NefMoto

Audi TT Mk1 (2001) AMU engine. (Also playing with same thing on an AMB engine A4). I have the KWP1281 protocol 'down' - i.e. I can link and read / write.

I am reading the 'boost' pressure - using the pressure sensor above the intercooler -  seems to be the closest thing to a boost pressure measurement. At least I believe that is the sensor I am reading - 3?4? wire pressure sensor. Yes - fyi I pulled the connector and the reading maxed.
I am reading group 115(4) on this (which seems to be the same as 118(4), 119(4), 204(4), 206(4),and found a pile more.

In any event, the group 4 readings are static for byte 12 ( 0x1B), static for byte 13 (0x4B),  dynamic seeming to be scaled to pressure on byte 14, with a range from ~0x74 through 0xAD for the AMU / TT and 0x70 through 0xA2 for the AMB / A4.

Using my mech vac gauge, at 0x76 reading byte 14 I am at ~5inHg ref to Atm, or about 0.8bar absolute. Max boost on the K04 is about 8lbs, at least on this engine, or ~ 1.5bar Watching the numbers jump around, it seems to track ok, with about 117=0.8bar, 173 = 1.5bar, so about 56/.7 ratio of byte 14 to bar, or 80 to the bar.

Reading through Tony's post with the 'KWP1281 Measuring Block Value Formulas.txt' and trying everything that seems to be pressure does not match up. Also reading through ISO14230 / ISO15031 trying to get a hint as to the scaling and not having much luck. I am doing it empirically, would prefer the 'real' number.

Question - what is the scaling factor for these, and is the -0x1B significant to this conversion (since not all of the memory locations have a 0x1B, and I thought this was 'data type').
Q2 - is there a table that matches these older Bosch Motronic units?
Q3 - Should I be able to link to this ECU with KWP2000 / ISO14230 protocol? (cus I cant get it to work)

Thanks!

well nothing to do but a decomp on the micro to figure it out. I purchased one of these sensors and am creating a voltage/pressure graph and will go looking for the scaling routine in the code.