as i drove it gently and tomorrow new seal and test it....

cheers
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Old 06-10-2015, 08:00 PM   #9
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Barks,
I wonder if someone else 'repaired' the vacuum hoses ? I ask because they are notorious for becoming brittle and cracking -even the oil filler pipe.
It is easy to mis-connect the rats nest of vacuum hoses.
Answering will take a lot of tedious poking around.
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Old 06-10-2015, 11:01 PM   #10
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ok, thanks,

i did check each one and clean all joints, yesterday i did hover around the oil filler flexible bend for a while but what i was feeling i think was the seam in the plastic.

of to work now update later

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Old 06-11-2015, 02:50 PM   #11
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found what i think to be the problem,

i went to fit a new o ring seal to the aos to pcv pipe at the aos end and i relised it should have the same fitting as the top pipe, push hard and it snaps on to form a tight seal.
the whole ring had been broken off previously and so when intake blanked off the oil would come out and when aos connected to intake the diaphram couldnt close at high vacume due to air being sucked in.
new pipe ordered and might as well replace pcv.

treated it to a new set of bosch coils and plugs today then washed it. :-)

cheers barks

Last edited by barks; 06-11-2015 at 02:53 PM.
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Old 06-13-2015, 02:13 AM   #12
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hi,
just a quick question,
ive just been on the phone to porsche to order the pipe and pcv,

they say it isnt a pcv its just a connection piece?
ive read that the pcv can stick open?

is it a pcv or a connection piece?, anyone know for definate?
its on the end of the long vent line that goes to the aos, connects onto the top o the cam cover passenger side.

cheers
barks
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Old 06-16-2015, 12:02 PM   #13
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ordered the connection piece, vent line and an oil filler seal.

since i cable tied the vent line on tight no smoke since, about 150 mile covered. think thats the issue.

however now have what feels like a missfire but isnt, statred new thread.

i dont normally talk to myself this much but it may help someone.. lol

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