vtraudt

Installed the hose with ‘jet’ and ‘restrictor’ on my 1.8T AEB with Giac PC16, try to 'disrupt' the boost control circuit.

Installed between N75 and wastegate actuator, the air flow should be significantly reduced (expected result: slow opening wastegate)

Pumping changed as follows:
- No real pumping over 3500 rpm
- Pumping now seems at lower frequency, but still very pronounced
- Boost (if not swinging) is kept around 16-17 psi.
- In 5th gear boost goes to 20 psi at 2200 rpm and stays that way into high RPM. Not sure why (does the ECU 'know' what gear is selected?). Could be Giac put different settings in for different gears?

Still looking for any suggestions to tweak the setup to avoid the massive boost swing (short of putting a MBR in to simply cut the boost, which wouldn't really work either since swinging occurs also at 12 psi).

Note: swinging started when larger turbo (K04/RS4 type) was installed.

vtraudt

More tests done:
- N75 electrically disconnected (no energy, compressor pressure goes to wastegate): 4 psi (on other 2 cars: 4-5 psi, and 7-8 psi (last one has stiffer actuator spring)
- wastegate actuator hose pulled off (no pressure to open wastegate): all cars boost to 20 psi (maybe higher, didn't try), and NO BOOST SWING

conclusion: combination of high flow manifold/larger turbo plus wastegate plus N75/Giac PC16 tune is causing the swing.

I would like to no more what the N75 adjustment screw is doing, what is changing when turning the screw? Does anyone know?

shane0569

If you turn the screw clockwise, it should make the distance that the solenoid valve has to travel less. (Going from full pressure to wastegate ---> no pressure to wastegate) So, I'd imagine tightening the screw would essentially make the wastegate open slightly faster and maybe a little more sensitive.

rares77

hy ! i read your post about the N 75 valve
I have an Audi S4 2.7 Biturbo and here is my problem the car gets low boost untill 3000 rpm. after that rpm it goes exactly like it shoulds.

i put the boost tester on the n75 on the hose that s goes to the westgates and at this rpm 2000 to 30000 it gets discontinious presure near 0.5 bar( the needel just goes from zero to 0.5 bar)
after that 3000 rpm it goes to zero and groves up tu 1.5 bar only when i change gears.
My question to you is
Do you think is an n75 failuere or is a normal comand if something else ( like a sensor ) faild.
on the Wag tester i have no fault code.
Thanke you very much.

Aaron Hoover

Would a bad N75 valve cause a gradual loss of boost over time? I'm now only getting 6psi at the most, a month ago I was getting 7-8psi and in the winter I was getting 19psi, needless to say my boost had dropped quite significantly since then.

chriss08

i just recently bought an a3 1.8t with modifications-
atp top mount turbo manifold
gt28rs turbo
uprated fuel pump and injectors
apr dv
custom map mrctuning
maybe more that im unaware of
running over 300bhp

i bought it with a blown turbo and fitted a new one, the problem is boost! it starts boosting at around 4000 and seems ok in 1st 2nd as im feeding the power on but through the other gears it starts boosting at 4000 as normal but past 5000 it feels like the boost is sputtering on and off, there is some backfiring as it does it, ANY IDEAS!!!! its started to get very frustrating looking for problems

md_medic

I was wondering whether or not the MAF sensor has any control over the boost. Because my boost kept going down from 17-19 to 10 then my MAF just completely ate the dust. No CEL's nothing. So I unplugged it,had 0 boost ( normal @-20 vacuum) ran like a limp worm but got me home. I cleaned the MAF and then it ran normal again when I plugged the MAF in but I am now getting an MAF code and generating maybe 5psi boost tops. PM me if you get a chance

vtraudt

What is the MAF code?
If MAF is bad and throws a code, ECU is putting you into 'limp mode' to safe your sorry a..If MAF is consistenly bad (code returns are clearing code), get new MAF. Car won't run with bad MAF (as you experienced), and ECU will do whatever it takes to prevent you from blowing up your engine (including cutting boost to 'spring pressure' of your wastegate actuator, around 3-4 psi on stock turbos).

md_medic

I am not sure what the exact VAG code was because I had to disconnect it to drive it which of course threw up a code. I am going to put a new MAF in it today. I am, and always have been a Bosch man (I even hate using NGK plugs) but how much difference does a Bosch MAF make over stock. I mean I have a stage II chip 3"turbo back (test pipe) aftermarket turbo inlet pipe FMIC and a stock modified intake with a K&N panel filter (I am normally registering +195g/sec on my mass air flow). Right now money is an issue as I have my eye on a '72 914 and my father (+45 yrs factory trained experience) and I can build a monster engine and they handle well. Anyway the bottom line is I am not sure If I am going to keep this Audi. I love it in so many ways but I would like to find a B6 with a manual as this tiptronic is for the birds. Thanks for your help

Steven Irvine

Hi all, I have a question I hope you can help with. I have an 05 B5. When the car hits approx 65 mph it goes into limp. I have cleaned the maf, egr valve and still no joy. I now feel it could be the wastegate solenoid. IT also blows a lot of black smoke out the back, I know it's diesel but more than I would like. When I say a lot it's not filling the road but noticeable in the dark against the rear cars headlights. I've lost confidence in all my mechanics around me as they can't solve it and I don't want to tKeit to a dealer who I will pay a fortune to and maybe still not get it resolved. Any ideas?