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Hot!Smoke from the exhaust on boost

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dlknight
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Re: Smoke from the exhaust on boost 2020/05/22 23:19:48 (permalink)
Oh yes the fun and games removing the turbo
Been there done that and will probably be in there again as I should have replaced the catalytic convertor with a bypass at the same time and sent my turbo off for inspection and repair...

Current
1990 Panther Black 944 Turbo
2000 Violet Blue 911 Carrera 2
Gone
1987 Alpine White 944S with ProMAX Performance Chip
'88 Black 944 2.5, '96 Pug 306 XSI, '72 VW Type 2 Dormobile
marojojoem
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Re: Smoke from the exhaust on boost 2020/05/23 15:53:48 (permalink)
Sorry for the saga here but on investigating the inlet ducting and hoses, there is quite a bit of oil accumulating around the intercooler inlet and outlet so unless I'm missing something obvious the turbo requires a rebuild. From what I can see the rotor and bearings are fine but I guess the seals have gone. Here's hoping its not too much of a mission to remove.

1986 944 Turbo
2004 Alfa 156 Sportwagon
1985 944 Lux (sold)
PSH
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Re: Smoke from the exhaust on boost 2020/05/23 16:03:39 (permalink)
When you say 'bearings seem ok'?...there should be no play whatsoever. I remember thinking mine felt ok until re-checking it after rebuild....:)

944 Turbo......was 368BHP/382Torque.... now more...
PhilKent
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Re: Smoke from the exhaust on boost 2020/05/23 16:59:17 (permalink)
Fair amount of oil in the inlet can be from 2 sources, Air/Oil separator breather pipe which feeds back into the inlet. Or Turbo. I had similar issues several years ago and checked the compressor wheel for play, felt nice and 'tight' i.e. no play,but spun freely. However when I removed the turbo the turbine side had loads of lateral play in the bearing.
You can check the AOS by disconnecting the breather pipe from the intake, use a blanking cap, and run the pipe into an old coke bottle or similar strategically placed somewhere in the engine bay while you go for a 'spirited' drive. i.e build up the revs and boost. Oil build up in the bottle will almost certainly suggest crankcase pressure from ring blow by.
I ended up replacing the turbo and rebuilding the engine! Hope you're not in that territory as it's not cheap, but I enjoyed the experience.

PhilKent
marojojoem
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Re: Smoke from the exhaust on boost 2020/05/23 17:05:57 (permalink)
Absolutely no radial or axial play that I can detect and nice free rotation but I guess the bearings are routinely replaced in any overhaul 

1986 944 Turbo
2004 Alfa 156 Sportwagon
1985 944 Lux (sold)
marojojoem
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Re: Smoke from the exhaust on boost 2020/05/23 17:13:43 (permalink)
Phil thanks for the advice on the AOS. So leaving the turbo aside, is the problem likely to be high crankcase pressure or can the AOS fail and cause oil in the inlet in which case I suppose its a cheap fix to replace or overhaul

1986 944 Turbo
2004 Alfa 156 Sportwagon
1985 944 Lux (sold)
PhilKent
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Re: Smoke from the exhaust on boost 2020/05/23 18:07:17 (permalink)
Not sure how the AOS can fail as it's just a baffle tube with vent pipe (as far as I know, I've not opened one up), but I thought mine was leaking so replaced it last winter. It's a pig of a job, requires v.small hands to get the bottom bolt out! It may be worth removing it to give it a clean out, but unlikely to 'fail' unless it cracks and leaks oil everywhere. Alternative as has been suggested is to fit a separate AOS and run the engine AOS outlet to this (lots of folk do this mod, as have I). It's more of a performance mod than a solution to crankcase pressure issues. If you have a std car and want to keep it that way, I wouldn't do it.

PhilKent
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Re: Smoke from the exhaust on boost 2020/05/23 19:10:44 (permalink)
I could be wrong but I seem to recall that the AOS has some form of coarse filter which can block with dirty oil/carbon  build up and thus result in increased crank pressure. It's been a while so can't swear to this as fact
 
Pete

944 Turbo......was 368BHP/382Torque.... now more...
dlknight
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Re: Smoke from the exhaust on boost 2020/05/23 20:41:12 (permalink)
Nope the AOS is completely empty and just a void - worth checking the rubber hoses though that come off the AOS mine had split right underneath the intake manifold.
 
 

Current
1990 Panther Black 944 Turbo
2000 Violet Blue 911 Carrera 2
Gone
1987 Alpine White 944S with ProMAX Performance Chip
'88 Black 944 2.5, '96 Pug 306 XSI, '72 VW Type 2 Dormobile
944Turbo
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Re: Smoke from the exhaust on boost 2020/05/25 20:32:36 (permalink)
marojojoem
Sorry for the saga here but on investigating the inlet ducting and hoses, there is quite a bit of oil accumulating around the intercooler inlet and outlet so unless I'm missing something obvious the turbo requires a rebuild. From what I can see the rotor and bearings are fine but I guess the seals have gone. Here's hoping its not too much of a mission to remove.


If they haven't been apart for a long time there usually is - might be worth cleaning them out and checking again after a 1000 miles or so,
Tony

944T Coupe - personalised ;) but needing work
944T Cab - Standard
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