Fuel Injection Comparisons

Fuel injectors are activated by the engine control module either individually, in groups or all at once (during starting):

- All at once = Parallel Fuel Injection
- In groups = Semi Sequential Fuel Injection
- Individually = Full Sequential Fuel Injection

PARALLEL INJECTION

Parallel injection refers to simultaneous activation of all fuel injectors and takes place only when the cylinder reference point sensor (pulse generator) has supplied no signal since starting the engine.












As soon as a signal is applied, the system switches over to semi-sequential injection after the next deceleration phase.

Each injector valve group is activated by one output stage (power transistor). This arrangement makes it possible divide the injection cycle into cylinder groups (semi-sequential injection)

SEMI-SEQUENTIAL INJECTION







At an engine speed of 600 RPM, fuel is injected once per 720 degrees of crankshaft rotation into one cylinder group.

This facilitates precise metering of the quantity of fuel since the injector valve are not activated as often. It also enables limited engine operation in the even of failure of one group.

Semi-sequential injection is only active when the ECM has received the cylinder ID signal during start-up. If the signal is not received after the engine is already running, the system remains in semi-sequential injection.

FULLY - SEQUENTIAL INJECTION
Starting with the M3.x versions there is a separate final stage output transistor, in the Control Module, for each injector. Fuel is injected into the incoming air charge just prior to the intake valve opening. Power is supplied to all injectors from the main relay, and each injector is activated by its own final stage.












Programming
The Control Module is programmed to activate the injectors once for every two revolutions of the crankshaft.

Triggering is first established from the input signal of the speed/reference sensor.

The signal from the cylinder ID sensor ensures that the injection charge is timed to the proper cylinder. When activated, each injector delivers the full amount of fuel required for each working cycle.

Loss of the cylinder ID sensor will only affect the full-sequential injection to the point that the injected charge of fuel may not be timed to each respective intake valve.