3AE3 MT 2 — 3 Indirect Injection types

PRIORITY: What are the three gasoline indirect injection types?

Throttle-body injection (TBI), central point injection (CPI) and port fuel injection (PFI).

What makes gasoline injection “indirect”?

Fuel is injected outside the combustion chamber, into the intake airflow before entering the cylinder.

Where does throttle-body injection (TBI) deliver fuel?

Above the throttle plate, into a shared intake airflow path.

Where does port fuel injection (PFI) deliver fuel?

Into each cylinder’s intake port near the intake valve.

What is central point injection (CPI)?

A hybrid system that combines a central injector with tubes and poppet nozzles to distribute fuel to individual cylinders.

What components are in the six-cylinder CPI assembly described in the notes?

One central fuel injector, a pressure regulator and six poppet nozzle assemblies with nozzle tubes.

How does CPI combine features of TBI and PFI?

It uses central fuel metering like TBI but distributes fuel to individual intake ports more equally, like PFI.

How can you distinguish TBI, CPI and PFI in a diagram?

TBI: injector above throttle plate. CPI: central assembly with tubes to individual nozzles. PFI: separate injector at each intake port.

What are the main advantages of PFI?

More equal fuel distribution, tuned intake airflow, intake-valve cooling and cleaning, lower injection pressure than GDI and time for air and fuel to mix.

What controls fuel quantity when injector pressure is maintained?

Injector pulse width: how long the injector stays open.

Does the injector open farther to deliver more fuel in the lecture model?

No. It opens the same distance; a longer opening time delivers more fuel.

What is synchronized TBI?

Injector pulses are timed to distributor reference pulses.

What is non-synchronized TBI?

Injector pulses occur independently of distributor reference pulses.

What are the three PFI firing strategies?

Simultaneous double-fire, grouped double-fire and sequential injection.

What is simultaneous double-fire injection?

All injectors fire together once per crankshaft revolution.

What is grouped double-fire injection?

Injectors are divided into two groups that fire alternately.

What is sequential injection?

Individual injectors fire in sequence according to engine firing order.

How often does each cylinder receive fuel in sequential injection on a four-stroke engine?

Once every two crankshaft revolutions, timed near the intake event.

Which PFI firing strategy provides the most precise timing in the notes?

Sequential injection.

How does GDI differ from the three indirect injection types?

GDI injects directly into the combustion chamber rather than into the intake airflow.

What is stratified GDI operation?

The mixture is richer around the spark plug than in the rest of the cylinder.

What is homogeneous GDI operation?

The air–fuel mixture is approximately uniform throughout the cylinder.