Service Manual

4.18
ELECTRONIC FUEL INJECTION
FUEL INJECTORS
Operation Overview
NOTE: All EFI units utilize quick connect fuel lines.
The fuel injectors mount into the cylinder head, and the fuel rail
attaches to them at the top end. Replaceable O-rings on both
ends of the injector prevent external fuel leaks and also insulate
it from heat and vibration.
When the key switch is on, the fuel rail is pressurized, and
voltage is present at the injector. At the proper instant, the ECU
completes the ground circuit, energizing the injector. The valve
needle in the injector is opened electromagnetically, and the
pressure in the fuel rail forces fuel down through the inside. The
“director plate” at the tip of the injector (see inset) contains a
series of calibrated openings which directs the fuel into the
intake port in a cone-shaped spray pattern.
The injector is opened and closed once for each crankshaft
revolution, however only one-half the total amount of fuel
needed for one firing is injected during each opening. The
amount of fuel injected is controlled by the ECU and determined
by the length of time the valve needle is held open, also referred
to as the “injection duration” or “pulse width”. It may vary in
length from 1.5-8 milliseconds depending on the speed and load
requirements of the engine.
Fuel Injector Service
Injector problems typically fall into three general categories-
electrical, dirty / clogged, or leakage. An electrical problem
usually causes one or both of the injectors to stop functioning.
Several methods may be used to check if the injectors are
operating.
• With the engine running at idle, feel for operational
vibration, indicating that they are opening and closing.
• When temperatures prohibit touching, listen for a
buzzing or clicking sound with a screwdriver or
mechanic's stethoscope.
• Disconnect the electrical connector from an injector and
listen for a change in idle performance (only running on
one cylinder) or a change in injector noise or vibration.
NOTE: Do not apply voltage directly to the fuel
injector(s). Excessive voltage will burn out the
injector(s). Do not ground the injector(s) with the
ignition on. lnjector(s) will open/turn on if relay is
energized.
If an injector is not operating, it can indicate either a bad injector,
or a wiring/electrical connection problem. Check as follows:
Injector leakage is very unlikely, but in rare instances it can be
internal (past the tip of the valve needle), or external (weeping
around the injector body). The loss of system pressure from the
leakage can cause hot restart problems and longer cranking
times.
Injector problems due to dirt or clogging are unlikely due to the
design of the injectors, the high fuel pressure, the use of filters
and the detergent additives in the gasoline. Symptoms that could
be caused by dirty/clogged injectors include rough idle,
hesitation/stumble during acceleration, or triggering of fault
codes related to fuel delivery. Injector clogging is usually caused
by a buildup of deposits on the director plate, restricting the flow
of fuel, resulting in a poor spray pattern. Some contributing
factors to injector clogging include; dirty air filters, higher than
normal operating temperatures, short operating intervals and
dirty, incorrect, or poor quality fuel. Cleaning of clogged
injectors is not recommended; they should be replaced.
Additives and higher grades of fuel can be used as a preventative
measure if clogging has been a problem.
Fuel Injectors
Fuel Rail