Electronic fuel injection

ELECTRONIC FUEL INJECTION

Introduction

• Strict emission standards require precise fuel delivery

• Computers used to calculate fuel needs

• EFI very precise, reliable & cost effective

• EFI provide correct A/F ratio for all loads, speeds, & temp ranges

The Fuel Injector

• Electromechanical device• Controlled by PCM• Engine rpm determines when injector

opens• How long it stays open determined by:

– Engine temp– Engine load– Throttle pos.– O2 sensor voltage

Throttle Body Injection (TBI)• First injection

unit used• Housing similar

to Carb• One or two

injector• One or two of

these units mounted to intake manifold

FIG 6-40 CLASS

LOW PRESSURE FUEL INJECTOR

• 13-16 psi operating pressure

• Ball style pintle

• Easily replaceable

GM’s Crossfire Injection

Multi-Port Fuel Injection

• One injector per cylinder• Mounts in intake

manifold, sprays directly at intake valve

• Fired in groups or individually (SFI)

• Ram Tuning for denser air charge

• Lower A/F temps• Leaner mixture during

warm-up

Bosch & Delphi Multec

Fuel Pressure Regulator• Located at end of fuel rail• Maintains constant pressure at injectors• Internal chamber contains a diaphragm

– Pressurized fuel on one side– Manifold vacuum & spring tension on other

• Manifold vacuum pulls up on diaphragm, metering fuel that is returned to tank

• Excess fuel pressure can overcome spring tension, allowing fuel to return to tank

• Increases in manifold pressure causes spring tension to push diaphragm down, blocking return line, increasing pressure in rail.

Fuel Pressure Regulator

Fuel return

Vacuum hose connection Fuel rail

Fuel Pressure Regulator

Central Port Injection (CPI)

• Injector located in center of intake manifold

• 60 psi system• 6 or 8 poppet

valves attached to one TBI type injector

Central Multi-Port Injection (CMPI)

• Similar to CPI

• Individual injectors, with poppet valves

CMPI Connections

Electrical Connectors Fuel Supply Fuel Return

CMPI Up Close

Fuel Pressure Regulator

Cylinder Numbers

Poppet Nozzles

• Contains a check ball & extension spring

• Regulate the flow of fuel into cylinder

• Fuel flows when pressure exceeds 40 psi

• Ball reseats when pressure drops

Injector Testing

• Coil Test – Specific current supplied, measures voltage drop

• Injector Balance – Inj. Energized for a precise time frame, record fuel pressure drop

Injector Circuit Testing• Noid lights• Simple test light that plugs into injector

connector• Light flashes with each electrical pulse

Injector Cleaning

• Periodic cleaning removes varnish & other deposits

• Pressurized canister dispenses cleaning solution

• MUST disconnect fuel pump!