The O2 sensor could be next. A certified smog check repair station will have
to find out if your vehicle is in proper fuel control. The diagnosis should
begin with inspection of the air/fuel "feedback" system. This includes
ensuring the oxygen sensors are working properly, the emissions computer
system is receiving signals from the oxygen sensor/s, the computer is
computing the data properly and sending the correct signals to the fuel
injectors to either increase or decrease fuel delivery to the combustion
chambers.
The feed back test will utilize a 5-gas analyzer (the smog machine can be
used for this test) and propane. The smog technician will introduce propane
to the intake system and ensure the oxygen sensor is sensing the propane as
an increase in CO (carbon monoxide), and ordering the emissions computer to
decrease fuel delivery the instant propane is added to air intake stream.
This test should be done after the engine has sufficiently warmed up and
while it is running at idle. If no change in fuel delivery is seen there is
feedback problem. The diagnose then should turn to which part of the
feedback system is not working right. Using a multimeter voltmeter the smog
repair mechanic should observe the voltage output of the oxygen sensor as
propane is added. The voltage coming from the oxygen sensor should increase.
If no voltage increase is seen the O2 sensor is not working. The sensor
should be replaced and the test started over. If voltage increase is noticed
the smog technician needs to ensure voltage increase is also present at the
computer input terminal. If voltage is present at the terminal as well next
the technician must ensure the emissions computer output to the fuel
injectors are lowering "injector pulse rates". At the end of the fuel system
feedback test it will be know whether the high emissions your vehicle is
producing is an electronic or mechanical fault. The technician can then
further diagnose the failure.
