Wouldn’t it be read off the pressure sensor on the manifold? Sensor G71, http://www.audizine.com/forum/showthread.php/488393-The-TRUTH-about-B6-B7-S4-V8-cam-sensor-codes-Diagnosis-help-and-common-problems
Just because those blocks exist, doesn’t mean they will work. 115 should be the MAP reading for cars that have a MAP sensor.
From the damn OB port! For the umpteenth time…Jeezuz.
Come on Saki, you are smarter than that.
Attempting to borrow credibility from APR does not lend credibility to your argument.
As I stated originally, and numerous times since then, the gauge reads boost from the OB port. How it does that, I do not know, nor have I claimed to.
We understand it’s reading the OB port. People are simply wondering exactly which block using which sensor is it pulling its data from.
It’s possible that it’s using a sensor that is not completely accurate, that’s what they’re asking.
I’m offering to cycle through the different blocks, log and measure them while comparing them to two different manual gauges that are directly tapped in (as controls).
No I am not smarter than that. APR posted explicitly on this forum why they can’t report boost numbers without manually adding a boost sensor that measures manifold pressure. Those reasons are the same reasons you are off base.
The car has no boost sensor. The car is not built to measure boost.
Further, if you have a supercharger, where are you going to measure boost? Let’s leave that question to you. Do you want to measure boost before the supercharger? After the supercharger? Before cooling? After cooling? In the manifold? Somewhere else like the MAF?
If you don’t know the answer to these questions…and you don’t know how your gauge is measuring ‘boost’…how can you trust the information to tell you anything? What if it’s measuring your tire pressure 
[quote]6. Is another code that doesn’t always occur. Your car does not have a Baro sensor but uses the MAF to calculate it. This code is caused by the excess reversion of air coming back into the intake from the cams being out and throwing it off. Yes you can get this code for a bad MAF but much of the time it is does to a timing chain issue or other major mechanical failure and accompanied by other codes.
[/quote]
as I suggested before, its probably correlated based on the measured mass flow and air temperature
[quote]16490/P0106/000262 - Manifold / Barometric Pressure Sensor (G71) / (F96): Implausible Signal
Possible Symptoms
Erratic Idle
Possible Causes
Wiring and/or Connections from/to Manifold/Barometric Pressure Sensor (G71)/(F96) faulty
Leak in Air Intake and/or Exhaust
Manifold/Barometric Pressure Sensor (G71)/(F96) faulty
Engine Control Module faulty
Possible Solutions
Check Engine Control Module Software Version
See Special Notes for Details
Check Timing
See Special Notes for Details
Check Wiring and/or Connections from/to Manifold/Barometric Pressure Sensor (G71)/(F96)
Check for Leak in Air Intake and/or Exhaust
Check/Replace Manifold/Barometric Pressure Sensor (G71)/(F96)
Check/Replace Engine Controle Module
Special Notes
On certain smaller Engines we’ve seen cases where a buggy Engine Control Unit Firmware can cause these fault codes, additionally there are known Problems with the Timing Chain Tensioners which can also result in these fault codes. Please refer to the related TPL/TSB for more instructions.
[/quote]
http://wiki.ross-tech.com/wiki/index.php/16490/P0106/000262
Thanks Beem, like I said, I’d be interested in how exactly this gauge is set up to read boost values.
Beem, If they wanted to be accurate, wouldn’t the formula for calculation need to have very specific info about the engine (VE) and blower combo…even then it would still be a calculation and not ACTUAL.
I think’d you’d need some knowledge of the cross-section of the MAF. you measure mass over time and temperature, assume ideal gas you are still left with P ∝ 1/V.
it would also only work if the MAF is being blown through, eg on a roots kit where the MAF is before the blower those measurements will be for the incoming air not the pressurized air leaving the blower. the AMD kit is pull through:
http://avivainstruments.com/images/avivaimages/portfolio/portfolio-rs4sc/2nd/13-perengine.jpg
So what is rxheven gauge showing? Is the odb2 port just outputting the reading from a random pressure sensor? Where is this sensor?
