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MAP pressure

Date: Tue, 27 Jan 1998 06:51:03 +0000
From: "Douglas Hurst Quebbeman" <dougq@iglou.com>
Subject: Boost Guage Accuracy
The latest discussion is w.r.t Colin Hames' problem. Once again,
it's asserted that the guage is inaccurate. Ok. But where is the

The ECU measures the boost using the pressure transducer which
is mounted on the ECU analog board, right? And the ECU samples

this and then writes some value to the boost guage.

***  Signal conditioning converts the output to about 2.5 volts/bar. This output
is buffered and sent as an analog value to the boost display.

More likely, the design of the ECU code flow does not permit it
to update the display fast enough to reflect actual conditions
(i'm trying to avoi the use of the phrase "real-time" here).

****The "boost" guage has a slow sampling time.

Instead, what we need is a small smart box whose sole function
it is to monitor the MAP and update the display. As long as it's
signal-compatible, this could be a drop-in addition to most all of
the 5kt/200s. Sounds like a job for the might PIC processor!

Does anyone know of an ideal pressure transducer for this 
application? If not, I guess I'll have to dig out the latest DigKey
catalog and get to work...

*****  Bourns, Motorola, and a few other vendors made good cheap
MAP sensors. That and a cheap DPM  ( $15) will run you over $30
What's the problem with the OLD FASHIONED mechanical 30inch vacuum/
30PSI boost guage available from most performance shops, ( and JC Whitney etc)
for about $15-20 ( or cheaper sometimes... would wonder about the accuracy )