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 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.) l 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. 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 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 5-3