Idle Speed/Ignition Timing/OXS-Duty Cycle (CO Value), Checking/Adjusting
(1984 Rabbit Carburetor)Work sequence
Test conditions:
^ oxygen sensor connected
^ engine oil temperature minimum 80~C (176~F). Radiator fan must come on at least once
^ all electrical consumers switched OFF (radiator fan must not be running while adjusting)
^ transmission in neutral
- connect tester according to manufacturer's instructions
Note TDC sending unit must fit snug into transmission housing
- remove PCV valve from valve cover (arrow)
- remove cap from CO probe receptacle and connect CO tester
- disconnect both wire plugs at idle stabilizer and connect both of them together (arrow). Check connector plug terminals for good connection
- check idle speed
^ 920 RPM +50/-30
- if out of specification, adjust to 920 RPM+50/-30 (890 to 970 tolerance) by turning screw A on the throttle lever
- disconnect vacuum advance (right arrow) at distributor and plug hose (no vacuum retard diaphragm used)
- check timing and adjust if necessary
^ 2~ BTC +/- 1~
- reconnect vacuum retard hose at distributor
- readjust idle speed if necessary
- turn ignition OFF
- disconnect dwell lead on tester from ignition coil terminal 1 and connect to oxygen sensor test connection (blue/white wire) on strut tower using adapter US 1112
- remove test leads from spark plug wire (cylinder 1) and TDC sending unit
- press in % button on tester
- start engine
- check duty cycle and CO%
^ OXS-duty cycle must be according to chart 1 (reading must fluctuate)
^ CO must be less than 1.5%
- if duty cycle or CO% out of limits, remove carburetor
- remove tamper-proof plug (arrow) from idle mixture screw
- reinstall carburetor
- turn idle mixture screw to adjust duty cycle. Turning screw clockwise, lowers duty cycle reading; turning counterclockwise, raises reading
^ OXS-duty cycle must be according to chart 1 (reading fluctuating)
^ Less than 1.5% CO
- turn engine OFF
- install new tamper-proof plug
- readjust idle speed if necessary
- reconnect vacuum advance hose at distributor
- reconnect idle stabilizer
- reinstall PCV valve to valve cover
- remove CO meter and reattach cap to probe receptacle
- for duty cycle adjustments use chart 1 below. This chart is necessary because of the introduction of a barometric cell in the electronic control unit. Once the idle duty cycle is set correctly, with use of the chart, the barometric cell will automatically adjust the duty cycle according to changing barometric pressure (altitude).
^ examples of correct duty cycle settings:
at sea level 25% +/- 10% at 3000 feet 38% +/- 10% at 6000 feet 50% +/- 10%
OXS sensor, checking
- start engine
- warm engine until coolant at least 55~C (130~F) Please note all duty cycle values are dependent upon altitude. During all duty cycle readings the technician must use the charts provided to determine what the duty cycle value should be in relation to the altitude at his/her location.
- disconnect wire to OXS sensor
^ duty cycle should be at a value shown on chart 1 (reading steady)
^ For example at sea level the value should be 25% +/- 10% at 3000 feet the value should be 38% +/- 10%
Rich mixture limit check
- Ground OXS sensor wire
^ duty cycle should be at a value as shown on chart 2
^ For example at sea level the value should be 0% +/- 10% at 3000 feet the value should be 15% +/- 10%
Lean mixture limit check
- apply 1.5 volts to OXS sensor wire
^ duty cycle should be at a value as shown on chart 3
^ For example at sea level the value should be 70% +/- 10% at 3000 feet the value should be 85% +/- 10%
Cold running enrichment check
- disconnect wire to OXS sensor
- disconnect wire to OXS temperature sensor Duty cycle should be at a value as shown on chart 4
^ For example at sea level the value should be 15% +/- 10% at 3000 feet the value should be 30% +/- 10%
OXS relay check
- check with ohm meter
- should show continuity between terminals 85 and 86
- circuit closes from terminals 30 to 87 with ignition ON, opens with ignition OFF