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Default Sudden low boost, no boost leak, O2 sensor codes - 07-13-2017, 09:25 PM

Basics:
N54, 115K miles

This morning was able to hit 22 PSI as normal and car was performing fine. After leaving work this evening, it drove fine for a few minutes but then I noticed a loud whining/ moaning sound like a boost leak when the car would try to build boost, and could not make over 3 PSI or so.

I have a known fouled O2 sensor i know I need to replace but been putting off for a couple months. I've been having intermittent O2 sensor faults (2C7B lambda probe behind *** con 2, signal ; 29E0 fuel mixture control ; 29E1 fuel mixture control 2) but that has not caused any low boost or other issues except I will sometimes get a Safety 5 from the bad O2 signal variance.
Edit: new precat o2 sensors installed, see below.

When I first experienced the low boost this evening, i got new O2 sensor codes ( 2C9D Lambda probe heating in front of *** con 2, signal ; 2CA7 Lambda probe heating in front of *** con 2, function ; 2CAB Lambda probe before ***, temperature).


When i got home I performed a boost leak test to 12 psi and no leaks. Inspected all vac lines, etc. Drove it after and still only get 2-3 psi boost and whine/ moaning is still there when attempting to build boost.

Logs here show a short WOT hit (17_58_58) to show boost rising as normal right after leaving work. Then I got the codes above a few mins later. Then second log (18_05_28) a few mins after that, showing boost only 2-3 psi at WOT. Then a couple from tonight after boost leak test, showing low boost. (21_25_34) shows reduced boost target, and (21_25_49) shows boost target back up.

I am at a loss. Could a failed O2 sensor cause reduced boost?

Thanks in advance.
Attached Files
File Type: csv 2017-07-13 17_58_58.csv (3.4 KB, 39 views)
File Type: csv 2017-07-13 18_05_28.csv (5.2 KB, 47 views)
File Type: csv 2017-07-13 21_25_34.csv (4.2 KB, 44 views)
File Type: csv 2017-07-13 21_25_49.csv (4.7 KB, 56 views)


2017 AMG C63 -JB4
2009 535i - 548whp - sold

Last edited by LessIsMore; 07-16-2017 at 08:43 PM..
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Default 07-13-2017, 10:11 PM

Also here is a log from yesterday, showing typical behavior.
Attached Files
File Type: csv 2017-07-12 15_41_03.csv (5.8 KB, 38 views)


2017 AMG C63 -JB4
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Default 07-13-2017, 10:24 PM

whine noise is a leak either from the outlets to the intercooler or intercooler to charge pipe. take them out and inspect the hoses and clamps. i just had the same issue yesterday and today i found a hose from the outlet to the intercooler broken under the clamp. i would had not been able to see it if i wouldnt take them out and check them out the car.

https://ibb.co/eWB5nv
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Default 07-14-2017, 06:54 AM

Quote:
Originally Posted by n5418102
whine noise is a leak either from the outlets to the intercooler or intercooler to charge pipe. take them out and inspect the hoses and clamps. i just had the same issue yesterday and today i found a hose from the outlet to the intercooler broken under the clamp. i would had not been able to see it if i wouldnt take them out and check them out the car.

https://ibb.co/eWB5nv
I can check that. I was convinced I was going to find a leak for sure during the leak test, but I found no sign of it up to 12 psi (except for the normal turbo inlet leak that always shows up around that pressure). Did the test 4 times.


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Default 07-14-2017, 03:43 PM

Okay, I have checked the intercooler pipe and outlet connections, and all of them are tight with no signs of any leaks or tears. Also I confirmed that the vacuum lines are firmly attached to the wastegates.
I also removed and disassembled both Forge diverter valves and checked their operation, both seemed fine.
Also should mention, both of the Boost solenoids are new and less than 2 weeks old. All vac lines going to and from the solenoids are tight and fully seated as well.


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Default 07-14-2017, 08:19 PM

If you have an o2 sensor fault stored the motor isn't going to run properly. So address any fault codes first. Then evaluate the tuning.


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Default 07-15-2017, 08:21 AM

I did some vacuum testing :
  • Vacuum to WG/Boost solenoids (Engine running,through canisters): 23" F and 22" R
  • WG/Boost Solenoid vacuum draw to WG actuators at idle: 26" F and 26" R
  • WG Actuator function: Both close with vacuum. Rear actuator I could see took 10" to fully close, and Front actuator could not see but heard it open/close.
  • WG Actuator vac hold: both hold 10-12" of vacuum with no loss of vacuum.

I took a video of the sound the car is making:

https://www.youtube.com/watch?v=XVrzGaHCaHg


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Default 07-15-2017, 08:26 AM

Quote:
Originally Posted by Terry @ BMS
If you have an o2 sensor fault stored the motor isn't going to run properly. So address any fault codes first. Then evaluate the tuning.
I hear you on that Terry, but the low-boost situation was more pressing and didn't seem like it would be caused by an 02 sensor code.

With that said, I have the 02 sensors and plan to replace them today.


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Default 07-16-2017, 10:44 AM

I replaced precat 02 sensors on both banks, removed/cleaned/regreased DVs, and had them vent to atmosphere so i could better hear what theyre doing under wot.
No change.
Does not appear that DVs are opening under WOT.

Took a video:
https://youtu.be/axjEHW83uzU

Im ki d of suprised a 30FF code hasnt shown up.


2017 AMG C63 -JB4
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Last edited by LessIsMore; 07-16-2017 at 10:53 AM..
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Default 07-16-2017, 08:18 PM

To eliminate tuning/settings as possible cause, I uninstalled JB4 completely and flashed MHD back to stock map. Put stock TMAP back on.

Checked codes with MHD, no errors at all. (after I remembered to put the stock Tmap back on and clear the resulting 2ABD , oops!)

No change, stil a loud wooing and inability to build boost or accelerate well. Its very slow at WOT. Still not generating any codes.

Is the 10" actuator pressure too high?

Started wondering what are the chances its a clogged c_talytic con_erter that just won't allow enough air through fast enough? Maybe it was dying and finally collapsed ...


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