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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N57 / M57 Turbo Diesel Discussions - 335d > Installed mechanical boost guage. Boost is uneven?



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      05-01-2016, 10:20 AM   #1
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Installed mechanical boost guage. Boost is uneven?

I am trying to troubleshoot an intermittent hesitation. The only thing I know now is that boost fluctuates 5psi up and down when the hesitation is occurring. The hesitation is so fast that the data logging apps are not useful. To help collect info I have installed a mechanical boost gauge with a T off my boost sensor. See video below of boost gauge in action. This is what I get accelerating gently on the highway.

So far I have changed all vacuum hoses, actuators, boost sensor (twice), red charge hose and seals on charge hose on intake side. It is an 09 E70 35d w/ 45k miles. Thanks

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      05-01-2016, 11:07 AM   #2
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When you mentioned boost sensor.. What sensor are you referring to? Aftermarket sensor for the boost signal?
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      05-01-2016, 11:18 AM   #3
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Can't see speed or rpm in the video. And the video moves around alot. Can you fill in the blanks, so we can understand what the issue is? The boost gauge will move as you drive.
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      05-01-2016, 12:18 PM   #4
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Quote:
Originally Posted by 335dlci View Post
When you mentioned boost sensor.. What sensor are you referring to? Aftermarket sensor for the boost signal?
The OEM boost sensor in the intake now has a T in the hole to allow both the OEM and mechanical hose.
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      05-01-2016, 12:22 PM   #5
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Quote:
Originally Posted by DWR View Post
Can't see speed or rpm in the video. And the video moves around alot. Can you fill in the blanks, so we can understand what the issue is? The boost gauge will move as you drive.
I am accelerating gently and the boost is jumping around. It should be even and is even when the issue is not happening. In the video I am in 6th accelerating from 55 to 65. The boost should go to 20ish and stay there. Also, the needle on the gauge should not be vibrating as mush as it is. I will try to get a better video later today. thanks
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      05-01-2016, 03:52 PM   #6
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What you're seeing is the result of electronic wastegate control.
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      05-01-2016, 03:57 PM   #7
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^ 1+
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      05-01-2016, 08:28 PM   #8
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Shove a qtip worth of cotton in the boost gauge hose to stop the vibration of the needle, if that doesn't work you can install a small cheap inline fuel filter
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      05-01-2016, 09:02 PM   #9
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Quote:
Originally Posted by UberArchetype View Post
What you're seeing is the result of electronic wastegate control.
+2, Its PWM, I've seen this on n55 and even on a s63.
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      05-02-2016, 08:08 AM   #10
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Here is a better video that shows the bigger 5 psi jumping around. Still think it is PWM? This was with a small even attempt to accelerate. I will try the cotton trick that probably will get rid of the needle small 1psi vibrating. Thanks

