Fuel Delivery and Air Induction: Description and Operation

FUEL DELIVERY

NOTE: The natural gas fuel system is a returnless fuel system.

The sequential multiport fuel injection (SFI) provides the fuel/air mixture needed. The induction system is mounted on an aluminum intake manifold. Fuel flow is as follows:
1. Fuel is supplied from the vehicle's four high-pressure fuel tanks through a solenoid valve mounted on each fuel tank.
2. It is then filtered in the coalesce/filter assembly and sent to the fuel pressure regulator.
3. The fuel is then sent to the fuel injection supply manifold.
4. A fuel pressure regulator mounted to the vehicle frame controls the fuel delivery pressure at a constant 759 kPa (110 psi).


Fuel Injectors
The eight fuel injectors are:
- Positioned so that their tips direct fuel just ahead of the engine intake valves.
- Connected in parallel with the fuel pressure regulator.

Fuel Injection Timing
For fuel injection timing:
- Each fuel injector is energized once every other crankshaft revolution in sequence with ignition firing order.
- The period of time that the fuel injectors are energized (injector on time" or pulse width) is controlled by the Powertrain Control Module (PCM).
- Air entering the engine is monitored by flow, pressure and temperature sensors.
- The signals of the electronic engine control sensors are processed by the PCM.
- The PCM determines the needed injector pulse width and sends a command to the fuel injectors to meter the exact quantity of fuel.
- On natural gas vehicles, a fuel injector driver module energizes the fuel injectors.
- For natural gas engines, fuel entering the fuel injection supply manifold is monitored by:
+ a fuel pressure sensor and
+ 2 fuel temperature sensors.

AIR INDUCTION
Components
All engines are equipped with:
- Replaceable dry-type Air Cleaner Element (ACL).
- Engine air tray, is attached to the RH front fender apron.
- Mass Air Flow (MAF) sensor.

Operation
The air induction system supplies clean air to the throttle body. It operates as follows:
1. Outside air enters from an opening in the LH front fender apron into the engine air cleaner where it is filtered by the air cleaner element.
2. This filtered air then travels through the mass air flow sensor, air cleaner outlet tube and into the throttle body.
3. The Positive Crankcase Ventilation (PCV) system is also supplied clean air through a fitting on the air cleaner outlet tube.