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4. Make sure that the sensor generates the correct frequency for a given RPM or airflow rate.
5. Use the Glitch Snare mode to detect dropouts or unstable output frequency.
• Reference Waveform
VEHICLE INFORMATIONS
YEAR
:
1990
MAKE : Buick
MODEL :
Le Sabre
ENGINE : 3.8 L
FUELSYS : Multiport Fuel Injection
PCM_PIN : Yel wire
STATUS : KOER (Key On Running)
RPM : 2500
ENG_TMP : Operating Temperature
VACUUM : 20 In. Hg
MILEAGE : 103128
NOTE
On some Digital Fast MAF sensors, such as the GM Hitachi sensor found on 3800
Buick V-6s, the upper left corner of the pulse is rounded off slightly. This is normal
and doesn’t indicate a bad sensor.
• Troubleshooting Tips
Possible defects to watch for are runted (shortened) pulses, unwanted spikes, and rounded off corners that could all
have the effect of garbling an electronic communication, causing a driveability or emissions problem. The sensor
should be replaced if it has intermittent faults.
Digital Karman-Vortex MAF (Mass Air Flow) Sensor
• Theory of Operation
Karman-Vortex type MAF sensors are usually manufactured as part of the air cleaner assembly. They are commonly
found on Mitsubishi engine systems.
While most
digi
t
al MAF sensors vary only their frequency with changes in
airflow rate, the Karman-Vortex type’s signal varies Pulse Width as well as Frequency with changes in airflow rate.
As the airflow increases, the frequency of the signal generated increases.
Karman-Vortex sensors differ from other digital MAF sensors during acceleration modes. During acceleration, not
only does the sensor’s frequency output increases, but also its pulse width changes.
6-29
Frequency stays constant when airflow is constant. Frequency increases as airflow
increases
f
rom snap
accelera
t
ion. Look for pulses that are a
full
5 V in amplitude
.
Voltage transitions should be straight and vertical. Voltage drop to ground should not
exceed 400 mV. If greater than 400 mV, look for a bad ground at the sensor or the
PCM.
FREQ = 6.57 kHz
MAX = 5.06 V
MIN = 0.00 V
•
Reference Waveform
VEHICLE INFORMATIONS
YEAR
:
1986
MAKE : Oldsmobile
MODEL : Toronado
ENGINE : 3.8 L
FUELSYS : Multiport Fuel Injection
PCM_PIN : B6 Yel wire
STATUS
:
KOER (Key On Running)
RPM : Snap Acceleration
ENG_TMP : Operating Temperature
VACUUM : 0-24 In. Hg
MILEAGE : 123686
• Troubleshooting Tips
Possible defects to watch for are runted (shortened) pulses, unwanted spikes, and rounded off corners that could all
have the effect of garbling an electronic communication, causing a driveability or emissions problem. The sensor
should be replaced if it has intermittent faults.
Digital Fast MAF (Mass Air Flow) Sensor
• Theory of Operation
Digital Fast type MAF sensors can be found on GM’s 3800 V-6 engine with the Hitachi sensor, Lexus models, and
many others. The Hitachi sensor has a square wave output in the 10 kHz range.
Voltage level of square waves should be consistent and frequency should change smoothly with engine load and
speed.
• Symptoms [OBD II DTC’s: P0100 ~ P0104]
Hesitation, stall, low power, idle problems, excessive fuel consumption, emissions failure
• Test Procedure
1.
Connect the CH A lead to the sensor output or HI and its ground lead to the sensor output LO or GND.
2. With the Key On, Engine Running (KOER), use the throttle to accelerate and decelerate the engine. Try different
RPM ranges while spending more time in the RPM ranges that correspond to the driveability problem.
3.
Make sure that the amplitude, frequency and shape are all consistent, repeatable, and accurate.
6-28
Frequency stays constant when airflow is cons
t
ant.
Frequency increases as air
f
low
increases from snap acceleration.
Look for pulses that are a full 5 V in amplitude. Voltage transitions should be straight
and vertical. Voltage drop to ground should not exceed 400 mV. If greater than 400
mV, look for a bad ground at the sensor or the PCM.
FREQ = 64.1 Hz
MAX = 4.93 V
MIN = 0.00 V
Frequency increases due to air
flow increase from snap accel.
Idle air flow here
before snap accel.