Some of the P3 gauges for various cars have them integrated and read from the OB port as long as you select the option. Mine does not have the “boost tap”.
From their website:
“Specifically designed to support the Audi B7 A4 / S4 / RS4 platforms. Reads boost and all data directly from the diagnostics port for fast plug and play install.”
EDIT: changing the title of this thread.
A4 = boost from ECU
RS4 = no boost to read from ECU
Sometimes I am amazed how clueless people are.
Maybe I was wrong to think it’s obvious lol so let’s just be clear. The RS4 was not boosted from the factory. There’s no boost function/sensor. You need to tap in to read boost. Same goes for B67 S4
The B7 A4 2.0T and the TDI offerings all came boosted and have a boost sensor feeding the ECU which you can then read directly from the obdii.
one note is that some N/A cars come with MAP sensors, the new Audi N/A motors did not though
http://www.volkspage.net/technik/ssp/ssp/SSP_377.pdf page 38
wonder if it (the gauge) attempts to correlate pressure from mass flow signal and IAT signal?
Funny how my p4 gauge has no boost dongle and still reads boost by only tapping into the OBII port. I just installed it last week and there is nothing more to it than plugging into the port. Reads boost, plain and simple. Do I need to take a video of the install and reading for those who have neither seen the gauge, installed it, or used it??? Holy fuck.
Also, depending on how long Alex has had his gauge, as I read he mentioned he has the boost dongle, he may have the older version of the gauge. There is now an updated version which is what I have and it has an internal sensor of some sort that reads from the ecu.
I too am amazed at how clueless some people are. Some idiots will refuse to acknowledge it’s daylight out when the sun is shining in their face.
The intent of my original post was to repudiate any claims by AMD that the gauge is reading high as it reads right from the ecu, however, it seems there may (or may not) be some possibility of truth there depending on whether or not it reads from the ecu, like mine, or from a boost tap, like Alex’s. The external boost tap may introduce a margin of error, but as Alex has stated, his was dead-on accurate.
Axel, not Alex, sorry for the misrepresentation.
based on this…
Holy fuck, yes, you do . You’re saying it works just fine…but only shows 2 PSI all the time?
Is there an edit option for posts?
Well in case it was missed in my jumbled post above quoting Saki:
My car is limited to 5500 rpm and other limiting controls right now during the engine break-in procedure. Boost is boost and the gauge is reading it, period.
Need to reach 150 posts first.
We really need to alert new members of this rule. I think I’ve posted this dozens of times now lol
Does it also read vacuum or change readings?
Apparently I wasn’t very clear when I said, “Unfortunately mine only reads 2 psi right now.”
That 2 psi reading is not constant. It reads vacuum you can clearly see it when it starts to build boost. Also, the gauge is configured to read boost in digital mode, i.e., directly from the OB port. You can select the gauge to read in analog mode and that would require a boost boost tap. Axel may have also unnecessarily bought and installed the boost tap too, but like I said, the gauges have been updated.
From their site:
Why is there an optional analog boost sensor on VW/Audi models?
We offer this option for people who are replacing an existing gauge or for some reason prefer analog readings over ECU readings. If you decide to use an analog sensor instead of reading boost via the diag port as by default, you would need to purchase a boost tap for your engine. For the vast majority of our customers the boost/vacuum readings from the diagnostics port are used. You can switch between analog and diagnostics port readings via the config menu.
The P3Cars VIDI is designed to do everything you need right out of the box, but we do occasionally make updates to add additional support for more engines/car types, values, or bug-fixes. Software updates for gauges made after Feb 2012 are available as a user replaceable memory chip for $25 or free for bug fixes. Gauges made before Feb 2012 require a hardware update, please contact us for details.
Analog Boost Sensor
Product description
Price:
$30.00
SKU:
P3ABS
Quantity:
Product Description
Optional external analog boost sensor add-on. Not compatible with e9x or e8x gauges which already have built in sensors. For use only on P3 Cars gauges.
With the internet sleuthing ability of some on this site, you’d think readily available information from a manufacturers website would not need to be referenced here over something so obvious.
Who is being argumentative now?
I’m really curious as to which blocks it’s reading to provide boost info on a car that didn’t come with boost.
Edit: I may have found it: http://www.ross-tech.com/vag-com/m_blocks/110-119.html
I’m going to have to do some block measuring for shits and giggles this weekend 
The point we are trying to make is…the ECU can only read boost through a sensor meant to read air pressure. So unless they set up some kind of backwards calculation using other parameters you would need the boost tap. I wonder how accurate it would be it the calculation thing was the case.
Fixed.
Where is it reading boost? None of that makes sense.
Better tell APR as well…that they’re wrong.
Being that I have seen more of this engine than I like to admit, I can assure you there is NO MAP sensor, which if VAGCOM was reading boost directly…that is what it would most likely be using.
You have absolutely no clue how it reads boost, you just know it does…otherwise you’d explain it to me. It wouldn’t be hard for them to program some BS backwards calculation off of the MAF reading. But they would need to use very specific information about the engine to be accurate, or they could use very generic info so that the customer sees their gauge dance and are happy.
Ultimately, I have two different boost gauges. I can do some VCDS logging and see if there’s any discrepancy between the two gauges and VCDS to see how accurate the ECU reading is. If it’s spot on, fantastic. If there’s a margin of error, we should be able to see by how much and whether it’s linear or exponential.