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    Boost rise then fall

    Quick one guys…

    Whilst I'm building the other engine I'm getting the current car to Stage 0 and I'm having a bit of an odd problem. Current engine idle is fine runs fine doesn't smoke doesn't hesitate, however when I accelerate Either full throttle or mildly the boost will build to wherever it decides to sit depending on acceleration severity nice and quickly but will then drop slightly back and maintain that level. For example if I put my foot down, by about 3000 rpm the boost has built to around about 0.6 bar but will then drop back by about 0.1 bar and stay comfortably at that level through the Rev range. Wastegate is set to open around 4 psi and I have tried fiddling with this pressure a little to see if it makes any difference

    Anyone got any ideas what this is? I put a differently tuned ECU in and it quite happily boosted to around one bar so the wastegate despite being stock seems able to hold itself closed so I'm not sure why the Boost seems to be cut back at stock. If I can I'll get a video and put a YouTube link to it as I don't think I'm explaining it very well!

    Thanks all!
    Si

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    Oh forgot to mention it is a 1996 850 T5 running completely stock and returning on average mpg of about 26 to 28 on a roads and inner city driving

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    Quote Originally Posted by Bigsi15 View Post
    Quick one guys…

    Whilst I'm building the other engine I'm getting the current car to Stage 0 and I'm having a bit of an odd problem. Current engine idle is fine runs fine doesn't smoke doesn't hesitate, however when I accelerate Either full throttle or mildly the boost will build to wherever it decides to sit depending on acceleration severity nice and quickly but will then drop slightly back and maintain that level. For example if I put my foot down, by about 3000 rpm the boost has built to around about 0.6 bar but will then drop back by about 0.1 bar and stay comfortably at that level through the Rev range. Wastegate is set to open around 4 psi and I have tried fiddling with this pressure a little to see if it makes any difference

    Anyone got any ideas what this is? I put a differently tuned ECU in and it quite happily boosted to around one bar so the wastegate despite being stock seems able to hold itself closed so I'm not sure why the Boost seems to be cut back at stock. If I can I'll get a video and put a YouTube link to it as I don't think I'm explaining it very well!

    Thanks all!
    Si
    With the standard ECU that sounds normal to me. That's similar to what mine was before I changed the ECU.
    It would go to about just over 8Psi and drop to just under 8psi and sit there.

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    I agree. Thought boost would always be higher when initial acceleration due to compressor spooling up. Once it reaches max spool for the given throttle request, it will naturally fall away slightly.
    Due to the 16T having practically no lag, the boost is very controllable using your right foot.

    However, 0.1bar is only 1.4psi so you must have a boost leak somewhere or something is very wrong!

    Have you tried unplugging the boost pressure solenoid and seeing what boost you get? Boost will be controlled by the wastegate and this is set by manufacturer at around 3-4psi. You should see 3-4psi on your gauge with the BPS disconnected. If not, you have a leak somewhere.
    Last edited by LeeT5; Wednesday 16th March 2016 at 11:34.
    2014 V60 Polestar 6spd Auto :: Polestar map peak boost 17.4psi :: IPD 3" DP + 150cel :: Polestar 2.5" exhaust :: Paddle Shift Geartronic :: Black glass :: Maxton Splitter :: K+N Filter :: IPD Aluminium Top engine mount :: Brembo 6 pots :: 20" Polestar rims :: Brembo 371mm floating discs :: Sensus RTi + DAB + BT + WIFi :: D3S XENARC 6000k Active bending headlights

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    I've just had a thought!

    The one way valve is probably failing. Is there oil misting around your oil filler cap or oil sitting around the head?
    It's next to the throttle body on the manifold, there's 2 pipes. The upper pipe goes to this one-way valve.

    Mine just failed and it did exactly what you describe. Boost would build to 10psi, then drop to 6psi and sit at 6psi. blocked that pipe temporary and boost sits and stays at 10psi

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    Quote Originally Posted by Mart5in View Post
    I've just had a thought!

    The one way valve is probably failing. Is there oil misting around your oil filler cap or oil sitting around the head?
    It's next to the throttle body on the manifold, there's 2 pipes. The upper pipe goes to this one-way valve.

    Mine just failed and it did exactly what you describe. Boost would build to 10psi, then drop to 6psi and sit at 6psi. blocked that pipe temporary and boost sits and stays at 10psi
    There are TWO one way valves and he's only getting 1.4psi not 6 or 10 or anything above 2!!!

    Martin is right though. Replace both the one way valves first and then see how she goes. You'll probably only gain about 2 psi if they leak. Otherwise, your gonna need a smoke leak test.
    2014 V60 Polestar 6spd Auto :: Polestar map peak boost 17.4psi :: IPD 3" DP + 150cel :: Polestar 2.5" exhaust :: Paddle Shift Geartronic :: Black glass :: Maxton Splitter :: K+N Filter :: IPD Aluminium Top engine mount :: Brembo 6 pots :: 20" Polestar rims :: Brembo 371mm floating discs :: Sensus RTi + DAB + BT + WIFi :: D3S XENARC 6000k Active bending headlights

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    Thanks guys I'll definitely have to look into that as I wasn't aware of any one way valves. . Leet5 luckily it's not quite as bad as you mention it is only dropping by about 0.1 not down to 0.1 LOL! Mart5in this sounds quite plausible are you talking about the vacuum hoses or is there something else in there I missing? I've never noticed the valves other than the idle control valve?

