air mass sensors giving different readings, rs6 c5.

[cullenvb]

has anyone checked their 2nd measuring block in the engine module of VCDS?

i'm curious to see if my readings are in line with other RS6 owners. specifically my mass air flow bank 1 reading is typically nearly double (say 4 g/s at idle) to mas air flow bank 2 (say 2.5 g/s).

i've taken logs of the two fields and the general trend is bank 2 (driver's side) lags in measurable airflow and drops much more precipitously when off boost, vis-a-vis bank 1.

i can provide log data if need be. initially i suspected an airleak after the sensor but i can't find one.

i've removed / plugged the crankcase breather system and that had no impact on the values. switching the meters doesn't change the values, so they're not causing the difference.

i've removed the airflow meters off of the air intake filter and rocked them to see if air was creeping in behind the rear air guide's rubber seals. this rocking of the intake senosrs didn't seem to have any impact of the resulting values as the engine idled.

i have no engine faults. my intercoolers are sealed and hold pressure. i'm not sure how to smoke test as between the overrun air recirc. and crankcase tubing and two air mass intakes i don't see a sensible way to build pressure.

according to the piping of the pcv system, the only difference between the two air flows behind the sensors is that the driver's side takes air in from both valve covers whereas the passenger (bank 1) only gets post-sensor air from the crankcase. is this enough of a difference to attribute to the readings i'm seeing?

so if anyone can help me with what they're seeing with their airflows values i'd greatly appreciate it. if my values are normal i'll stop hunting for airleaks. i just don't want to end up pulling the engine again over nothing.

thanks.

[2.ohhh]

Just took my readings this week chasing a rough idle and misfire/lean codes...mine were the same values as yours but flip-flopped...higher on bank 2 and lower on bank 1. I definitely have a vac leak under the manifold, most likely the suction jet pump, but we'll find out for sure in the next few days when it comes apart. I guess my point is my readings were relatively similar to yours, but I was having significant running issues...

[cullenvb]

thanks. i don't have an idle or misfire issue but maybe that's because my issue just isn't as severe. not sure. are you going to take the manifold off with the engine in the car? i've done it, but the engine was out and i remember thinking how much harder it would've been in the car. how are you going to trace the leak? smoke? vacuum pump? does anyone have EGR or vacuum flow diagrams?

[2.ohhh]

I'm going to do it without pulling the motor....others have, so I'm confident that I can too. I've done some pretty hardcore projects in my garage, so as long as it has been documented that it can be done, I'll try that route too. As far as leak tracing, I was using carb cleaner to get an idle reaction, which worked pretty quickly given the choppy idle that I have. I just posted in another thread and it was pointed out that the suction jet pump is most likely the cause...it's a crappy plastic valve that apparently is common to fail on the PCV system that's under the manifold right where I was getting the idle changes with the spray.

If you've had your manifold off, then you know the mess of stuff that's under there...here are the diagrams that I used to visualize the lines that I can't lay eyes on until I remove the manifold....

http://www.oemepc.com/audi/part_single/catalog/au/markt/USA/modell/RS6/year/2003/drive_standart/290/hg_ug/103/subcategory/103090/part_id/262161/lang/e
http://www.oemepc.com/audi/part_single/catalog/au/markt/USA/modell/RS6/year/2003/drive_standart/290/hg_ug/133/subcategory/133040/part_id/252521/lang/e
http://www.oemepc.com/audi/part_single/catalog/au/markt/USA/modell/RS6/year/2003/drive_standart/290/hg_ug/133/subcategory/133041/part_id/253781/lang/e

[cullenvb]

excellent links, thanks. smoke test through the after-run piping solved the mystery. i boogered a repair to a torn tube connecting the N75 to the driver wastegate actuator a year ago. smoke bled out of it when i tested system this week. so air leaked out of it either from the boosted n75 line or the after-run unmetered n75 connection.

long story short - added new silicone tubing wrapped in foil from actuator to connector piece into N75. immediately mass air flow sensors begun to parrot one another. thanks again for all your help - can get lonely trying to troubleshoot alone with no one to guide you.