Using MAP Sensing for Engine Phase Detection

Using MAP Sensing for Engine Phase Detection

A technique often found on superbike engines, but less common in road cars, is using a Manifold Absolute Pressure (MAP) sensor to determine engine phase. This approach is only possible when running individual throttle bodies (ITBs).

Last year, we partnered with Jenvey Dynamics and SNG Barratt to develop a bolt-on fuel injection kit for the Jaguar E-Type straight-six engine. To maximise both fuel efficiency and throttle response, sequential injection was essential. However, since the kit had to remain simple to install, adding a traditional cam sensor was not an option.
You can read more about that kit on the SNG Barratt website.

How MAP-Based Phase Detection Works

By fitting a pressure take-off behind the butterfly on one runner and connecting it to a MAP sensor, the ECU can detect the pressure drop when the inlet valve is open and the piston is moving down, drawing in air. The ECU samples MAP data once per crank tooth, making it possible to see the pressure wave inside the ITB runner.

The diagram below shows one complete engine cycle for a cylinder, based on a 36-tooth crank trigger. Since an engine cycle spans two crank rotations, the ECU must evaluate 72 teeth to capture the full cycle.

  • The dip on the left of the trace represents the vacuum created as the piston moves downward with the inlet valve open.
  • At idle, this dip reaches around 40 kPa near crank tooth 15.
  • On the following crank rotation, when the inlet valve is closed, the MAP reading rises to around 90 kPa.

This difference makes it straightforward for the ECU to determine engine phase:

  1. The ECU samples MAP at crank tooth 15 on each rotation.
  2. If the readings differ by more than ~25 kPa, phase can be determined reliably.
  3. A negative difference indicates the compression phase; a positive difference indicates the exhaust phase.

Real-Time Example

The GIF below demonstrates this in practice:

  • The engine begins at idle,
  • transitions to part throttle,
  • responds to a throttle blip,
  • and then returns to idle.

IMAP Sync Setup on a T Series ECU

This functionality is available on all T Series ECUs.
A MAP sensor connected to the inlet manifold is called an IMAP sensor, to differentiate from a sensor connected to the exhaust manifold, which is an EMAP sensor.

To set this up, either a second MAP sensor must be fitted, or a single MAP sensor can be used.
If a single MAP sensor is used, then it cannot be used for barometric corrections while the engine is running. The MAP value is read with the engine off to store the current barometric pressure, and then it is no longer used for barometric pressure readings.
Once the engine is started, it is used for engine sync only.

If two sensors are used, one is used for sync and the second is used for barometric pressure corrections.

These are set in the ECU Inputs section.

On the dyno, we only used one sensor.

In the Sensor Configuration, configure the sensor.

In the Engine Configuration, set the Cam 1 Profile to Use IMAP Sync, and the Engine Phase at Sync to Compression.
This enables the IMAP Cam Sync Options section.
Calculate the correct tooth and IMAP difference, and enter these values.
As can be seen in the live data above, the dip can move with RPM. Set upper and lower RPM limits so that the phase is found correctly.

That's it.
If everything has been installed and configured correctly, the ECU will now be able to detect the correct engine phase, and be able to use sequential injection.