In California an older car built after 1975 has to pass a rigorous smog test every two years. If your car does not pass you generally cannot register it for operation on the street.  That year is fixed and means that as time goes on classic cars built after 1975 could be many decades old and will still need to pass the smog test for registration in California.  If a car fails the test you have to repay the $50 or more fee for the test agfer you fix the problem and retest the car. Worse though – that fact is listed on the record and even if the problem is rectified the past failure of the car and could raise concerns with future purchasers.  It is wise to take a close look at the numbers of your test certificate each time you test and note if you are creeping towards a fail.   If so you should take action before two years are up and you need your next test.  For many people, this testing cycle is a disincentive to purchase classic and sports cars built after 1975.

Now, the smog test in California includes a visual inspection to make sure all of the original smog equipment is still on the car, connected and appears functional.  There is a check list the technician will follow for the visual. The timing will also be tested to make sure it is within given parameters.  The inspector will also look to see if there is white or black smoke issuing from the exhaust pipe when the car is running. If you have a newer classic with a Check Engine light – if this light is on during the test it is an automatic failure.  The real test for most cars comes when a probe is placed in the tail pipe and the car is run on a set of rollers at 15 and 25 MPH.  The critical values from this dynamic testing are Hydrocarbons (HC PPM), Carbon Dioxide (CO %)  and Nitrous Oxides (NO PPM).  The Vehicle Inspection Report (VIR) given to you when you test shows you the values your car produced, average values for these measures and finally the maximum value allowed.  The maximum values are based on your car’s year, weight and engine size. This is a good thing because it means a 1976 car does not have to meet the more stringent targets set for a 2006 car.  The average values provided are based on the year, make and model of your car.  If your car pumps out more that that maximum allowed value of HC, CO or NO you fail the test.

In terms of general precautions prior to a smog test here are 7 steps –

1. Make sure you have good fresh fuel in the tank and fuel system with appropriate octane rating.  Classic cars may sit for long periods and fuel go off.

2. Put in a new air filter.

3. Make sure all your smog equipment is hooked up and hoses, wiring sensors and wiring connected.

4. Make sure your fuel filter, pump, carb or fuel injection system is clean and functioning well.

5. Put in new plugs and make sure your the rest of your ignition system is in top shape (points clean, wires good, timing and dwell correct etc.)

6. Fresh oil and filter is not a bad idea.

7. Run the car and make sure it is warmed up before the test. If you have a newer classic with catalytic converter make sure it is good and hot by running the car at speed.  The catalytic converter is more efficient when hot.

Your last VIR can provide important information on what measures are creeping towards failure. In addition, you can pay to have a test only analysis that is not forwarded to the Department of Motor Vehicles ( DMV ) and act on that before taking an official and recorded test.Having specific information on if HC, CO and/or NO is at the failure point can help you diagnose the problem and repair prior to the official test.

High HC –  Poor compression, bad timing or ignition connections, poor fuel mixture, bad air injector (when fitted), bad catalytic converter (when fitted).

High CO – Fuel mixture too rich, injection and smog equipment sensors, connections not functioning (when fitted), engine temperature too low for good combustion, bad catalytic converter (when fitted).

High NO – Fuel mixture too lean, defective smog equipment (when fitted), bad catalytic converter (when fitted).

Two years ago I ran my wife’s 1986 Alfa Romero Spider Veloce (Motorphile Nov. 22, 2010) through its smog inspection and was concerned about high values in HC, CO, NO.  The car passed, but the numbers were not good.  Now, when all three values (HC, CO, NO) are bad and the car is well tuned, with good compression etc. the likely culprit is the catalytic converter.  The cats do break down over time – and in some cases if you shake them you can hear a rattle.   I could hear this on the Alfa.  So, as the next smog check approached I decided to install a new catalytic converter.  Read the next article to see the installation and if the Alfa passed the test or not!