So I just got my ScanGauge today, and after digging a little, I thought perhaps the XGauge feature could be used to calculate approximate boost vs. the Manifold Absolute Pressure that's available as a standard gauge with it. I posted in another thread and emailed Linear Logic probing for the method to do it. Then I found THIS POST on the TDIClub forum - exactly what I was looking for - and it WORKS!

Atmospheric pressure starts at 14.7psi at sea level, and drops approx. 0.5psi per 1000 feet of elevation...

For 14.3PSI atmospheric pressure (about 800 ft elevation):
TXD: 68 6A F1 01 0B
RXF: 04 41 85 0B 00 00
RXD: 28 08
MTH: 00 91 00 64 FF 71
(note - you don't enter the spaces - they're just to make it reading-friendly)

For other pressures, just substitute the following for the last four characters of the MTH string (replace the FF 71):
12.0 -- FF88
12.1 -- FF87
12.2 -- FF86
12.3 -- FF85
12.4 -- FF84
12.5 -- FF83
12.6 -- FF82
12.7 -- FF81
12.8 -- FF80
12.9 -- FF7F
13.0 -- FF7E
13.1 -- FF7D
13.2 -- FF7C
13.3 -- FF7B
13.4 -- FF7A
13.5 -- FF79
13.6 -- FF78
13.7 -- FF77
13.8 -- FF76
13.9 -- FF75
14.0 -- FF74
14.1 -- FF73
14.2 -- FF72
14.3 -- FF71
14.4 -- FF70
14.5 -- FF6F
14.6 -- FF6E
14.7 -- FF6D
14.8 -- FF6C
14.9 -- FF6B
15.0 -- FF6A

Huge kudos for seftonm over there for finding other smart guys and working this out!

UPDATE:
Thanks to Tu13es for being persistent - the Linear Logic guys came up with a solution for the R55/R56/R57 issue that required MAP to be displayed also.

On the R56 - use TXD of 07DF010B instead!

 

Stupid question, are the spaces in the code just for ease of reading?
I am just learning how to use this function so I want to make sure.
I did not see any code with spaces from what I remember.
Thanks

 

Did you miss the part that said:
???

 

Yes

 

Cool feature, I really need to get one of these.
And to help figure out your elevation (without installing an Altimeter in your car: http://www.worldatlas.com/aatlas/infopage/elvation.htm

 

Got mine working today. It was -.2 off from the MAP reading entered. My MAP always reads 14.1 at the key on position. I had to enter the 13.9 value to get 0.0 boost while my MAP read 14.1; looking at both at the same time.

 

Edit - OK - I see what you mean - it's "close"... but there's definitely something a little funny happening with the math (and, I think, with the reading of MAP in general)... I too get -.2PSI with the engine off and would expect this to be 0 (normal barometric pressure at my location)... but MAP actually looks like it might be reading a tiny bit HIGHER than what I would calculate my pressure to be at my elevation... odd...

 

Would this work for an R56 Mini? I tried it but can't seem to get it to display anything

 

Should work fine...the info Blimey got was from a Volkswagen forum...

 

Perhaps theres a difference in the ECU outputs of an r53 vs r56? If so I wonder if the program for the Scangauge would need to be altered

 

Did you take the 'spaces' out?

I don't see how it would be any different in the R56. The other pre-programmed functions work across the board on all OBD-II vehicles.

...just occurred to me while typing this...would the R56 have a MAF sensor instead of a MAP sensor like the R53 has? Could this make a difference in the 'programmed' MAP reading?

 

Also - there *might* be a difference in how you'd program this for CAN vs. non-CAN... just guessing...

Does the "HP" programming available on the ScanGauge site work for you?

 

I got it all figured out now, I had to display MAP and the new program at the same time for it to work, I'll try the HP today

 

eh? I don't display MAP and BST at the same time (usually) and mine works... hmmm.

