Boost stops at 1.4bar - N75?

[hunker7]

Hi. I have a problem, my AAN won't boost past 1.4 bar (gauge), sometimes will tick to 1.5 and that's it. As before, it juddered when reaching 1.4/1.5, after I changed fuel lines, it just stops boosting, but runs without any problems otherwise. Before I had vacuum in the tank.

Just checked all the usual hoses that might have cracks, nothing, refitted them with new fasteners. I did notice oil in Michelin man hose

No error codes coming up either.

After reading on here and other places, N75 can be tested by removing middle vacuum line, and it should boost past 1.5 if faulty, correct me if I'm wrong, and if electric plug is removed I shouldn't see more than 0.4 bar?

Thanks a lot for help in advance

P.S. Don't be harsh, this is my first Turbo car

[rxl]

Hi. I have a problem, my AAN won't boost past 1.4 bar (gauge), sometimes will tick to 1.5 and that's it. As before, it juddered when reaching 1.4/1.5, after I changed fuel lines, it just stops boosting, but runs without any problems otherwise. Before I had vacuum in the tank.

Just checked all the usual hoses that might have cracks, nothing, refitted them with new fasteners. I did notice oil in Michelin man hose

No error codes coming up either.

After reading on here and other places, N75 can be tested by removing middle vacuum line, and it should boost past 1.5 if faulty, correct me if I'm wrong, and if electric plug is removed I shouldn't see more than 0.4 bar?

Thanks a lot for help in advance

P.S. Don't be harsh, this is my first Turbo car

what boost do you need to see? what setup do you have?
if the wasgate spring is stock you will only have 0.4bar bost...
if you boost that hi it will not bet the n75...

[hunker7]

Mine is stock, well, AAN should se 2.1/2.2bar on full boost afaik.

So I should see 0.4bar if I unplug N75?

[Ross]

It's 2.1/2.2 absolute assuming stock etc, 1.2/1.2 gauge.

If you're referring to the dash then that is absolute and 1.4 is equal to 0.4 gauge which is what you would see with the N75 unplugged or if it's in limp home mode. Sounds like you've got a problem and need to pull codes.

[rxl]

Mine is stock, well, AAN should se 2.1/2.2bar on full boost afaik.

So I should see 0.4bar if I unplug N75?

if its stock its the right boost.. or do you have any other problems?

[rxl]

oh 2.1 2.2 you will never see..

[hunker7]

It's 2.1/2.2 absolute assuming stock etc, 1.2/1.2 gauge.

If you're referring to the dash then that is absolute and 1.4 is equal to 0.4 gauge which is what you would see with the N75 unplugged or if it's in limp home mode. Sounds like you've got a problem and need to pull codes.

Yes, I was getting 2.1bar absolute before, now 1.4bar absolute.

pull codes? vagcom won't show any error codes.

[hunker7]

oh 2.1 2.2 you will never see..

2.1/2.2bar absolute, so 1.1/1.2 gauge.

[newsh]

Sounds like N75 is already unplugged.

[newsh]

Except that would show a code so maybe stuck. Can you hear (or feel) the WGFV ticking when you blip the throttle?

[hunker7]

Except that would show a code so maybe stuck.

Would removing middle vacuum line would allow it to boost over 1.4/5?

WGFV?

[newsh]

With the WG connected to the face of the turbo then the spring will compress and open the gate at 0.4Bar of boost (1.4Bar absolute on your dash). The exhaust gases pass though the WG and into the exhaust without passing through the hotside so that boost is limited.

To get more than 0.4Bar of boost the ECU comes into play, at full throttle the ECU starts to control the WGFV.

What the frequency valve does is to modulate the pressure from the face of the turbo to the WG so the WG "thinks" it is getting less than 0.4Bar and so closes allowing more exhaust gases to pass through the hotside therefore creating more boost.

If you disconnect the WG from the turbo by pulling off the pipe at the banjo on the WG and plugging the end, it will keep on boosting for as long as you hold the throttle open till it blows up. This doesn't really prove anything though.
You either have no active boost control because the WGFV is broken or because the ECU is not giving it for some reason (which would normally show a code)

[hunker7]

With the WG connected to the face of the turbo then the spring will compress and open the gate at 0.4Bar of boost (1.4Bar absolute on your dash). The exhaust gases pass though the WG and into the exhaust without passing through the hotside so that boost is limited.

To get more than 0.4Bar of boost the ECU comes into play, at full throttle the ECU starts to control the WGFV.

What the frequency valve does is to modulate the pressure from the face of the turbo to the WG so the WG "thinks" it is getting less than 0.4Bar and so closes allowing more exhaust gases to pass through the hotside therefore creating more boost.

If you disconnect the WG from the turbo by pulling off the pipe at the banjo on the WG and plugging the end, it will keep on boosting for as long as you hold the throttle open till it blows up. This doesn't really prove anything though.
You either have no active boost control because the WGFV is broken or because the ECU is not giving it for some reason (which would normally show a code)

Thanks for the info mate. So my best bet is faulty WGFV, as it only gets spring boost?

[newsh]

I would say so, I'm not sure if there is another condition that causes no active boost control on the urS4/6, Dave will be along in a bit to tell us. Maybe the MFTS (Multi Function Switch) under the water manifold. You could try unplugging that and see if your boost comes back.

BTW.. Did you try blipping the throttle and seeing if the WGFV ticks?

[hunker7]

I would say so, I'm not sure if there is another condition that causes no active boost control on the urS4/6, Dave will be along in a bit to tell us. Maybe the MFTS (Multi Function Switch) under the water manifold. You could try unplugging that and see if your boost comes back.

BTW.. Did you try blipping the throttle and seeing if the WGFV ticks?

Haven't tried anything, will do tomorrow and see what it does. As I said before, at first it had a power loss sort of thing when it hit .5 bar, but now just won't go further.