General description
MAP sensor (MAP) measures dilution in the intake manifold and its sensitive element converts the signal to electrical that can be returned to the onboard controller. MAP sensor is used mostly as a cheap alternative to sensors for engine load. Its relatively low cost is the reason for its wide distribution, though its measurements are not as accurate as the various types of sensors for the amount of air. MAP can be located in the engine compartment as a separate component or integrated in the onboard controller. MAP is used in both types of systems - MPi and SPi, but is more common in SPi.
Appearance
Fig. 1 shows a typical MAP sensor.
Fig. 1
Types of sensors
According to the principle of operation are:
Principle of operation of the MAP sensor
MAP is connected to the intake manifold through a vacuum hose. The vacuum in the intake manifold actuate the MAP sensor’s diaphragm. Converter transforms the measured pressure into an electrical signal which is fed into the onboard controller. ECU estimates the data from the MAP sensor values as: "Absolute Pressure" = "Atmospheric pressure" - "manifold pressure”.
By using the speed/density method, the onboard controller calculates the fuel mixture composition depending on the signal of MAP and engine speed. This method is based on the theory that with every turn the engine sucks fixed volume of air. Accuracy of this method can not be compared with that of the air quantity sensor, which after accurate measure of the airflow calculates the fuel mixture ratio based on mass or volume of air sucked in from the engine.
When there is a high level of vacuum in the intake manifold (e.g. idling), MAP output signal is relatively low and the onboard controller provides less fuel.
In systems with "wet" type intake manifold (e.g. SPi) changes in manifold pressure can cause the fuel entering the vacuum hose to reach the MAP. To avoid this, a special trap is used and accordingly traced vacuum hose. If the fuel reaches the MAP sensor, its diaphragm may be damaged.
In MPi systems the manifold is "dry" type and fuel can’t enter as it being sprayed over the intake valves. Therefore there is no risk of MAP sensor fuel penetration and contamination of the diaphragm, and therefore a special trap is not used.
When the MAP sensor is used as a separate component, inexpensive maintenance could be achieved. When MAP sensor is built into the onboard controller, possible replacement of the MAP will require the replacement of the whole controller.
Order to verify functionality of the MAP sensor
NOTE: If the MAP sensor is located inside the onboard controller, verification of the output signal is impossible.
1.) MAP SENSOR IN THE INTAKE MANIFOLD – ANALOG TYPE
-- Initial general inspection
-- Check the accuracy of the external MAP sensor
Terms under which checks are carried out - the engine not started and vacuum is provided with a vacuum pump.
Applied vacuum, mBar |
Voltage, V |
Value of МАР, Bar |
0 |
4.3 – 4.9 |
1.0 ± 0.1 |
200 |
3.2 |
0.8 |
400 |
2.2 |
0.6 |
500 |
1.2 – 2.0 |
0.5 |
600 |
1.0 |
0.4 |
Condition |
Voltage, V |
Value of МАР, Bar |
Vacuum, Bar |
Fully open throttle |
4.35 |
1.0 ± 0.1 |
0 |
Turn on ignition |
4.35 |
1.0 ± 0.1 |
0 |
Idling speed |
1.5 |
0.28 – 0.55 |
0.72 – 0.45 |
Stop engine |
1.0 |
0.20 – 0.25 |
0.80 – 0.75 |
Condition |
Voltage, V |
Value of МАР, Bar |
Vacuum, Bar |
Fully open throttle |
2.2 |
1.0 ± 0.1 |
0 |
Turn on ignition |
2.2 |
1.0 ± 0.1 |
0 |
Idling speed |
0.2 – 0.6 |
0.28 – 0.55 |
0.72 – 0.45 |
Applied voltage |
Voltage, V |
0.9 Bar (checking the pressure of the turbocharger |
4.75 |
Table 3
-- Fast verification of analog MAP sensor using an oscilloscope
Fig. 2
If voltage sharply rises to its maximum value when the accelerator is pressed, and quickly falls to the minimum when accelerator is released - MAP sensor is working properly.
-- Possible failures in the analog sensor:
Chaotic output signal
Missing of signal voltage
The MAP sensor power supply or signal is equal to the car battery voltage.
-- Other checks:
2.) MAP SENSOR IN THE INTAKE MANIFOLD – DIGITAL TYPE
NOTE: Real signal from the output of this type of MAP sensor can only be seen with the oscilloscope.
Fig. 3
200 mBar |
The speed must be reduced to 525 ± 120 rpm |
400 mBar |
The speed must be reduced to 1008 ± 120 rpm |
600 mBar |
The speed must be reduced to 1460 ± 120 rpm |
800 mBar |
The speed must be reduced to 1880 ± 120 rpm |
-- Possible failures in a digital sensor:
Lack of signal voltage
The MAP sensor reference voltage or signal is equal to the car battery voltage.
-- Other checks: