If the analyzer does not respond, check to see if one of the following conditions exists:

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 exhaust system.)

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 check.)

Run the analyzer through the test calibration series only after the engine has been brought to operating temperature.

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 manufacturer's 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 SYSTEMS

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 following advantages:

Fuel delivery can be measured with extreme accuracy, giving the potential for improved fuel economy and performance.

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 efficiency high.

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 fuel

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