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Thread: Concerns on boost and misc

  1. #1
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    Exclamation Concerns on boost and misc

    I will go ahead and first apologize for this long post, but looking for some ideas/suggestions from the collective super minds on the board.
    To get some useful information back, I think it is important to provide enough detail, and some history.

    History:
    The RS6 had been garaged for about 3 to 4 weeks; it started up fine. Took it for about 20 minute city drive and parked it again. Decided that I need to take another drive, and the car would not start. It would crank up, but not fire up. Turning the key I would see the battery registering above 12V (center line), and during start attempt dip to 8. At this stage I figured I'd leave it alone, order a new battery and spark plugs.
    Next morning I take the keys to the garage anyway, and start up the RS6. It starts up just fine. Take it to work. Go pick up lunch, which is about a 5 minute (3 mile) ride. When I get back to the RS6, it won't start again. Same as before. I call a friend, I hook up the battery cables, and car starts. I figured I have it figured out, and a new battery is needed.
    I get the battery and spark plugs, and I changed them over the weekend. I also did the the RS6 Sportec lower air vent mod.
    After all this work is done, I have not had any issues starting the car up, and has been at least 1+ week since. Took the car to work. Took the car on short drives. Stop and restarts no issues. I figured I was done.
    At this stage I am still running on a tank of gas that was in place even while the car was parked. No new gas has been added.


    Issue:
    After car has been strong for a few days, on my way home from work, after about a 15 minutes (possibly 5-7 miles of city driving), the car jerks a bit.
    Continues to drive no issues for another 2 minutes and it jerks about another mile or so down the road. Afterwards no issues for about 15 or so minutes. I think I might have gone about 7 miles or so. Lights are horrible during my drive. I feel another jerk, and this time a bit stronger than the last one.
    Keep in mind that the jerk was no associated with any downshift or upshift. I could have been going anywhere from 15 MPH to 40 MPH at each of the occurrences. The jerk itself felt more like the engine chocking, and not a tranny issue.
    I pull to a parking lot, take out my Mobile VagCom, plugged it in and connected with my iPhone. No tranny DCTs found. I feel good. However there were engine DCTs as shown further below.
    I am thinking at this point I either have some possible bad gas, or something else is messed up, such as my spark plug installation. Or even bad spark plug.
    One other point to make is when I felt the first jerk, I was accelerating slowly behind a couple of other vehicles, and with the windows opened, I heard what it sounded like air being rushed through a small opening. I had not noticed this before, but it could be me. Also unsure what level of sound difference the lower air vent mod contributes.

    I save the codes and clear them. Take it to the highway for a 5 minute drive from work to home.
    All working just fine, and no issues. As I am about to take the exit, all bells and lights in the dashboard go off, the last I saw was the oil icon large in the center dash, and car shuts down. Given my momentum, I am able to exit the highway and enter a parking lot. Damn the steering is heavy, but made it.
    Park the car, check for leaks and nothing. Spent 5 minutes around the car. Turn it back on, and it starts just fine. Check the DCTs, and the same ones appear.

    Get home fine as I am about 2 miles or so away. No more issues, jerking or shutting down.
    I check the whole car again, and various modules on the car.
    I go online and research the codes. Main concerns appear to be a leak, which is interesting enough based on the sounds I had original heard before. So I get a few details to log, sector 115 (the boost), and MAF readings
    So now I grow a pair, and about 15 minutes go after all the checking and rechecking. I load the wife up in the car, she is in charge of the computer logging with the VAG tool, and also checking to hear anything.
    We end up going for a few runs, as there are a couple of choices around town to proceed with caution. Car is strong again. No more leaking sounds. No more jerking and chocking. No more DCTs after the last clear.

    Needless to say, MAF readings appear to be quite healthy, idling at 5g/s, and on the top end reaching north of 250g/s.
    The boost appears good. I am adding some excerpts below.


    Engine Fault Codes:
    5 Faults Found:
    17535 - Fuel Trim; Bank 1 (Mult)
    P1127 - 002 - System too Rich - Intermittent
    17537 - Fuel Trim; Bank 2 (Mult)
    P1129 - 002 - System too Rich - Intermittent
    17544 - Fuel Trim: Bank 1 (Add)
    P1136 - 001 - System too Lean - Intermittent
    17546 - Fuel Trim: Bank 2 (Add)
    P1138 - 001 - System too Lean - Intermittent
    16705 - Engine Speed Sensor (G28)
    P0321 - 008 - Implausible Signal



    Questions:
    1. One of the runs, I have an actual boost spec request at 24PSI, but the actual was 28PSI. Is this normal for our RS6? My car has stock ECU, and never been tuned. First boost graph ranges from 14PSI to 21PSI
    2. The codes, that were generated based on the jerk/sputtering, any idea what it could be? Do I need new MAFs? Should I change the engine coolant temperature sensor and fuel regulator sensor? Could it be a leak somewhere that I've yet not found, but will be looking for.

    Thanks for any help you can provide. Sorry for being long on the details.


    Here are my boost graph excerpts from my run.



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  2. #2
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    Could we see the logs.

