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 Vacuum		MAP Frequency
inHg	kPa	Hz
0	0	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

Article & images courtesy of fordfuelinjection.com.