Thoughts on overboost situation - N75/WG circuit likely cause?

Hal_TT::CBP · 01-16-2006, 08:10 AM

My Omori gauge is reading about 0.1B off actual(or is close enough unlike what I initally thought). So, I've been seeing boost spikes to 1.7B for about a month now. Blew a BPV last week and replaced it(audiable rattle/air noise) but the problem persists. Have spoken with a few on this and everything points to the N75/pressure side of the WG(s) as the boost will hold steady if at part throttle(boost < 1B) but once going WOT it has an initial swing to 1.5B(will go higher if I let it) and then settles to 1.3-1.4B depending on pedal position.

If you log req=actual they are almost identical, minus the initial spike. holding boost in 5/6gears has the boost fluctuate about 0.1B 2x per sec with throttle held constant... leaking somewhere on the N75 circuit I think. I have not pressure checked the pressure lines to the WG actuators but will do this this week, also going to try another N75 valve as I've played with mine *a lot* over the years. Car idles and runs fine, even under boost with the exception of the new boost characteristics. I am assuming since it idles well that the spider and associated PCV system are in tact. Also, have had the car on a lift last week and all things there still look new, no housing/DP leaks. There is a slight hiss at the passenger rear on/off/on every few secs but I cannot tell if this is the EVAP line purging or something else leaking. The EVAP does cycle every 30 or so secs(audiable clicks) as expected. Going to pressure check things soon... in stock mode now.

Any thoughts?

dscottjr · 01-16-2006, 08:19 AM

davenew · 01-16-2006, 08:29 AM

When I first bought my car the plastic hose connector at the back of the engine was cracked. I think they're more of a Y shape than T. If you replaced something like diverter valves, doesn't it take xxx many miles for the ecu to adapt?

Hal_TT::CBP · 01-16-2006, 08:53 AM

Hal_TT::CBP · 01-16-2006, 08:55 AM

EdyJun · 01-16-2006, 10:11 AM

I would defiantly do the pressure test and check for leaks.

Have you though of EBC instead of replacing your N75?

Edy

davenew · 01-16-2006, 10:52 AM

EdyJun · 01-16-2006, 10:57 AM

davenew · 01-16-2006, 11:27 AM

EdyJun · 01-16-2006, 11:58 AM

01-16-2006, 08:10 AM	#1
Hal_TT::CBP AudiWorld Super User Garage is empty, add now Join Date: Mar 2000 Posts: 9,755	Thoughts on overboost situation - N75/WG circuit likely cause? My Omori gauge is reading about 0.1B off actual(or is close enough unlike what I initally thought). So, I've been seeing boost spikes to 1.7B for about a month now. Blew a BPV last week and replaced it(audiable rattle/air noise) but the problem persists. Have spoken with a few on this and everything points to the N75/pressure side of the WG(s) as the boost will hold steady if at part throttle(boost < 1B) but once going WOT it has an initial swing to 1.5B(will go higher if I let it) and then settles to 1.3-1.4B depending on pedal position. If you log req=actual they are almost identical, minus the initial spike. holding boost in 5/6gears has the boost fluctuate about 0.1B 2x per sec with throttle held constant... leaking somewhere on the N75 circuit I think. I have not pressure checked the pressure lines to the WG actuators but will do this this week, also going to try another N75 valve as I've played with mine a lot over the years. Car idles and runs fine, even under boost with the exception of the new boost characteristics. I am assuming since it idles well that the spider and associated PCV system are in tact. Also, have had the car on a lift last week and all things there still look new, no housing/DP leaks. There is a slight hiss at the passenger rear on/off/on every few secs but I cannot tell if this is the EVAP line purging or something else leaking. The EVAP does cycle every 30 or so secs(audiable clicks) as expected. Going to pressure check things soon... in stock mode now. Any thoughts? __________________ Hal. My German car history... '11 S4 Premium +, 6sp, Ti, Nappa, Carbon, SportDiff, B/O, Nav/Park current Audi '01.5 S4 Shizzle #3 ... purchased 09/03/10, Nogaro/Blue Sport '10 Dodge DS Gen4 Ram 1500(designed by Germans lol) '03 TT 225QC ... sold 09/23/10, Ocean/Sea '01.5 S4 APR Stg3 ... sold 09/10/08, Silver/Silver '01.5 S4 Ordered, Silver/Silver, Lemoned 5mos after purchase '00 996 Cab, Blk/Blk on Silver '98.5 A4 QMS Avant, Santorin/Ecru with blue trim '96 Jetta GLX VR6 '95 Jetta GLX VR6 '92 E36 Coupe - Lemoned 4mos after purchase

01-16-2006, 08:19 AM	#2
dscottjr AudiWorld Super User Garage is empty, add now Join Date: Sep 2002 Posts: 14,593	Sounds like you're on the right track. n75s seem to be a bit sketchy after they've been tweaked. __________________ 00 S4, Euro spider hose mod!! 04 allroad, needs rs6 intercoolers, k04s and a cargo box...