Yea, I know 100% the S4 has no boost measurement sensor. However, the S4’s manifold had a tap accessible that is perfect for adding a line to measure boost from. It was at the back side of the manifold somewhat near the oil housing. That’s how I measured boost with my JHM kit and used a P3 gauge from a BMW (long before they made one for Audi, I tried for 2yrs to get them to make one for the Audi, I even bought and sent those fuckers an oem vent per there request. I have tons of emails about “2weeks and we’ll have a prototype well send ya”).
Turns out…he doesn’t know. Ironically.
Maybe he’ll stop arguing now.
Weird, I wasn’t trying to start a pissing match. I was truly curious how this gauge works and I knew that the B6/7 S4 did not have a “boost” sensor.
I definitely don’t know everything and I learn shit everyday, but some people are way to quick to point out how “wrong” someone is based off of website jargon for that product.
RXHeaven, maybe you should inquire how exactly this reading is measured via OBD like we are implying or actually buy the tap that will be more of an “actual” boost reading.
^^ Yep me too. I am really curious as to what is actually being measured.
I wasn’t arguing. I clearly stated my gauge simply plugs into the port and displays a vacuum and boost measurement. Some of you were arguing that I am wrong about what I bought, installed, and can see with my own eyes. Don’t try to turn it around on me Saki.
Originally I assumed the reading comes from a MAP sensor but that clearly seems not to be the case. I have no experience with these Audi ECU’s, its control systems, or for that matter, MAF’s. The only MAF experiences I have are removing them to toss in the trash or sell on e-bay to replace with 3-Bar MAP sensors for aftermarket ECU’s like Microtechs, Haltechs, a Motech and an AEM. I have wired up many cars with ecu’s over the years and understand how systems work, in general… now if I could only learn to tune them.
I have no problem admitting when I am wrong but something else is going on as my gauge does read vacuum and boost up to 2 psi. In my defense, after reading the product description I was sure, and then referencing it here where it seems to have swayed others, that the gauge did not need the boost tap for these platforms. All that said, I did e-mail the the guys at P3 yesterday and they got back to me this morning. Here is the exchange.
ME
Hi,
The B7 S4 is naturally aspirated and now mine has a supercharger on it. Will your gauge read the boost from the ecu as claimed on the page or does it need a separate boost sensor? Does it end up reading boost from the ecu and if so, how does it do so if the car was not equipped with a sensor originally.
P3
David,
For cars that are not factory boosted, you will need the analog boost sensor option.
Thanks!
ME
I ordered your gauge without the analog sensor because according to the product description, I didn’t need to. The gauge is installed and it is reading vacuum and boost by just plugging into the port??? Audi B7 S4.
P3
David,
If it reads, then your tuner is a smart guy! The gauge will read from the factory sensor if it is able.
So, I don’t know what the fuck is going on. I was never informed how much boost my car is running during this break-in procedure, nor did I ask. I only new it was lower and there were other limiting factors within the tune. I have ordered P3’s boost tap this morning and will show video of the gauges reading with and without the boost sensor to see if they are the same.
He’s contradicting himself. He said you need a sensor if it doesn’t come with one and then says it’ll read it from the sensor if it is able to. Huh? Sounds fishy to me
That is fantastic. That will absolutely compare the two, on the same car and either, the numbers will be slightly different because one is not actual boost and uses different sensors and has to use an algorithm or they’ll be identical, in which case, these other sensors and the algorithm used is spot on which will be a huge help to anyone down the road looking into adding a supercharger as this means they’ll be able to use OBD software (such as P3) to read the blocks.
So your research will help people down the road. Great stuff. Looking forward to the results.
[quote]P3
David,
If it reads, then your tuner is a smart guy! The gauge will read from the factory sensor if it is able.
[/quote]
This
David I would suggest getting a proper boost tap. You are reading a signal from the car for boost. It was for my use only in detuning your car. I generally turn it off before the customers get their cars back.
Sorry guys, I should have said something sooner. Maybe make a new thread on just the reading boost via the port or split this one? I’d rather not post in threads that concern other companies, even if part of that thread includes a JHM customer. If we can split the thread that would be great, if not once everyone has seen this I’ll delete it.
Ok, but which sensors is it reading and how accurate is it? By recommending an actual tap, I’m inferring that it’s not all that accurate but still gives a ballpark figure? Would that be accurate?
My brain just done blowed up :o
I didn’t hear anything? Must have been a small explosion. Like one small bubble wrap pop.
clochner or beem can split out the P3 boost gauge discussion maybe?