    Recheck maf connectors

    Need to see specified and actual boost

  3. #3
    Registered User lswing's Avatar
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    Your boost is WAY off the charts. Stock is around 8-9psi, running 15-16psi here with great power gains. Fuel filter, ECU cable, bad gas, intermittent air leak?
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  4. #4
    Registered User MaxRS6's Avatar
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    Possibly a split or leak in the waste gate hoses, or bad N80 valve. It should have thrown overboost code with those numbers and gone into limp mode.
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  5. #5
    Registered User 4everRS's Avatar
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    Quote Originally Posted by lswing View Post
    Your boost is WAY off the charts. Stock is around 8-9psi, running 15-16psi here with great power gains. Fuel filter, ECU cable, bad gas, intermittent air leak?
    The reading is not compensating for atmospheric pressure. 2000 mbar converted to psi is about 29psi. Atmospheric pressure is probably about 950mbar where the OP is at. So take 13.77 away from those readings
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  6. #6
    Registered User 4everRS's Avatar
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    I would very MAF sensors are either bad, or not seated/connected properly
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  7. #7
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    On my way out today, the car decided to just call it quits as soon as I hit the work parking lot.
    I figured I'd have it towed at this point to the dealer. I will check what they say, however I am 10 times more inclined to go with the great response I got on this board.

    Thank you again. I will continue to update the post with all details as more become available. Very much appreciated the great feedback.

  8. #8
    Registered User marklar182's Avatar
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    Quote Originally Posted by 4everRS View Post
    I would very MAF sensors are either bad, or not seated/connected properly
    Strong 2nd. Probably the air box is not seated.
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  9. #9
    Registered User Beardown1's Avatar
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    If everything above checks out it could be the alternator voltage regulator. Just a thought.
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  10. #10
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    Yuuuup


    ......

    Quote Originally Posted by Beardown1 View Post
    If everything above checks out it could be the alternator voltage regulator. Just a thought.

  11. #11
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    I just figured I'd check the EBahn manual about the G28 Engine Speed Sensor, and here how it describes it:

    Function:
    The Engine Speed (RPM) Sensor G28 detects RPM and reference marks.
    Without an engine speed signal, the engine will not start. If the engine speed signal fails while the engine is running, the engine will stop immediately.


    I think this sounds like a strong start of a fix to my issue. I already instructed the dealer to make this change.

  12. #12
    Registered User kbvagtech's Avatar
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    Yes absolutely sounds like a failing crank position sensor. Check connections and wiring to G28

    Post MVB 32 readings as well.

  13. #13
    Registered User hahnmgh63's Avatar
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    Check the connections to the Engine Speed Sensor, also remove if able and check to make sure it is clean. I would almost agree with some multiple posts on the board in that your latest issue is un-related to your earlier issue. Sounds like during your Spark Plug change the MAF's weren't seated in and they are giving you the reading your seeing. I would re-seat the MAF's, clear the codes, then take it for a short close-in run and recheck the codes, also after rechecking the connections to the Engine Speed sensor.
    16705/P0321/000801 - Engine Speed Sensor (G28): Implausible Signal
    Possible Symptoms
    * Engine shuts off
    * Engine doesn't start
    * Speedometer inoperative
    Possible Causes
    * Engine Speed Sensor (G28) loose
    * Engine Speed Sensor (G28) faulty
    Possible Solutions
    * Check Engine Speed Sensor (G28)
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  14. #14
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    The car is still at dealer. They are changing the Engine Speed Sensor (G28). They had originally thought it would be easier to make this change with engine pulled pulled down, but have since found they can possibly reach the change without it.
    I was trying to verify it on the EBahn manual, and could not see where the engine coming loose was a requirement. Anyone else know where this thing is?

  15. #15
    Registered User 4everRS's Avatar
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    Quote Originally Posted by nene View Post
    The car is still at dealer. They are changing the Engine Speed Sensor (G28). They had originally thought it would be easier to make this change with engine pulled pulled down, but have since found they can possibly reach the change without it.
    I was trying to verify it on the EBahn manual, and could not see where the engine coming loose was a requirement. Anyone else know where this thing is?
    They must have ruled out the MAF's?
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  16. #16
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    I have checked the EBahn manual back and forth, and found 2 locations where the G28 location is mentioned.

    Section 1, which was my first checkout, appears to be at the firewall. Pics:
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    After I kept checking, I also found it connected to the engine, as seen in the below pic:
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    It does see the last pic is the correct location, but the page on the manual references the V8 Bi-Turbo engine of the RS6.
    I keep learning....

  17. #17
    Registered User hahnmgh63's Avatar
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    The second pic above posted by nene is correct on the location. The first pic just shows where the plug connects up on the Firewall. It is an easy swap and definitely doesn't need the engine lowered. I could probably remove the CV splash plate and have it swapped out in 30min or less, and that's only if I was going slow.
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  18. #18
    Registered User Beardown1's Avatar
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    "The second pic above posted by nene is correct on the location. The first pic just shows where the plug connects up on the Firewall. It is an easy swap and definitely doesn't need the engine lowered. I could probably remove the CV splash plate and have it swapped out in 30min or less, and that's only if I was going slow."

    Okay I've been at this for hours....how to heck do you loosen the 10mm bolt holding the G28 sensor? Removing the splash plate didn't help at all. The fricken turbo down pipe is smack dab in the way and trying from underneath I can't get a wrench on it. WTF!!!
    '03 RS6: Full APR EMCS/TCU, Nurburgring Bronze 19x8.5, Freshly Rebuilt Turbos, Gutted Precats, Stern Racing Mounts, SAI Delete, Aux Radiator Delete, Venair Hoses, Koni Yellows.....

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