AEM 30-1931 Universal Fuel Ignition Controller 8 Channel User Manual
Page 12
Page 12
When talking pressure, there are two common ways pressure is represented,
Gauge, and Absolute, Gauge being by far the more common way. Take a tire for
example, if the measuring gauge says 50 psi, we say the tire has 50 psi of air in it.
However, that is not 100% correct. The tire actually has air at 50 psi above atmospheric
pressure, which is known as psi gauge (psig). The total pressure, or absolute pressure
(psia) is actually 50 psi on the gauge plus the atmospheric pressure. So, the absolute
pressure is the gauge pressure plus the atmospheric pressure. What about boost
gauges? Most boost gauges display gauge pressure both above and below
atmospheric pressure. Pressure above atmospheric pressure is commonly referred to
as ”Boost” pressure. Pressure below atmospheric is commonly referred to as
“Vacuum”. So why the lesson on absolute pressure? BECAUSE THE F/IC READS
AND DISPLAYS ABSOLUTE PRESSURE!!! For easy reference, the following
formulas can be used to determine, “Boost” and “Vacuum’ pressures. Atmospheric
pressure can be determined by reading the F/IC pressure with the key on and the
engine off.
P
(boost)
= P
(F/IC)
–
P
(atmospheric)
P
(vacuum)
= P
(atmospheric)
– P
(F/IC)
Now that you’re starting to grasp absolute pressure, you might wonder why the F/IC
reads absolute pressure. Well, absolute pressure is the only accurate, repeatable way
to measure manifold pressure. Measuring only “Boost” pressure does not account for
changes in atmospheric pressure. Changes in atmospheric pressure will cause
changes in manifold pressure. For example, let’s consider a boost gauge at high
elevation, where atmospheric pressure is 12.7 psia. A boost gauge reading of 10 psi
will give an absolute pressure of 22.7 psia (12.7 + 10). Now, take the same boost
gauge at sea level, where atmospheric pressure is 14.7 psia. A boost gauge reading of
10 psi now gives an absolute pressure of 24.7 psia (10 + 14.7). The boost gauge
displayed 10 psi boost in both locations, however, the absolute pressure was two psi
greater at sea level. By measuring absolute pressure, instead of gauge pressure, the
F/IC can be tuned correctly for all operating conditions.
Loading the FIC software
Insert the supplied software disk into your CD drive. The disk should
automatically load. To manually load the software, double click the file
“FIC8Releasexxxxxx.exe”. Follow the on-screen dialogue to finish the install. Load the
USB drivers by double click
ing on the file “CDM x.xx.xx.exe” (C:\Program
Files\AEM\FIC). Latest software versions can be found on the Electronics Forums at
Opening a Calibration
(Note: Changes made to FIC calibrations are made real-time and are autosaved
on the calibration that is currently open. If you do not want to modify a file, it is
recommended that you save the file under a different name using the “Save As”
function.) Start the FIC software by double clicking on the
“AEM FIC” icon on your
desktop. Go to File>Open and locate the file
“Base Cal.fi8”. If the default file locations
were used to load the software, the
“Base Cal.fi8” file should be found in the FIC folder
C:\Program files\AEM\FIC\. See Figure 21.