S3 Boost Gauge Readings

samuelh_888 · Sep 25, 2021

Hello All, on my S3 I have a P3 boost gauge which is plumbed into the inlet manifold.

On idle boost gauges should typically read -20inHg (vacuum).

My gauge always reads -23inHg however recently it’s risen to -17inHg.

When I switch from analogue to OBD port reading it’s 20.2 which is fine, but it’s an electronic reading.

I don’t have any vacuum leaks as the gauge would read 0.

Is there any reason why it would have risen from 23 to 17inHg? Anything to worry about or check?

Car is boosting fine, just not sure why it’s happening.
Cheers

phateuk · Sep 25, 2021

Hmm interesting. Yeah my analogue Turbosmart boost gauge which is piped into a boost tab on the PCV pipe always reads around -23 at idle.
Surely if it's reading at -17 now there must be some sort of a boost/vacuum leak and it's probably minor enough that you don't notice with your car being at Stage2+ power? What sort of figures are you seeing on full boost? I've just had mine taken to Stage2+ at R-Tech and I see it burst upto around 22-23 PSI briefly under heavy throttle and then holds at around 16 which is what Niki said it held on the pressure test before it begins leaking from the oil filler cap (which I assume needs replacing).

samuelh_888 · Sep 25, 2021

phateuk said:
Hmm interesting. Yeah my analogue Turbosmart boost gauge which is piped into a boost tab on the PCV pipe always reads around -23 at idle.
Surely if it's reading at -17 now there must be some sort of a boost/vacuum leak and it's probably minor enough that you don't notice with your car being at Stage2+ power? What sort of figures are you seeing on full boost? I've just had mine taken to Stage2+ at R-Tech and I see it burst upto around 22-23 PSI briefly under heavy throttle and then holds at around 16 which is what Niki said it held on the pressure test before it begins leaking from the oil filler cap (which I assume needs replacing).

It will easily boost to 27psi, 2bar which is about right for the 2+ map on it.
I would had through if there was a vacuum leak, whether small or large the vacuum reading would drop to zero. This is where I’m stumped.

LEE69 · Sep 25, 2021

samuelh_888 said:
I don’t have any vacuum leaks as the gauge would read 0.

-22 is normal anything closer to 0 is a pcv leak. The gauge only reads zero when the engine isn't running.

samuelh_888 · Sep 25, 2021

Hmm, but surely if there was a vacuum leak it wouldn’t give a negative reading or a lower negative? I’ll order a new PCV, gasket and curved hose. The current ones are only 3k miles old but just in case…

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S3 Boost Gauge Readings

samuelh_888

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phateuk

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samuelh_888

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LEE69

07 170 DSG

samuelh_888

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