 

If your altitude varies, can this still be used? How accurate would it be? I live about 250 above sea level. But frequently drive over mountains as high as 3000 feet, and on longer trips, up to 10,000 feet. If I set it to my "home" elevation, don't I have to reset it at every elevation to see an accurate reading?

I don't think I under stand the benefit of doing this unless you drive in a fairly flat region.

 

Well, that depends entirely on (a) how accurate is "good enough" for you and (b) how much elevation change you go through regularly... As it says in the first post, atmospheric pressure drops approximately 0.5psi per 1000 feet of elevation...

I spend most of my time around 500ft. But occasionally get up to 6000ft. In those cases, if I REALLY want to know my boost, I can do the math in my head...

The ScanGaugeII really ISN'T the solution for someone who wants to see accurate boost vs. atmospheric, all the time, in any conditions. But if you occasionally want to see boost, or you're happy with approximate boost most of the time, it works fine. Given that very few folks actually NEED to know what their boost is, the estimates are pretty useful and interesting for many of us.

 

I set mine up for my elevation which should have been 14.3 or 14.4 I'm at about 700 feet. With that I was getting a negative .6 at key on. I fiddled with it and set it at 14.0 and now I've got this reading...

MAP 14.1
BST 0.00

When I'm at idle I get
MAP 6.1
BST -8.0

I see a lot of negative numbers on the BST when I rev 'er up. Is that right? I've never had a boost gauge, so this is kinda new to me.
Thanks for the help.

 

Yeah... there's some funky reporting of MAP at key-on... not sure why that is... it MAY be normal... I don't know...

But YES... You'll see LOTS of negative numbers... that's vacuum, and that's what your car runs under most of the time (cylinders sucking air in, vs. supercharger "blowing" air in)...

 

Thanks Blimey. I'll keep fiddling with it.
Any other Xgauges that work with the Mini? I like to see speed, intake temp and water temp. Volts were great to determine if my battery is staying on par. Great gauge overall. Probably the best $149 I've spent for a mod.

 

It only works for me on the R56 if I'm also displaying the MAP gauge. Obviously, this is a less-than-optimal choice :-)

I tried converting the gauge into CAN addressing format, but it didn't fix the issue.

The CAN version of this xgauge just requires a change to the TXD line.

Non-CAN TXD: 68 6A F1 01 0B
CAN TXD: 07 E8 02 01 0B

I was also hoping that using the CAN version would make them refresh faster than using the non-CAN version, which I assume has to be translated. Of course, this is all just a SWAG on my part.

Does anyone know why it needs to have MAP displayed for boost to display?

 

Not a clue... doesn't make ANY sense to me why it would matter whether you're displaying MAP or not... and why it works correctly on the 1st gen (and entirely different makes and models of cars), but not on the 2nd...

 

That seems odd that you'd need to have MAP up at the same time as BST.
I've been diving around the last couple days with my new BST gauge and it's not all that it's cracked up to be. It's ok, but i question that i have it set up right. I see negative numbers most of the time, then when I boot it I get up to about 8.5. It's slow to catch up, and is usually reading peak when I'm hitting the next gear.
Oh well, it's really more eye candy than techie isn't it.

 

Nope, you've got it set up right. A lot of the time the car will be showing negative boost, since there's a vacumn as the air is sucked into the engine. When you hit the point where air is being forced into the engine (via supercharger or turbocharger), the value will go positive.

I don't think the ScanGauge can read the OBD values from the R53 as fast as it can from the R56 (ISO vs. CAN rates), but with CAN you need to set the ScanGuage speed to FAST to take advantage of it.

I logged a support ticket with Linear-Logic to see about the BST/MAP issue, but haven't heard anything back yet.

 

Hmmm... yeah, update speed may be your primary problem... mine works fine and reports boost at the point that I'd expect - peaks at about 14.5psi with a 15% pulley...

 

Agreed on the update speed. The SG II is delivered with a 2 second update rate. You can change it for a more rapid update rate.