Megasquirt Advice and discussion.

[Max777]

Well, I know that the trap door sensor is a bit different from a "hot wire" style MAF, and that this is used for fuel on the stock ECU. I also know that the pressure sensor looks at boost/ vaccum and these parameters affect the timing on the RX-7... so what's different between a pressure sensor and a MAP sensor? I thought that these were the same thing, no? And if you cant have both, then why does this car have both systems?

I mean, a "pressure sensor" is fundamentaly the same thing as a MAP sensor, they both sense pressure, or am I totally missing something?

[RETed]

Originally Posted by Max777

Well, I know that the trap door sensor is a bit different from a "hot wire" style MAF, and that this is used for fuel on the stock ECU.

Yes, two different ways of doing this same thing.
They both measure "mass air", or the amount of air flowing into the intake / engine.

so what's different between a pressure sensor and a MAP sensor? I thought that these were the same thing, no? And if you cant have both, then why does this car have both systems?

Good question...
IN GENERAL:
A "pressure sensor" can only see pressure or positive pressure relative to "0 atmospheric (pressure).
A "MAP sensor" (remember, "MAP" stands for "manifold absolute pressure") senses both pressure *and* vacuum.
The "absolute" part means it ignores "relative to 0 atmospheric (pressure)".
What this means is that MAP sensors start at "absolute vacuum" or very near that level - this is it's zero point.
(Absolute vacuum is considered 30.0inHg or "-14.7psi" - most people don't like seeing "-" and "psi", but it's easier to explain this way.)
At sea level or "0 atmospheric pressure", a MAP sensor will actually "see" ~14.7psi.
http://wiki.xtronics.com/index.php/P...nversion_Table

Now, in the FC's case, Mazda does call the non-turbo FC's pressure sensor a...well, "pressure sensor".
The turbo FC's pressure sensor is called a "boost sensor".
That just confuses the whole issue. :P
This the learned, the non-turbo FC pressure sensor is actually a "1-bar MAP sensor" (reads vacuum up to "0" atmosphere); the turbo FC pressure is actually a "2-bar MAP sensor" (reads vacuum up to ~15psi of boost).

I mean, a "pressure sensor" is fundamentaly the same thing as a MAP sensor, they both sense pressure, or am I totally missing something?

Yes, in a sense.
I hope the above clears things up.


-Ted