Mass air flow (maf) sensors, Frequency = rpm 30 – Actron AutoTroubleShooter CP7677 User Manual

Page 32

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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...

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