does anyone know which blocks on vagcom to use to check these 2 things. I've been searching and playing with the vag but havent found much on this. thanks.

 

I don't think you can check boost on your car. You need a MAP sensor, and those weren't put in until 2000 or 2001.

But on mine, i use block 115 to check requested and actual boost.

 

Thats kinda what I figured , because I can read it on my friends 2000 a4. Do you know if I can read vacuum though.

 

Sorry. I don't know of a way to do that. I don't think it's possible.

 

This isn't true. I can check actual vs. requested boost on a '97 A4 with Vag-Com.You should be able to on your '98. Should be block 115. Block 117 also reports specified boost and 118 reports actual boost.

I don't think you can measure vacuum with vag-com....there may be a way but I don't know it. Search the VWVortex Vag-Com board. You may be able to find a way to do it there.

 

Yeah, but block 115 only lets you see up to a certain point as it maxes at 2450mbar (before altitude correction). So for some of us you can't tell how much more than 2450mbar you're going.
Thanks to Mike (bhvrdr) at another well-knwon audi site:

Channel 115: Requested Boost and Actual Boost

This is a very helpful channel for diagnosing boost leaks, trying to figure out why your car went into limp mode, and seeing if the software or hardware (electronic or manual boost controllers) are doing what they should be. This channel displays the boost requested by the computer (requested boost) in the first column and the boost actually made by the turbo (actual boost) in the second column. The readings you will see here can be misleading. First, you should know that the numbers you will see are not yet corrected for atmospheric pressure (about 1040mbar at sea level). The atmospheric pressure seen at the boost sensor is tough to estimate with complete precision, but I have found that subtracting 1000mbar from the numbers gets you close enough to actual boost unless you are living at 20,000 feet above sea level. The next thing you have probably noticed about these numbers are that they are displayed in mbar instead of psi like we are all used to. Well, this won‼sup>TM</sup>t be a problem thanks to the metric system. 1000mbar = 1 bar and 1 bar = 14.5psi. There you have it.

So, can we all figure out what boost level in psi this car is requesting and making at 3000rpm?

RPM Requested Boost Actual Boost
2500……2100…..1800
2750……2200……1950
3000……2200……2250
3250……2200……2200
3500……2200……2100

The correct answer is…

The computer is requesting 1.2 bar of boost at 3000rpm. This can also be expressed as 17.4psi.

The turbo is boosting 1.25 bar of boost at 3000rpm. This can also be expressed as 18.1psi.

So why are the above numbers important to us other than acting as a boost guage to entertain us? Well, as you can imagine, if you had a boost leak you would have a car that is requesting the correct boost but you would see very little in the actual boost column. In the case that you had just installed your new little boost controller or N75 valve you could do some logging to find that your actual boost was far exceeding your computers' requested boost numbers causing your car to go into limp mode due to it's sensing an "overboost� condition. For those of us who dare to run a turbo that was not designed specifically for the software they are using, this is a great way to see why it is not working out for you. For example, the boost maps on a K03 will show the ECU requesting max boost at around 3000rpms (this is a small turbo that makes its boost low in the rpm range). Now if you were to throw on a Garrett gt28r or T28 turbo or even larger you would see that the computer will still request the max boost at 3000rpm, but the turbo is not capable of making it�TMs max boost until closer to 3800rpm leaving you with an �oeunderboost� condition.

NOTE: The sensor will only measure up to 2540mbar including atmospheric pressure. This means that if you are running more than 1.5bar or 21.75psi of boost this sensor will not measure beyond it. Both values will show maxed out at 2540mbar.[align=left] [/align]

 

I have a 98.5 and when I look at 115 it has N/A where the values should be.

 

99 or 99.5 and up can read it.

 

Jeez. I say 00+. Someone else says they can do it on a 97, and someone else says on 99+.

Does anyone know the real answer?

Also, fahquad. The article you posted was good. Except as far as measruing the atmospheric pressure, VAG will do that. Just look at what the mbar readings are at idle. Mine usually shows about 850 - i'm at elevation of 4,500 feet. If you're at sea level, it should show about 1,040 mbar at idle. Then you can subtract those numbers to get the true mbar.