1968 Shelby GT500

Manifold Absolute Pressure Sensor (MAP)

To prevent the replacement of good components, be aware that the following non-EEC areas may be at fault:

*Unusually high/low barometric pressure.
*Kinked or obstructed vacuum lines (MAP).
*Basic engine (valves, vacuum leaks, timing, EGR valve, etc.).

The Manifold Absolute Pressure (MAP) 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 MAP sensor allows the PCM to determine what the engine load is. Its signal affects air/fuel ratio, ignition timing, EGR flow and altitude compensation.

Manifold Absolute Pressure Sensor

Manifold Vacuum

MAP Frequency

inHg kPa Hz
0 0.00 159
3 10.2 150
5 16.2 146
6 20.3 141
8 25.7 134
9 30.5 133
11 36.7 126
12 40.6 125
13 45.4 121
14 47.2 119
15 50.8 117
16 54.0 114
17 57.0 111
18 61.0 109
19 76.3 107
20 70.0 104
21 71.1 102
23 78.1 97
24 81.3 95
27 91.5 88
30 101.6 80

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

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