Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Co-Adjustment Using VOLVO Mono Tester
- Connect Mono-Tester to the Batter positive and negative posts, HT wire for No. 1 cylinder, ignition setting sensor/stroboscope, CO test point (pink wire). Warm up and run the engine at 1500 rpm.
- Check the idle speed.NOTE: Run the engine until themostat has opened and then for a further 10 minutes.
Close idle control valve by grounding blue-white lead in connector on left-hand wheelhouse. Switch off A/C as applicable. Adjust engine speed w/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 controls. See THROTTLE VALVE, SWITCH, LINKAGE ADJUSTING
- 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. Ignition setting should be 12°BTDC at idle. Adjust setting by turning distributor body.
- Check CO level. Turn adjustment knob on Mono-tester to 4-cyl. At correct CO level, pointer should move between 20°-70°.
- CO should only be adjusted after all possible faults have been checked/rectified. Remove seal. Turn off engine. Drill two 2mm (0.08") holes in plug. Withdraw plug w/circlip pliers and start engine. Adjust CO so that Mono-tester pointer moves between 20°-70°. Turning the adjustment screw counterclockwise reduces the CO and turning clockwise increase CO. 15 turns is the range for the adjustment screw. Always use a new seal CO adjustment screw plug. Push plug into position. Disconnect test instruments.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.