32
12. View reading on display.
DC Volts Type Sensor:
• Verify hand held vacuum pump is
at 0 in. of vacuum.
• Display reading should be approxi-
mately 3V or 5V depending on
MAP sensor manufacturer.
Frequency Type Sensor:
• Verify hand held vacuum pump is
at 0 in. of vacuum.
• Display reading should be approxi-
mately 4770RPM
±
5% for Ford
MAP sensors only.
• For other frequency type MAP sen-
sors refer to vehicle service manual
for MAP sensor specifications.
• It is O.K. if last two display digits
change slightly while vacuum is
held constant.
• Remember to multiply display
reading by 10 to get actual RPM.
• To convert RPM to Frequency or
vice versa, use equation below.
Frequency =
RPM
30
(Equation Only Valid for Multimeter
in 4 Cylinder RPM Position)
13. Operate Sensor.
• Slowly apply vacuum to MAP sen-
sor - Never exceed 20 in. of vacuum
because damage to MAP sensor
may result.
• Display reading should decrease
in voltage or RPM as vacuum to
MAP sensor is increased.
• Refer to vehicle service manual
for charts relating voltage and fre-
quency drop to increasing engine
vacuum.
• Use equation above for Frequency
and RPM conversions.
14. Test Results.
Good Sensor:
• S e n s o r o u t p u t v o l t a g e o r
frequency(RPM) are within manu-
facturers specifications at 0 in. of
vacuum.
• Sensor output voltage or frequency
(RPM) decrease with increasing
vacuum.
Bad Sensor:
• Sensor output voltage or frequency
(RPM) are not within manufactur-
ers specifications at 0 in. of
vacuum.
• Sensor output voltage or frequency
(RPM) do not change with increas-
ing vacuum.
Mass Air Flow (MAF)
Sensors
This sensor sends a signal to the com-
puter indicating the amount of air enter-
ing the engine. Depending on the sen-
sor design, the signal may be a dc volt-
age, low frequency, or high frequency
type. The CP7677 can only test the
dc
voltage
and
low frequency type
of
MAF sensors. The high frequency type
sensors output a frequency that is too
high for the CP7677 to measure. The
high frequency type MAF is a 3-pin sen-
sor used on 1989 and newer GM ve-
hicles. Refer to vehicle service manual
for the type of MAF sensor your vehicle
uses.
Test Procedure (see Fig. 35):
1. Insert BLACK test lead into COM
test lead jack.
2. I n s e r t R E D t e s t l e a d i n t o
test lead jack.
3. Connect BLACK test lead to good
vehicle ground.
4. Connect RED test lead to MAF
signal wire.
• Refer to vehicle service manual for
location of MAF signal wire.
• You may have to backprobe or
pierce MAF signal wire in order to
make connection.
• Refer to vehicle service manual for
best way to connect to MAF signal
wire.
5. Turn Ignition Key ON, but do not
start engine!
6. Turn multimeter rotary switch to...