    Thanks for all your help guys

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    Quote Originally Posted by Bigsi15 View Post
    Thanks guys I'll definitely have to look into that as I wasn't aware of any one way valves. . Leet5 luckily it's not quite as bad as you mention it is only dropping by about 0.1 not down to 0.1 LOL! Mart5in this sounds quite plausible are you talking about the vacuum hoses or is there something else in there I missing? I've never noticed the valves other than the idle control valve?

    Thanks for all your help guys
    Clearly, I misunderstood your original post then? Anyway, here are the valves so you can easily find them and replace them.
    Mr Tim Williams will concur....they are very often overlooked and never replaced.

    Vacuum valve No1

    Name:  IMG_2401_zps55176b63.jpg
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    Vacuum valve No2

    Name:  IMG_2402_zpsd167cb26.jpg
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Size:  82.6 KB

    Name:  PCVreplacement13_zps707bab52.jpg
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    Last edited by LeeT5; Saturday 19th March 2016 at 15:00.
    2014 V60 Polestar 6spd Auto :: Polestar map peak boost 17.4psi :: IPD 3" DP + 150cel :: Polestar 2.5" exhaust :: Paddle Shift Geartronic :: Black glass :: Maxton Splitter :: K+N Filter :: IPD Aluminium Top engine mount :: Brembo 6 pots :: 20" Polestar rims :: Brembo 371mm floating discs :: Sensus RTi + DAB + BT + WIFi :: D3S XENARC 6000k Active bending headlights

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    That's no problem I probably didn't word it very clearly thanks for the pictures I know exactly what your on about now brilliant. Il give those a go and see if it helps!

    Thanks again

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    Mine arrived today in the expensive Volvo packaged bags.

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    Markyb if yours were also for an 850 t5 would you mind posting the part number and price? Thanks buddy

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    Mine were for a p2 R

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    Wonder if there is much/any difference?

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    So are both these present and in the same places on a Ph2 T5? Would they be recommended to be swapped out as part of Stage 0 maintenance?
    2001 V70 T5 (Manual) - The Turnip
    1999 9-5 Aero (Manual) - Sven

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    Quote Originally Posted by Gold 'N' Brown View Post
    So are both these present and in the same places on a Ph2 T5? Would they be recommended to be swapped out as part of Stage 0 maintenance?
    Yes.
    2014 V60 Polestar 6spd Auto :: Polestar map peak boost 17.4psi :: IPD 3" DP + 150cel :: Polestar 2.5" exhaust :: Paddle Shift Geartronic :: Black glass :: Maxton Splitter :: K+N Filter :: IPD Aluminium Top engine mount :: Brembo 6 pots :: 20" Polestar rims :: Brembo 371mm floating discs :: Sensus RTi + DAB + BT + WIFi :: D3S XENARC 6000k Active bending headlights

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    .......
    Last edited by 960kg; Sunday 20th March 2016 at 13:10.


    Mercedes C320CDI Sport Estate 3 litre V6 7 Gear Auto
    Remap 290bhp 628Nm torque @ 1600revs 45.1mpg

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    Quote Originally Posted by 960kg View Post
    .......
    960KG, why have you changed your post or deleted it? I noted what you said and your wrong!
    Have you realised your mistake or has admin edited your reply?
    2014 V60 Polestar 6spd Auto :: Polestar map peak boost 17.4psi :: IPD 3" DP + 150cel :: Polestar 2.5" exhaust :: Paddle Shift Geartronic :: Black glass :: Maxton Splitter :: K+N Filter :: IPD Aluminium Top engine mount :: Brembo 6 pots :: 20" Polestar rims :: Brembo 371mm floating discs :: Sensus RTi + DAB + BT + WIFi :: D3S XENARC 6000k Active bending headlights

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    The valves shown in the pic are in different places on the 850 I think, those are ME7 pics?

    Valves on my 850 were attached to the radiator fan shroud

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    Quote Originally Posted by Mart5in View Post
    The valves shown in the pic are in different places on the 850 I think, those are ME7 pics?

    Valves on my 850 were attached to the radiator fan shroud
    Yes, they are P2 R pictures. Exactly the same on a P2 T5.

    I can't remember if they are in the same location on a P1, but I really posted the pictures so that the OP understood which valves I was referring to.
    2014 V60 Polestar 6spd Auto :: Polestar map peak boost 17.4psi :: IPD 3" DP + 150cel :: Polestar 2.5" exhaust :: Paddle Shift Geartronic :: Black glass :: Maxton Splitter :: K+N Filter :: IPD Aluminium Top engine mount :: Brembo 6 pots :: 20" Polestar rims :: Brembo 371mm floating discs :: Sensus RTi + DAB + BT + WIFi :: D3S XENARC 6000k Active bending headlights

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    Quote Originally Posted by LeeT5 View Post
    960KG, why have you changed your post or deleted it? I noted what you said and your wrong!
    Have you realised your mistake or has admin edited your reply?
    I deleted it myself as i then noticed that the hose the valve was on went onto your inlet manifold which was removed.

    Not a very clear indication, however congratulations for reading it as that is why it was there....lol


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