Help car wont boost past 0 psi

[owneraudis4]

I have a stage 3+ 2000 S4 with frankenturbo's. This build has taken forever and I just can't seem to get the car working right. I finally don't have a check engine light anymore after getting rich codes and Josh at solo motorsports fixing the tune so that I do not have a CEL anymore. But the car still seemed slow I installed a VIDI boost gauge yesterday and the car will not boost past 0 psi. It has vacuum at idle -21.0 but when I apply throttle it will go to 0.0 psi and will not more past it. My mechanic installed a new N75 valve could that be hooked up wrong or defective. Any help would be appreciated!

[Corradovolksb]

If your not building any boost it sounds like you have a large boost leak but if you did the car would not run well at all. This may be a crazy question but do you have a one way check valve inline with the boost gauge not allowing it to read boost? Where did you hook the vacuum line up to the intake manifold?

[owneraudis4]

It's a vidi electronic gauge that pulls the info from the obdII it is not a manual gauge. The car is running super smooth just won't build boost.

[Corradovolksb]

I don't think that gauge will read boost because the ECM does not produce a signal that can be read by an obd style boost gauge. I think you need to add the boost pressure sensor to that gauge to make it work correctly. Have you done any logs?

[owneraudis4]

I haven't done any logs yet just got my ross-tech vcds. But that gauge is designed to work with the B5 S4 vidi said no manual gauge needed should pull the boost information right from the obdII. If it didn't work seems like it wouldn't work at all it is reading -21 at idle and building to 0.0 but wont go paste 0.0. And the car feels like it isnt building any boost feels like all motor.

[getslideways]

As suggested, check the observed boost pressure with VagCom to verify what the VIDI boost gauge is displaying

[Corradovolksb]

With VCDS go to measured value 115 and the actual boost should be equal or close to requested. It will be in mbar without atmospheric correction so subtract about 950mbar or whatever the actual value is reading at idle from the value and that will give you your actual boost in mbar then put a decimal point after the first number if it's a 1 or in front of the number of its less than 1 and multiply that by 14.7 to get an aprox boost level. Or you can put that mbar into an mbar to psi converter like the units app.

[CELison]

Wastegate(s) nut(s) backed off is my guess.

[bl0wn3ur0]

I had a friend with the same issue and he had broken wires on one of his primary o2 sensors. We fixed that and he went right back to 22 psi


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[owneraudis4]

If I had broken wires on my primary o2 wouldn't I be throwing a check engine light?

[CELison]

I had a friend with the same issue and he had broken wires on one of his primary o2 sensors. We fixed that and he went right back to 22 psi


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That is impossible. 0 boost, not wg pressure.

[bl0wn3ur0]

That is impossible. 0 boost, not wg pressure.

You say it's impossible yet it happened sooooo

[Royal769sr]

I had a friend with the same issue and he had broken wires on one of his primary o2 sensors. We fixed that and he went right back to 22 psi


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This was my case

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[Royal769sr]

With my o2 no getting any signal it would barely boost. Normally it's hitting 26psi.

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[CELison]

Barely and 0 are very different.

[Zba]

To boost zero psi means you have an issue with the turbo. Could have a fucked up turbo or wastegate