1968 Shelby GT500

Barometric Pressure Sensor (BP)

The Barometric Pressure (BP) sensor operates as a piezoelectric (pressure-sensing) disc. However, rather than generating a voltage, its output is a frequency change. The sensor changes frequency relative to intake manifold vacuum. The sensor frequency increases as vacuum increases. The BP sensor is used to sense the changes in barometric pressure, allowing the PCM to sense the altitude at which the vehicle is operating. Its signal affects, spark advance for altitude compensation.
The BP sensor was only used in early MAF systems. Starting in 1994 Ford learned that air pressure can be calculated once the MAF sensor tells the computer the amount of air ingested by the engine.

Barometric Pressure Sensor

Altitude

Barometric Pressure

BP Frequency

Feet

 inHg

kPa

Hz

15000

16.9

57

120.4

14000

17.1

58

122.4

13000

18.3

62

125.5

12000

18.9

64

126.6

11000

19.5

66

128.7

10000

20.7

70

131.9

9000

21.0

72

138.1

8000

21.8

75

136.0

7000

23.0

78

138.3

6000

24.2

82

141.8

5000

25.0

84

144.0

4000

26.0

88

147.0

3000

26.6

91

150.0

2000

27.0

94

152.5

1000

28.9

98

156.1

0

29.92

100

159.0

-1000

31

103

162.4

29.92 inHg= Sea Level
100 kPa = Sea Level
5280 ft = 1 mile
14.7 PSI= Sea Level

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