Re: Boost Guage Accuracy

[Orin Eman <orin@wolfenet.com>]

> 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.

Nope, the pressure transducer signal goes thru an op-amp buffer to
the dash guage.  It is the guage itself that is inaccurate.

> So, are we looking at sampling error? I hope not, if so, then the
> ECU is making bad decisions about boost.

Fortunately, the ECU functions see the correct boost signal, unless
the sensor itself gets toasted.

> 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!

Hmmm.  I could modify my duty cycle meter for this... use a 16C71
instead of a 16C84... change the input circuit slightly.  Cost with
a remote mount 2 digit LED display would be $30 to $35.
(I have a PIC based duty cycle meter available to list members
essentially at cost - the display fits in a suitably modified
5k dash switch blank.)

Or you could get a cheap LCD panel meter and connect it to the ECU
output signal that goes to the boost guage.  A voltage divider
would be required to scale the signal.

> 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...

Unobtanium.  It's the Motorola MPX4250ASX - try Allied or Newark
electronics, maybe they have some now.

Orin.