Computers and Control Systems: Testing and Inspection

OXYGEN SENSOR SYSTEM - CHECKING

The oxygen sensor system was designed to be maintenance free and normally no adjustments are required. However, if a performance problem does occur the system can be checked by using a dwell meter such as Sun TDT-11, Siemens 451, or equivalent. The dwell meter is used to measure the "duty cycle" produced by the oxygen sensor control unit.

Using the information on the following pages you will be able to adjust initial CO% and check the operation of the oxygen sensor system. When checking the oxygen sensor system, if you have any dwell meter readings which are out of "specs". repair the problem before continuing.





Connect a dwell meter (Sun TDT-11 or equivalent) to the test connection located behind the throttle valve housing.





Using an adaptor connect the dwell meter "plus" lead to the blue wire with brown tracer and the "minus" lead to ground. "Zero" the dwell meter and set it to the 4 cylinder scale.

Hooking up Siemens 451:
Connect "+" lead to a power source.
Connect "-" lead to ground.
Adjust tester to 4-cylinder operation.
Connect dwell lead (blue connector) to oxygen sensor test connection using dwell meter adapter.

Note: Do not connect any of the other test leads to the engine. This would result in incorrect readings.

Prepare car for CO% adjustment:
Run the engine until it reaches operating temperature (radiator fan must have come on at least once) disconnect crankcase breather hose from valve cover and plug hose.
Cars without idle stabilizer - Turn the headlamp highbeams on and turn the air conditioner and all other electrical accessories off.





Cars with idle stabilizer - Turn all electrical accessories off, bypass the idle stabilizer which is located in the water drain tray by removing the two multipoint connectors from the idle stabilizer control unit and connecting them together.

Adjust idle speed and ignition timing:
Idle speed - 940 ± 60 RPM
(900 ± 100 RPM for 5 cyl.engine without idle stabilizer)
Ignition timing -- 3° after TDC (1979 Audi 5000 with automatic; 6° before TDC).
(1980 5000 Turbo; 21° before TDC at 3,000 RPM with vacuum hoses off).

Remove and plug crankcase breather hose.





Remove the metal probe from the CO meter hose and connect the hose to the CO test point.
Disconnect the oxygen sensor wire (bright green wire by exhaust manifold) the dwell meter should read 45° ± 2°.





Connect the green wire from the control unit to ground:
The dwell meter should read at least 75°.
CO reading should increase.





Connect the "+" terminal of a 1.5v size D flashlight battery to the green wire from the control unit.
Connect the "-" terminal of the battery to ground:
The dwell meter reading should decrease to less than 12°
CO reading should decrease.





Insert adjusting tool P377 and adjust CO% to 0.8% ± 0.4%
(always check engine sticker for latest specifications)
Turn CO adjustment screw.
in - raises CO%
out - lowers CO%
Remove tool after each adjustment.
Accelerate engine briefly before reading CO gauge.
Reconnect the oxygen sensor wire.
The dwell meter reading should now fluctuate.
CO reading should be 0.8% ± 0.4%.





Reconnect the PCV hose.
Readjust idle speed to 940 ± 60 rpm.
Shut off the engine and reconnect the idle stabilizer.
Check ignition timing at idle:
Timing may vary from -3° to +3° if timing is incorrect replace idle stabilizer.
Load engine by switching on.all electrical accessories.
Ignition timing will advance if idle stabilizer is working.