[200q20v] bar: from .1 to 1.8...is this normal?

[Calvin & Diana Craig]

I see this comment about the boost gauge being useless after a chip change
quite frequently.  Given the inherent inaccuracies of the digital gauge in
the first place, the "usefulness" of the gauge doesn't change with a change
in the pressure sensor.  The pressure sensor (motorola variety) just sends
out a 0 to Vcc signal in relation to MAP.  The stock sensor is 0 to 2.0 bar,
usually the ones that are insterted with a chip are 2.5 Bar. If you multiply
the reading on your digital display by 1.25 (2.5/2.0), it should be right
on, hence 1.8 * 1.25 would be approximately 2.25 bar. This is exactly what
Scott Mockry measured on the graph of the 1991 Wagon's boost vs. RPM with
the modified ECU.  On the low end, the 0.1 bar is probably a little off.  I
don't know what the reason is behind this but both 200's that I have develop
this problem sometimes where the boost gauge likes to read too low for a
little while.  I do see .2 occasionally when it's working properly, but I am
at 5k to 6k feet (stock ECU).
--Calvin



Assuming that stage 3 means that the pressure sensor has been
upgraded, your dash boost gauge is now almost meaningless. Surely you
expect that your maximum boost is actually above 1.8 bar, right? Best
advice: install an analogue boost gauge. Quick, cheap and easy to
do--except deciding on a spot to install the gauge. Mine's in the
glove box.

Phil