01-16-2006, 08:29 AM	#3
davenew AudiWorld Super User Garage is empty, add now Join Date: Feb 2004 Posts: 7,829	does your car have the plastic wg hose tees? When I first bought my car the plastic hose connector at the back of the engine was cracked. I think they're more of a Y shape than T. If you replaced something like diverter valves, doesn't it take xxx many miles for the ecu to adapt? __________________ '00 S4 EPL Stg 3 (March'04-May'08) '08 BMW 135i Dinan Stg 2 (May'08-Present) '00 S4 Imola widebody, ASP GT28

01-16-2006, 08:53 AM	#4
Hal_TT::CBP AudiWorld Super User Garage is empty, add now Join Date: Mar 2000 Posts: 9,755	I think mine are plastic(Y's)... going to check these when I can let it sit a bit. Thx Dave. __________________ Hal. My German car history... '11 S4 Premium +, 6sp, Ti, Nappa, Carbon, SportDiff, B/O, Nav/Park current Audi '01.5 S4 Shizzle #3 ... purchased 09/03/10, Nogaro/Blue Sport '10 Dodge DS Gen4 Ram 1500(designed by Germans lol) '03 TT 225QC ... sold 09/23/10, Ocean/Sea '01.5 S4 APR Stg3 ... sold 09/10/08, Silver/Silver '01.5 S4 Ordered, Silver/Silver, Lemoned 5mos after purchase '00 996 Cab, Blk/Blk on Silver '98.5 A4 QMS Avant, Santorin/Ecru with blue trim '96 Jetta GLX VR6 '95 Jetta GLX VR6 '92 E36 Coupe - Lemoned 4mos after purchase

01-16-2006, 08:55 AM	#5
Hal_TT::CBP AudiWorld Super User Garage is empty, add now Join Date: Mar 2000 Posts: 9,755	Yeah, wish audi had done a three wire with self-diagnosis... __________________ Hal. My German car history... '11 S4 Premium +, 6sp, Ti, Nappa, Carbon, SportDiff, B/O, Nav/Park current Audi '01.5 S4 Shizzle #3 ... purchased 09/03/10, Nogaro/Blue Sport '10 Dodge DS Gen4 Ram 1500(designed by Germans lol) '03 TT 225QC ... sold 09/23/10, Ocean/Sea '01.5 S4 APR Stg3 ... sold 09/10/08, Silver/Silver '01.5 S4 Ordered, Silver/Silver, Lemoned 5mos after purchase '00 996 Cab, Blk/Blk on Silver '98.5 A4 QMS Avant, Santorin/Ecru with blue trim '96 Jetta GLX VR6 '95 Jetta GLX VR6 '92 E36 Coupe - Lemoned 4mos after purchase

01-16-2006, 10:11 AM	#6
EdyJun AudiWorld Super User Garage is empty, add now Join Date: Dec 2002 Posts: 2,719	Re: Thoughts on overboost situation - N75/WG circuit likely cause? I would defiantly do the pressure test and check for leaks. Have you though of EBC instead of replacing your N75? Edy __________________ 2000 Audi S4 STG 3 FATS = 3.66 w/ 91 oct AIM: EdyJun 11 September 2001 In their honor. In their memory. <font color="red">---------------------------------------------------------- <u><big> <a href="http://homepage.mac.com/edyjun1/S4/index.htm">EdyJun's S4 Directory (FAQ, DIY, Info, Tips and Help) </a> </big> </u>---------------------------------------------------------- </font>

01-16-2006, 10:52 AM	#7
davenew AudiWorld Super User Garage is empty, add now Join Date: Feb 2004 Posts: 7,829	ebc with apr? good luck:) __________________ '00 S4 EPL Stg 3 (March'04-May'08) '08 BMW 135i Dinan Stg 2 (May'08-Present) '00 S4 Imola widebody, ASP GT28

01-16-2006, 10:57 AM	#8
EdyJun AudiWorld Super User Garage is empty, add now Join Date: Dec 2002 Posts: 2,719	Oops, didn't realize Hal_S4Shizzle::CBP had ARP. __________________ 2000 Audi S4 STG 3 FATS = 3.66 w/ 91 oct AIM: EdyJun 11 September 2001 In their honor. In their memory. <font color="red">---------------------------------------------------------- <u><big> <a href="http://homepage.mac.com/edyjun1/S4/index.htm">EdyJun's S4 Directory (FAQ, DIY, Info, Tips and Help) </a> </big> </u>---------------------------------------------------------- </font>

01-16-2006, 11:27 AM	#9
davenew AudiWorld Super User Garage is empty, add now Join Date: Feb 2004 Posts: 7,829	hey, I left my ebc wired up (all but power).. so if anyone figures it out let me know:) __________________ '00 S4 EPL Stg 3 (March'04-May'08) '08 BMW 135i Dinan Stg 2 (May'08-Present) '00 S4 Imola widebody, ASP GT28

01-16-2006, 11:58 AM	#10
EdyJun AudiWorld Super User Garage is empty, add now Join Date: Dec 2002 Posts: 2,719	If i find it i will post and add it to my site. __________________ 2000 Audi S4 STG 3 FATS = 3.66 w/ 91 oct AIM: EdyJun 11 September 2001 In their honor. In their memory. <font color="red">---------------------------------------------------------- <u><big> <a href="http://homepage.mac.com/edyjun1/S4/index.htm">EdyJun's S4 Directory (FAQ, DIY, Info, Tips and Help) </a> </big> </u>---------------------------------------------------------- </font>

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