Bosch FIX 7677 Mode D'emploi page 33

Fig. 35
Frequency
Only
Ground
Black
Red
sensors.
• 4 Cylinder RPM position for Low
Frequency type MAF sensors.
7. View reading on display.
DC Volts Type Sensor:
• Display reading should be approxi-
mately 1V or less depending on
MAF sensor manufacturer.
Low Frequency Type Sensor:
• Display reading should be approxi-
mately 330RPM ± 5% for GM Low
Frequency MAF sensors .
• For other Low Frequency type MAF
sensors refer to vehicle service
manual for MAF sensor specifications.
• It is O.K. if last two display digits
change slightly while Key is ON.
• Remember to multiply display read-
ing by 10 to get actual RPM.
• To convert RPM to Frequency or
vice versa, use equation below.
Frequency =
{Equation Only Valid for Multim-
eter in 4 Cylinder RPM Position}
DC
Only
Typical GM 1988 & older
Low Frequency type
MAF Sensor
RPM
30
8. Operate Sensor.
• Start engine and let idle.
• Display reading should...
- increase in voltage from
Key On Engine OFF for DC
type MAF sensors.
- increase in RPM from Key
On Engine OFF for Low Fre-
quency type MAF sensors.
• Rev Engine.
• Display reading should...
- increase in voltage from Idle
for DC type MAF sensors.
- increase in RPM from Idle
for Low Frequency type MAF
sensors.
• Refer to vehicle service
manual for charts relating
MAF sensor voltage or fre-
quency (RPM) to increasing
air flow.
• Use equation above for Fre-
q u e n c y
conversions.
9. Test Results.
Good Sensor:
• Sensor output voltage or frequency
(RPM) are within manufacturers
specifications at Key ON Engine
OFF.
• Sensor output voltage or frequency
(RPM) increase with increasing air
flow.
Bad Sensor:
• Sensor output voltage or frequency
(RPM) are not within manufactur-
ers specifications at Key ON En-
gine OFF.
• Sensor output voltage or frequency
(RPM) do not change with increas-
ing air flow.
10. Maintenance
Periodically wipe the case with a
damp cloth and mild detergent, Do
not use abrasives or solvents.
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