The Ignition Timing Test applies to 1976 to 1995 model-year vehicles equipped with adjustable timing.

If the under-hood emissions control label, an emissions application guide, or other reliable manufacturer derived references indicates timing is not adjustable, then the Ignition Timing Test is not required.

Smog-Check-Ignition Timing

Inspectors shall check the base ignition timing using the vehicle manufacturer procedures. Many under-hood emission control labels provide procedures and specifications for checking the ignition timing.

If the procedures are not on the label, refer to an emission control application guide or an appropriate service manual. If no manufacturer’s engine speed tolerance is given for the timing check, the idle speed shall be within 100 RPM of the manufacturer’s specified idle speed

Smog-Check-Ignition Timing

Pass/Fail Criteria: To pass inspection, the base ignition timing must be within 3 degrees (± 3 degrees) of the manufacturer specification.

If it is more than 3 degrees from manufacturer specification, the vehicle shall fail the functional test.

Note: If the manufacturer specification provides a range, the 3 degree additional tolerance described above is not allowed.

It is important to use the emission application guide and or repair manual for the proper timing specification, timing scale and location, timing marks and the proper procedure to check or adjust the timing. 

Mechanical Defect(s): If the timing cannot be measured due to a mechanical defect, such as a slipped harmonic balancer, the vehicle shall fail the timing test. The EIS includes a provision to account for mechanical defect.

Follow the EIS prompts and document the mechanical defect on the Vehicle Inspection Report. 

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Pre Examination: Smog Inspector Class  Ignition Timing 

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Smog Inspection Pre Exam: Exempt Vehicles