Fuel Injector: Description and Operation

Injectors
Each fuel injector (Fig 1) consists of a solenoid operated needle valve with the movable plunger rigidly attached to the nozzle needle. In the closed position, a helical compression spring holds the needle against the valve seat.

The injectors have a solenoid winding mounted in the rear section of the valve body, with a guide for the nozzle needle in the front section.

The injectors are operated in two stages, initially they are operated via a pull-in circuit, then when the injectors are open a change to a hold on circuit is made via current limiting resistors (Fig 2) for the remainder of the injection period as determined by the ECU in this way the heating effect on the output transistors of the ECU is reduced. It also ensures a rapid response from the injectors.

To open the injectors at the speeds required by the engine a fairly high current is needed. The ECU has an output stage to deliver this current, but to protect the output transistors of the ECU from injector faults a power resistor is wired in series with each three injectors. These resistors will limit current to a safe value, thus protecting the ECU. The power resistors (one for each group of injectors) are housed in a single unit to the right side of the engine valence by two screws.

The injectors are operated in two groups of six, which is further broken down into two sub-group of three, although each pair of sub-groups is operated simultaneously to make up the two groups.

A Bank B Bank
1A 3A 5A 1B 3B 5B
2A 4A 6A 2B 4B 6B