MAP Sensor readings lower than mechanical Gauge readings??
#1
MAP Sensor readings lower than mechanical Gauge readings??
ok my 02' 6.0's MAP sensor is reading 10.9 hg on my scan tool ( kinda low ) but my mechanical gauge hooked up to the intake right next to the sensor is reading a pretty steady 19hg ( very healthy ) just in spec too... this was taken with a warm engine at idle.. is my misfire being caused by this ? any way i can test the map sensor with a multimeter before buying one new?
i think i may have found the true culprit of my lean sparkplugs and p0300 random miss ( pcm is misreading actual conditions and putting fuel in for the wrong conditions )
i think i may have found the true culprit of my lean sparkplugs and p0300 random miss ( pcm is misreading actual conditions and putting fuel in for the wrong conditions )
#2
TECH Senior Member
Your mechanical gauge is a vacuum gauge, it measures vacuum relative to BARO.
The MAP sensor measures absolute pressure (relative to absolute zero/void).
Vacuum is related to MAP as follows: VAC = BARO - MAP
BARO is appox 29.9 inHg at sea level
Your MAP is 10.9 inHg
VAC = 29.9 - 10.9 = 19 inHg which matches your vacuum gauge reading.
Or, if you prefer psi:
BARO = 14.7 psi
MAP = 5.4 psi
VAC = 14.7 - 5.4 = 9.3 psi = 19 inHg
Or, in Metric kPa:
BARP = 101 kPa
MAP = 37 kPa
VAC = 101 - 37 = 64 kPa = 9.3 psi = 19 inHg
The MAP sensor measures absolute pressure (relative to absolute zero/void).
Vacuum is related to MAP as follows: VAC = BARO - MAP
BARO is appox 29.9 inHg at sea level
Your MAP is 10.9 inHg
VAC = 29.9 - 10.9 = 19 inHg which matches your vacuum gauge reading.
Or, if you prefer psi:
BARO = 14.7 psi
MAP = 5.4 psi
VAC = 14.7 - 5.4 = 9.3 psi = 19 inHg
Or, in Metric kPa:
BARP = 101 kPa
MAP = 37 kPa
VAC = 101 - 37 = 64 kPa = 9.3 psi = 19 inHg
#3
TECH Senior Member
To test MAP sensor:
with scantool connected and showing MAP sensor, apply vacuum to MAP sensor directly (using handheld vacuum pump)...
for every 2 inHg on the vacuum pump's gauge, the scantool should show a 2 inHg drop on the MAP sensor...
i.e. if pump shows 10 inHg vacuum, then MAP should show 10 inHg less than BARO.
with scantool connected and showing MAP sensor, apply vacuum to MAP sensor directly (using handheld vacuum pump)...
for every 2 inHg on the vacuum pump's gauge, the scantool should show a 2 inHg drop on the MAP sensor...
i.e. if pump shows 10 inHg vacuum, then MAP should show 10 inHg less than BARO.