GxT Ferret 92 Color Labscope - Manual (Page 23)

23 www.gxtauto.com
that the equalization only took about 80 mS to occur, so engine speed hasn’t increased much since the throttle
was snapped open. Because the resistance of the throttle plate has been removed, the intake pulsation is more
pronounced as engine speed is still low. Over the next 1 second you can see that air mass increases as engine
speed increases.
The next rapid drop in voltage indicates that the throttle was released and airfl ow decreased dramatically as high
vacuum replaced nearly atmospheric pressure in the manifold. The remainder of the trace shows air mass decreasing
as the engine returns to idle. This test is used to determine if the MAF is capable of sensing maximum air fl ow. If
it can’t, either the hot wire is contaminated or the sensor is bad. Over 3.8 volts maximum is what we want to see
here. This MAF looks good with a peak voltage of almost 4 volts and a very quick response at the initial throttle
opening. Idle voltage is normally about .6 volts with the engine at operating temperature.
Fuel Pump:
Fig. 19 is a current waveform of an electric fuel pump. On a good pump
average amperage will be within specifi cations, the humps will be fairly
even and peak to peak amperage will be between 15% and 25% of
the average amperage. Pump speed in RPMs can be determined by
using time cursors to measure the time it takes for one revolution in
milliseconds and then multiplying by 60,000. In most cases that will
mean placing the cursors so that there are 8 humps between them.
Most pumps have 8 commutators.
Amperage specifi cations are not published in most information
systems, but you can fi nd them in the Ferret 601 SmartSpec CD. Too
many variables affect pump speed to publish anything other than broad
specifi cations, so only failure speeds are published. Amperage and
pump speed will very greatly from system to system and aftermarket
pumps will often be quite different than OEM pumps.
Most bad pumps will have one or more very uneven peaks and/or valleys in the waveform and peak to peak amps
will be out of the 15% to 25% range when compared to average amperage. Excessively high or low amperage also
points to a bad pump or a circuit problem in the case of low amperage.
When current ramping pumps that draw more than about 5 amps it is advisable to use AC coupling and a Voltage
Scale that equates to a scale of 5 amp or less in order to see the ripple in detail. DC coupling and a higher range
will be necessary to see average amperage.
Using the USB Thumb Drive to Capture Screen Shots
Connect the USB Adapter Cable to the back of the 92. It may be necessary to remove a protective
plug to gain access to the adapter port. Attach the included Thumb Drive to the adapter cable.
You may attach the thumb drive anytime before you need to press the reference button.
Press the Hold Button to freeze the screen. Press the reference button. After 5 seconds you will
hear a beep indicating the screen shot has been copied to the thumb drive.
Remove the Thumb drive from the 92 and connect it to a Windows XP or Macintosh Computer.
Once the Thumb Drive mounts on the computer, open the drive. The fi les will be numbered F91-NN. NN is a
sequential number assigned by the 92. You may save 99 screen shots before the 92 will start over at 01. If another
fi le ending in 01 is present on the Thumb Drive it will be overwritten.
The fi les may be copied to your computers hard drive and viewed or editied using any program capabile of opening
a PNG File.