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  1. #1
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    N54 "Boost Loss" Part throttle

    Okay. I've been chasing down this problem I've been having. Let's see if anyone can help.

    -Car has COBB w/ 93 octane ATR map, FBO with complete charge piping and upgraded DV's.
    -2,000 miles OEM turbos. Replaced all vac lines. 24,000 miles on the car. IJE0S. Alpina Flash.

    That's the mods that are relevant to my problem. Essentially, during part throttle, holding boost around 4psi or below with the throttle everything is spot on. Boost comes on hard with no delay. Once my throttle is pushed in enough to build boost more than around ~4psi, a loud air sound can be heard and my COBB tells me my boost is 1-2psi. This air sound and boost level will continue until I give it more gas (probably around ~60% throttle at this point), the sound will go away and boost comes up to where it should be (~12-14psi at ~60% throttle)

    My initial thought when I heard it was boost leak. Sounds just like one, but it isn't. My entire intake tract is perfect. Smoke tested up to 25psi no issues, rock solid. No codes ever thrown. My WOT logs WGDC is spot on. It's just this air noise and boost loss that occurs and I can't figure it out! My next thought was maybe my rear turbo inlet tube slipped off during the turbo install. I haven't visually checked this, but I don't see how this could cause my boost loss problem during a certain throttle input range, and then make no noise after around 60% throttle. No oil on the downpipes (If the tube came off I'd assume there would be from the check valve, no OCC)

    I'm confused at this point. WOT the car is strong, low throttle as well. My next thought is boost solenoids? Would this cause my problem by them going bad? At 24,000 miles?

    Thanks for the advice. I have logs if you want them from today, WOT.

  2. #2
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    Can you capture logs of what is going on while the problem is occurring, almost sounds like throttle plate is closing. Any codes? If you are hitting boost targets under WOT I don't see any chances of it being a boost leak.
    2011 E90 M3 \ Melbourne Rot Metallic

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    Click here to enlarge Originally Posted by lulz_m3 Click here to enlarge
    Can you capture logs of what is going on while the problem is occurring, almost sounds like throttle plate is closing. Any codes? If you are hitting boost targets under WOT I don't see any chances of it being a boost leak.
    I haven't yet. That's what I'm doing tomorrow morning. Boost leak is out of the question, it's got to be something else because the pressure test and WGDC are both fine. It's strange...Never throw boost codes. Let alone codes.

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    I'm having the same issue. Only at part throttle, low boost and leaky sound. Full throttle the car acts fine. I took it to bmw hoping they would replace my wastegates, but they don't feel anything is wrong with them. I changed solenoids, cleaned intake valves, put on a new charge pipe with tial bov, checked intercooler conections and my next step is to change vac lines.

  5. #5
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    Probably need to massage the torque request tables, really need logs to view guys.
    2011 E90 M3 \ Melbourne Rot Metallic

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    Click here to enlarge Originally Posted by lulz_m3 Click here to enlarge
    Probably need to massage the torque request tables, really need logs to view guys.
    If you want my WOT logs from today I'll gladly upload them, they just don't tell me much because I need to get the log of the event. Here's what my torque request table looks like. Table contents are stock throttle but I spaced the pedal position %'s a bit more as you can see from the highlight.

    Click here to enlarge

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    Sounds like could be the work of diverter valves. One post for day.

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    Click here to enlarge Originally Posted by Rob@RBTurbo Click here to enlarge
    Sounds like could be the work of diverter valves. One post for day.
    Rob,

    I originally thought this was the case too. It was happening on my stock diverter valves, so I swapped them out for the Forge ones (which I would have done anyways even without this issue.) No dice unfortunately. Same ordeal. DV vacuum lines were changed as well.

    By the way your PCV valve has been working great for me! Thanks

  9. #9
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    Could an issue with my vacuum canisters cause this?

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    Is there a way to test those besides just pulling the lines off and listening for released vacuum? Maybe switch them with someone else's, they are fairly easy to remove.

  11. #11
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    Bump

  12. #12
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    Logs man.... GET US SOME LOGSSSS!!!!
    2011 E90 M3 \ Melbourne Rot Metallic

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    Click here to enlarge Originally Posted by lulz_m3 Click here to enlarge
    Logs man.... GET US SOME LOGSSSS!!!!
    Lol. Going to get some now.

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    Click here to enlarge Originally Posted by lulz_m3 Click here to enlarge
    Logs man.... GET US SOME LOGSSSS!!!!
    Best one of the event.

    datalog1.zip

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    The only thing that is standing out to me is that you are overshooting your requested boost target at the beginning of the log, at times by 3-4 psi. Basically the DME wants 0 boost, but you are producing 3-4psi, I don't see where the throttle plate is compensating trying to close, but that could be an issue. You are not exceeding targeted load however, so its somewhat strange. @dzenno@PTF might see something i am not.
    2011 E90 M3 \ Melbourne Rot Metallic

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  16. #16
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    @Josh@Cobb, do you have any feedback?
    2011 E90 M3 \ Melbourne Rot Metallic

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    I'll try to take a look tomorrow. I've been slammed this week. Sorry guys. @E90Company can you email me any logs you have? It's easier for me to remember what I need to check out if its in my inbox.

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  18. #18
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    @Josh@Cobb Sure thing, just sent you two logs.

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    2 out of 2 members liked this post. Yes Reputation No
    @E90Company

    I have the EXACT same thing happening on my car but running a different tune (procede). I think lulz_m3 is on the right track. Turbos are spooling up at light throttle, and since the throttle plate is mostly closed, it builds some pressure in the charge pipe (which is read by the MAP sensor, ~3 to 4 psi although requested boost is at 0).

    As you keep opening up the throttle (but still boost target = 0), there is less restriction at the throttle body, and the slight spool from the turbos no longer creates pressure in the charge pipe.

    And continuing to increase throttle now causes the DME to "request" boost, which causes the wastegates to spool the turbos enough to create pressure although the throttle plate is becoming more and more open.

    Hope that makes sense as I typed it. One thing: if you can try to move your default wastegate position to as open as possible, this may reduce or eliminate this effect.

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    Click here to enlarge Originally Posted by MAC335 Click here to enlarge
    @E90Company

    I have the EXACT same thing happening on my car but running a different tune (procede). I think lulz_m3 is on the right track. Turbos are spooling up at light throttle, and since the throttle plate is mostly closed, it builds some pressure in the charge pipe (which is read by the MAP sensor, ~3 to 4 psi although requested boost is at 0).

    As you keep opening up the throttle (but still boost target = 0), there is less restriction at the throttle body, and the slight spool from the turbos no longer creates pressure in the charge pipe.

    And continuing to increase throttle now causes the DME to "request" boost, which causes the wastegates to spool the turbos enough to create pressure although the throttle plate is becoming more and more open.

    Hope that makes sense as I typed it. One thing: if you can try to move your default wastegate position to as open as possible, this may reduce or eliminate this effect.
    Thanks for the comment! It definitely makes sense. If I can give what you advised me a shot, I will do so. I'm not sure how to make that happen in ATR though. Hopefully Josh could fill me in; see what he says about it.

  21. #21
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    Normal. At partial throttle there isn't enough physical load to keep the turbos spooled. Every turbo car I've every owned and/or driven does the same thing.

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    I think MAC335 is on the right track.

    The diverter valves will crack open when there is about a 3-4 psi differential between charge pipe pressure and post throttle plate manifold.

    That is probably the hissing sound you are hearing because at part throttle, the throttle plate will be creating a restriction that forces unequal pressure on both sides of it if the turbos are spooling.

    The diverters pick up on the pressure diferential caused by the closed throttle plate and start to bleed off boost.

    Once you start to open up the throttle, pressure equalizes and the diverters close and you are back to boosting.

  23. #23
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    Click here to enlarge Originally Posted by DCAFS Click here to enlarge
    I think MAC335 is on the right track.

    The diverter valves will crack open when there is about a 3-4 psi differential between charge pipe pressure and post throttle plate manifold.

    That is probably the hissing sound you are hearing because at part throttle, the throttle plate will be creating a restriction that forces unequal pressure on both sides of it if the turbos are spooling.

    The diverters pick up on the pressure diferential caused by the closed throttle plate and start to bleed off boost.

    Once you start to open up the throttle, pressure equalizes and the diverters close and you are back to boosting.
    Starting to think the same. @lulz_m3, you experience this?

  24. #24
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    No, but i also have a Tial BOV, so it wouldn't display the same characteristics as the diverter valves.
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    Makes sense.

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