low specified boost pressure (mbar)

[cullenvb]

hi. i have an '03 rs6. i recently sealed its intercoolers and repaired an unmetered air issue due to a cracked wastegate feed. my concern is the low "specificied boost" log printout i'm getting after 3rd and 4th gear turbo spools. specifically, the highest # i've seen is 1370 mbar (about 6 psi boost). 8 months ago i logged 1,700 mbar of specified boost (2,200 actual).

is this a result of the ECU starting to relearn after a 'clear codes' command? i don't have any faults and the n75 passes the 'click' test. should i pinch the return air pathway of the n75 to see if boost rises during a short drive?

i guess what i dont understand is what's driving the low specified boost numbers? the ecu? my fuel trims are less than 1.5% corrected. no misfires/knock. high grade gas. it does have an MTM ecu.

shouldn't i start to see 100% duty cycles over time and then see these numbers fall to correct for high actual boost numbers?

also,where specifically is the specified boost being measured? the two air mass sensors? thanks in advance.

[cullenvb]

so, amazingly, turns out all i had to do was unplug the negative battery terminal for 15 minutes. car is now scary fast. it's like going from 4.2 a6 to rs6. now - why did this fix the problem?? clearing codes in VCDS had no impact whatsoever. thank you.

[Shoppinit]

That’s totally weird. I never would have thought that disconnecting the battery would have any effect. See if it remains fixed.

Sounds like your car was overboosting in the past. Maybe the ECU was scaling back boost to prevent overboost conditions. Not sure what the criteria are for reverting to normal operation. Maybe the disconnecting of the battery is a coincidence.

[cullenvb]

fingers crossed - three drives later and car remains a rocket (i'm logging each run w/ VCDS so it's not my imagination). you're right that i did have an overboost issue. i corrected it by mistakenly backing off wastegate spring tension for the driver's turbo. backed it off to such an extent that that turbo probably never boosted (but fault went away). the root cause was due to a torn wastegate actuator silicone tube that i sleeved w/ plastic tubing. somehow that leaky repair led to a series of issues which finally were all address this week. so perhaps after x overboost faults the car just went into permanent no-boost mode, not sure. all i know is ecu wouldn't permit the n75 to duty cycle properly and allow the wastegate to fight the strengthening boost pressures. i was truly stuck at 6psi boost (maybe what wastegates are set to as default) until resetting car w/ battery disconnect. it's such a relief to me as i was contemplating pulling the engine again to further troubleshot.