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      05-02-2016, 11:12 AM   #11
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Boost pressure is subject to instantaneous fluctuation on engine demand, unlike things such as fuel or oil pressure. Snubbing it will only reduce the accuracy and timing of the reading.
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      05-02-2016, 12:13 PM   #12
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Quote:
Originally Posted by UberArchetype View Post
Boost pressure is subject to instantaneous fluctuation on engine demand, unlike things such as fuel or oil pressure. Snubbing it will only reduce the accuracy and timing of the reading.
Agreed, but the fluctuating is intermittent. Most of the time the boost is not bouncing around like that. When the boost bounces around, the power disappears and it does not run well.
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      05-02-2016, 02:27 PM   #13
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Quote:
Originally Posted by Bob@BPC View Post
+2, Its PWM, I've seen this on n55 and even on a s63.
Dont those both have a blow off valve type bypass which would allow the boost to be released very quickly from the charge side? 335d doesnt have any mechanism in the intake for releasing that pressure so it would have to rely entirely on the turbo speed increasing and decreasing. It would surprise me that the turbo can speed up and slow down fast enough to replicate those boost spikes, especially the slow down part.
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      05-02-2016, 03:21 PM   #14
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Quote:
Originally Posted by Hoooper View Post
Dont those both have a blow off valve type bypass which would allow the boost to be released very quickly from the charge side? 335d doesnt have any mechanism in the intake for releasing that pressure so it would have to rely entirely on the turbo speed increasing and decreasing. It would surprise me that the turbo can speed up and slow down fast enough to replicate those boost spikes, especially the slow down part.
The N20, N55, & S55 have a "diverter valve(s)" that bypasses the air just in front of the compressor wheel and pushes air out the filter, and the N63/S63/TU engines are just like the m57, no bypass at all.
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      05-02-2016, 03:43 PM   #15
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Quote:
Originally Posted by Bob@BPC View Post
The N20, N55, & S55 have a "diverter valve(s)" that bypasses the air just in front of the compressor wheel and pushes air out the filter, and the N63/S63/TU engines are just like the m57, no bypass at all.
Interesting. Seems like a bit of a crazy idea, how do they regulate boost spikes from closing the throttle? Or does the computer just not allow the throttle to snap shut if boost is high?
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      05-02-2016, 04:19 PM   #16
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Here is a much better video. The X5 is actually surging forward each time the boost goes back up. One other symptom I forgot to mention is highway MPG. I get 21 on the highway but can get 22 around town. Something is not right and lack of codes has me guessing. thanks

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      05-02-2016, 08:00 PM   #17
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Is your engine stock?
Perhaps the EGR rates are erratic - try to disable both HP and LP and see if the problem changes.
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      05-03-2016, 06:11 AM   #18
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Originally Posted by ingenieur View Post
Is your engine stock?
Perhaps the EGR rates are erratic - try to disable both HP and LP and see if the problem changes.
Yes it is stock. I can try disconnecting the EGRs. I can disable the LP by removing the vacuum hose. For the HP one is it best to just disconnect the electrical connector? It seems to have less power when I do that. I am also going to check out the diverter valve is that is the only thing I have not looked at yet. thanks
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      05-04-2016, 08:09 AM   #19
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Quote:
Originally Posted by smassey321 View Post
Most of the time the boost is not bouncing around like that.
Most of the time the electronics are not stepping all over themselves commanding stupid WG variations.

"Most" of the time.
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      05-04-2016, 12:28 PM   #20
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Quote:
Originally Posted by smassey321 View Post
Here is a much better video. The X5 is actually surging forward each time the boost goes back up. One other symptom I forgot to mention is highway MPG. I get 21 on the highway but can get 22 around town. Something is not right and lack of codes has me guessing. thanks
Much better video, thanks. Hooper is right, no way the turbos can be responding that fast. That is some quick valve actuation. Throttle valve, bypass valve, that kind of thing.
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      05-04-2016, 01:46 PM   #21
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Quote:
Originally Posted by DWR View Post
Much better video, thanks. Hooper is right, no way the turbos can be responding that fast. That is some quick valve actuation. Throttle valve, bypass valve, that kind of thing.
Agreed. Can Rheingold cycle the throttle or bypass so I can visually inspect? I unplugged the throttle for my drive home from work and it did not hesitate a single time so this is progress. I am now unsure if the throttle is bad or just reacting badly to some other sensor input. Others have had oil get in the throttle to damage the electronics so I probably will take it apart next.

Last edited by smass; 05-04-2016 at 05:23 PM..
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      05-05-2016, 05:38 PM   #22
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Just did another quick test. Disconnecting the air mass meter and leaving the throttle connected also makes the issue go away completely. More power and less jerking around. I can't wait for it to run this way all the time. I have a feeling disconnecting these disables the EGRs and I should check those out next.

I tested the throttle with Rheingold and it passed. The engine did stall when the test started the first time and I am unsure if that is normal. It barely kept running for the second test.



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