MEFI Fuel Injection
8.1L MAP Circuit
The ECM sends a 5 volt reference voltage to the MAP sensor. This 5V feed is “watched” by the ECM’s A/D converter. If the voltage is too high or too low a “5V Reference out of range” fault code is set. The sensor responds to changes in the manifold pressure and returns a signal voltage (a portion of the supply voltage) on the signal wire. This signal will vary from about 1.0-1.5 volts at idle to about 4.0- 4.8 volts at WOT. The ECM sees this signal input through the A/D converter on the signal wire. Almost all inputs to the ECM that come in through an A/D converter can be seen by a scan tool. For the MAP sensor, this is “MAP Volts”. The 5V Reference voltage level is monitored by the ECM but can not be seen with a scan tool. There are 3 fault codes for the MAP sensor : “MAP Voltage High”, “MAP Voltage Low” and “5V Reference Out Of Range”. The “5V Reference Out Of Range” can be set by either the MAP or TPS as it is a shared circuit. If the MAP sensor fails, the ECM will substitute a default MAP value that will vary with RPM and set the appropriate fault code.
73
