If the analyzer does not respond, check to see if one
of the following conditions exists:
l The vehicle is not at operating temperature.
(Warm up the engine by normal running.)
. The probe is not inserted far enough into the
tailpipe of the vehicle. (Remove and reinsert the probe.)
. Check the vehicle for an exhaust leak. (Repair the
. Check the mode switch of the unit you are testing
with reset switches.
. The analyzer sampling system leaks. (Check for
tight connections at both of the IR hoses. Check the
O-rings in the filter bowl of the analyzer. Perform a leak
l Run the analyzer through the test calibration
series only after the engine has been brought to
Adjust the cold- and hot-idle speed of the engine.
Assuming all other parts of the engine and its controls
are working properly, use the specifications provided by
the manufacturers repair manual to adjust the
carburetor to meet the minimum ppm of HC, CO, and
C02 emissions. Return the vehicle to the shop
supervisor for final inspection and return it to service.
GASOLINE FUEL INJECTION
Fuel injection systems are an increasing y popular
alternative to the carburetor for providing an air-fuel
mixture. They inject, under pressure, a measured
amount of fuel into the intake air usually at a point near
the intake valve. Fuel injection systems provide the
. Fuel delivery can be measured with extreme
accuracy, giving the potential for improved fuel
economy and performance.
l Because the fuel is injected at the intake port of
each cylinder, fuel distribution will be much better and
fuel condensing in the manifold will not be a problem.
. There is no venturi as in a carburetor to restrict
the air intake, making it easier to keep volumetric
. The fuel injector, working under pressure, can
atomize the fuel much finer than the carburetor,
resulting in improved fuel vaporization.
There are three basic configurations of gasoline
injection: timed, continuous, and throttle body.
TIMED FUEL INJECTION SYSTEMS
In gasoline engines, the timed fuel injection system
injects a measured amount of fuel in timed bursts
synchronized to the intake strokes of the engine. Timed
injection is the most precise form of fuel injection; it is
also the most complex. There are two basic forms of
timed fuel injection: mechanical and electronic. The
operation of the two are very different and will be
covered separately in the following two paragraphs.
Mechanical-Timed Fuel Injection
The mechanical-timed injection system (fig. 5-1)
has a high-pressure pump that draws fuel from the gas
tank and delivers it to the metering unit. A pressure relief
valve is installed between the fuel pump and the
metering unit to regulate fuel line pressure by bleeding
off excess fuel back to the gas tank. The metering unit
is a pump that is driven by the engine camshaft. It is
always in the same rotational relationship with the
camshaft so that it can be timed to feed the fuel at just
the right moment to the injectors. There is one injector
for each cylinder. Each injector contains a spring-loaded
valve that is opened by fuel pressure injecting fuel into
the intake at a point just before the intake valve. The
throttle valve regulates engine speed and power output
by regulating manifold vacuum, which, in turn,
regulates the amount of fuel supplied to the injectors by
the metering unit.
Electronic-Timed Fuel Injection
In an electronic system (fig. 5-2), all of the fuel
injectors are connected in parallel to a common fuel line
that is fed by a high-pressure pump from the gas tank.
A fuel pressure regulator is installed in line with the
injectors to keep fuel pressure constant by diverting
excess fuel back to the gas tank, Each injector contains
a solenoid valve and is normally in the closed position.
With a pressurized supply of fuel behind it, each injector
operates individually whenever an electric current is
applied to its solenoid valve. By sending electric current
impulses to the injectors in a sequence timed to coincide
with the needs of the engine, the system will supply
gasoline to the engine as it should.
For this function and that of providing the proper
amount of fuel to the engine, the system is fitted with an
electronic computer to time the impulses. The computer
receives a signal from the ignition distributor to