CO% Adjustment Using Volvo Mono-Tester

CO-Adjustment Using Mono-Tester

Connecting Mono-Tester





- Connect Battery (+) and (-) posts
- Connect HT wire for No. 1 cylinder
- Connect Ignition setting sensor/stroboscope
- Connect CO test point (green-white wire).

Check/Adjust Idle Speed
- Warm-up engine
- Run engine at 1500 rpm.

NOTE: Warm-up engine until radiator thermostat opens.

Fig. 326 IDLE SPEED TEST CONNECTOR:

- Ground red-white wire to close idle air control valve.

NOTE: Switch off AC as applicable.

- Check idle speed.





- Adjust engine speed with idle adjustment screw to 700 rpm.
- Disconnect ground from test point.
Engine speed should increase to 750±20 rpm

If values are incorrect: check/adjust Throttle Body and/or Throttle Cable/Linkage.

Check/Adjust Ignition Setting
Idle speed fluctuations can affect ignition setting. Make sure that fluctuations are not greater than 25 rpm.
If greater, check air control valve hoses for blockages.





- Set Mono-tester to display ignition timing.
- Read ignition timing on Mono-tester.
Ignition setting should be 12°+2° BTDC at idle.
- Adjust setting by turning distributor body.

Check CO level
CO should be checked/adjusted within 5-1O minutes of radiator thermostat opening.





- Turn adjustment knob on Mono-tester to 4-cyl.
At correct CO level, pointer should move between 2O°-7O°.

Adjusting CO
CO should only be adjusted after all possible faults have been checked/rectified.

- Turn off engine.

Fig. 370 REMOVE CO ADJUSTMENT SEAL:

- Drill two 2 mm (0.08 in.) holes in plug.
- Withdraw plug with circlip pliers.
- Start engine.
- Adjust CO content so that Mono-tester pointer moves between 2O°-7O°.

Fig. 371 CO ADJUSTMENT:

Counterclockwise reduces CO
Clockwise increases CO
Adjustment range = 15 turns.





- Seal CO adjustment screw
Always use a new plug.
- Push plug into position.
- Disconnect test instruments.