hoping you can bring an old-timer up to speed on fuel injection. I
used to be pretty good at fixing things but hadnít even considered
trying to work on this one. Iíd feel better driving if I had an
idea whatís going on under the hood.
here goes: A typical fuel-injection system utilizes three general
processes: fuel pressure, thinking/processing and fuel delivery.
Fuel pressure involves the use of an electric fuel pump inside or
near the fuel tank. The pump sends fuel to the fuel rail, a pipe of
sorts thatís attached to the engine and the fuel injectors. There,
a pressure regulator holds a specified pressure and returns unneeded
fuel to the tank. Recent vehicles house the regulator in the fuel
tank and send forward only the fuel thatís needed.
thinking/processing part employs a control unit typically called an
electronic control module/powertrain control module, or ECM/PCM. In
addition to managing the fuel pump, this very smart box receives
information from a dozen or more engine and transmission sensors.
This information indicates engine and vehicle speed, load,
temperature, airflow, throttle position, altitude and gear
selection, just to name a few. Incoming data is crunched with
programmed instructions resulting in appropriate commands being
issued to fuel, ignition, transmission and emission-control
manage the delivery of metered, misted fuel, which next vaporizes in
the intake manifold on the way to the engineís combustion
chambers. Each brief electrical pulse sent from the ECM/PCM to these
electromechanical showerheads results in a precise shot of fuel just
as each intake valve opens. Very recent vehicles take this a step
further and shoot highly pressurized fuel directly into each
combustion chamber. Fuel injection is vastly superior to carburetors
of the past. Now, each engine cylinder receives a more evenly
matched quantity of fuel, fuel is more precisely atomized (misted),
and there are far fewer quirky mechanical things to go awry.
thinking/processing part now comes back into play, monitoring
exhaust oxygen content. This information allows fine-tuning and
corrections to be made to fuel-injection commands, in compensation
for minor problems or wear and tear. If a problem develops that
could threaten emission compliance, and to a lesser degree engine
performance, the onboard diagnostics system lights the "check
engine" lamp, stores a trouble code, and records a snapshot of
systems are incredibly reliable. When service is needed, a scan tool
provides access to trouble codes, sensor data, fuel trim or
fine-tuning information, actuator commands, the data snapshot and
additional diagnostic information. Fuel pressure may also be checked
by connecting a pressure gauge. Typical problems, while very rare,
include a worn-out fuel pump, with a lifespan perhaps of
100,000-150,000 miles; dirty fuel injectors; and sensor or
connection faults. Most are fairly easy to diagnose and repair.