D: Manifold Absolute Pressure (MAP) Sensor
Introduction
Introduction
1994 PCED OBDI-A | SECTION 18A: Diesel Diagnosis — 7.3L DI Engine |
D: Manifold Absolute Pressure (MAP) Sensor Introduction | D: Pinpoint Tests |
The MAP (manifold absolute pressure) sensor is a variable capacitance sensor that when supplied with a 5-volt reference signal from the PCM produces a digital frequency signal that indicates pressure.
Smoke Control — The MAP signal is used to control smoke by limiting fuel quantity during acceleration until a specified boost pressure is obtained.
Dynamic Injection Timing — Optimizes injection timing for boost pressure measured.
A MAP signal that is detected by the PCM to be out of range or at an incorrect value for specific conditions will cause the PCM to ignore the MAP signal and operate the engine from an inferred boost pressure signal).
After removing connectors always check for damaged pins, corrosion, loose terminals, etc.
| Test Points | Spec. | Actual | Comments |
|---|---|---|---|
| A to Grd | <5 ohms | Resistance to ground check w/key off, if greater than 5 ohms the harness is open. | |
| B to Grd | >5 ohms | Resistance less than 5 ohms indicates a short to ground. | |
| C to Grd | >5 ohms | Resistance less than 5 ohms indicates a short to ground. |
| Test Points | Spec. | Actual | Comments |
|---|---|---|---|
| A to Grd | 0-.25 volts | If greater than .25 volts signal wire is shorted to VREF or battery. | |
| B to Grd | 5 volts | VREF signal, should be 5 volts ± 0.5. | |
| C to Grd | 5 volts ± .5 | Signal line is pulled up to 5 volts ± 0.5 volts when disconnected from sensor. |
| Test Points | Spec. | Actual | Comments |
|---|---|---|---|
| No. 91 to A | <5 ohms | Resistance from sensor connector to 104 pin connector. | |
| No. 90 to B | <5 ohms | Resistance from sensor connector to 104 pin connector. | |
| No. 34 to C | <5 ohms | Resistance from sensor connector to 104 pin connector. |
| Test Points (+) No. 34 to (-) No. 91 | Operational Signal Checks (Check with breakout box installed in line with the PCM) | |||
|---|---|---|---|---|
| Frequency | PSI | KPA | Actual | Comments |
| 106-114 | 14.7 | 101 | Frequency with key on engine off, atmospheric pressure, changes with altitude and barometric pressure. | |
| Voltage | N/A | N/A | Average voltage value of 0 to 5-volt square wave signal. | |
126 = Signal frequency was greater than 270 or less than 80 hz for more than .10 seconds.
127 = MAP in-range concern (inactive for .25 seconds)
128 = Detected high boost signal at low idle (restricted MAP sensor inlet)
| Frequency (Hz) | Pressure kPa (psi) | Frequency (Hz) | Pressure kPa (psi) |
|---|---|---|---|
| 17 | 75 (11.0) | 127 | 129 (19.0) |
| 27 | 79 (7.0) | 137 | 134 (19.5) |
| 37 | 83 (12.0) | 147 | 140 (20.0) |
| 47 | 88 (13.0) | 157 | 146 (21.0) |
| 57 | 93 (13.5) | 167 | 153 (22.0) |
| 67 | 97 (14.0) | 177 | 160 (23.0) |
| 77 | 102 (15.0) | 187 | 166 (24.0) |
| 87 | 107 (15.5) | 197 | 173 (25.0) |
| 97 | 112 (16.0) | 207 | 180 (26.0) |
| 107 | 117 (17.0) | 217 | 187 (27.0) |
| 117 | 123 (18.0) | 227 | 189 (27.5) |
| D: Pinpoint Tests |