Oscilloscope measurement of automobile intake pressure sensor signal and waveform analysis

The intake pressure sensor is the intake manifold pressure sensor. It is used in the D-type electronic fuel injection system (the L-type uses an air flow meter to detect the intake volume). The intake pressure sensor is generally installed behind the throttle valve and calculates the intake volume by detecting the pressure change behind the throttle valve. Its function is to detect the pressure change in the intake manifold and convert the intake pressure of the engine intake manifold into an electrical signal. Like the air flow meter, it is an important parameter for the engine control unit ECU to calculate the basic injection amount and determine the optimal ignition time.

Common intake air pressure sensors include analog, digital, and TMAP. Both analog and digital sensors have three wires: a power line, a ground line, and a signal line. Compared with the two, TMAP has an additional signal line for the temperature sensor.

The TMAP type intake manifold pressure sensor integrates a temperature sensor. The engine computer compares the intake temperature sensor and the boost temperature sensor. If the temperature difference is greater than 8 degrees Celsius, the coolant circulation pump will be turned on.

We use an oscilloscope to measure the analog intake pressure sensor signal of Mazda's 2007 2.3L displacement car.

Connect channel 1 of the oscilloscope to a BNC to banana cable, connect the black banana head to an alligator clip connected to the negative pole of the battery and grounded, and connect the red banana head to a piercing needle to the signal output end of the sensor.

The oscilloscope channel attenuation ratio is set to 1X, the vertical range is set to 500ms/div, and the time base is set to about 500ms. To avoid waveform burr interference, you can turn on the low-pass 30K for the oscilloscope, then quickly step on the accelerator, from idle speed to full throttle, and observe the waveform.

The signal voltage of the analog pressure sensor will change with the change of the engine vacuum. When idling, the throttle is close to vacuum, which means that the throttle is almost closed at this time. When the intake volume increases, the vacuum becomes smaller, the pressure becomes larger, and the waveform is upward. The principle is that the higher the absolute pressure in the intake manifold, the greater the deformation of the silicon diaphragm, and the deformation is proportional to the pressure. When the sensor structure and input voltage are constant, the higher the pressure acting on the circular silicon wafer, the higher the output voltage. Usually the output voltage of the intake pressure sensor is 1.25V at idle, slightly lower than 5V when the throttle is fully open, and close to 0V at full deceleration.

A digital intake pressure sensor, such as the one found on Ford engine control systems, will change its signal frequency (often a square wave signal) as the engine vacuum changes, but the voltage signal will remain constant regardless of how the engine vacuum changes.