Look the Part
Oftentimes, your car could pass at the tailpipe but fail a visual inspection. Pop the hood and look for a vacuum hose diagram sticker. Make sure the vacuum hoses in your engine bay match the diagram. If any hoses have come loose, reattach them according to the vacuum diagram. If any are missing, visit your local auto shop and pick up some inexpensive vacuum hose.
Take a look under your vehicle and make sure there are no visible exhaust leaks – particularly at the catalytic converter. If there are massive rust holes in the converter, get it replaced – a damaged cat is sure to get you flagged for failure.
Check the Light, Dummy!
Another common cause of failure could be the check engine light, which some call the dummy light. It’s normal for the light to illuminate when you first turn on and start your car. However if the light stays on long after startup, it’s possible that you may have some emissions related failures even if your car fails at the tailpipe. If the smog tech sees this, be prepared to fail your inspection.
In the event that your MIL or CEL is on (that’s malfunction indicator lamp or check engine light to us regular folks), take it to your local auto parts store and ask them to “pull the code” for you. Most auto parts stores have little computers that they can interrogate your car’s computer to see what’s causing the light to go on, as well as reset (turn off) the light if need be. The best part is – they will usually do this for free.
Tune It Up
If your car is running rough or misfiring, this will definitely affect your emissions. A lot of places charge varying rates for a tune-up, but you can do the biggest component of this routine in your driveway by changing your sparkplugs. When sparkplugs become worn, they fail to completely ignite the air-fuel mixture in your engine, causing more unburnt pollutants to exit your tailpipe. If you’re remotely handy, you can pick up a new set of plugs at your local auto store for cheap. If not, it shouldn’t take your local mechanic more than fifteen minutes to do it.
Timing Matters
If you have an older vehicle, it will probably have a distributor. The distributor determines when to send current to your sparkplugs (which will subsequently ignite and light off the air-fuel mixture inside your engine). The engine is rated to ignite within a given window in the combustion cycle – measured in degrees. If your car is running outside of this window, the smog tech will fail you. Again, 15 minutes at your local repair shop will get this remedied.
If you’ve come this far, you’ve pretty much accomplished all the common sense stuff. Now if you’re desperate, read on.
Keep it Clean - Part 1
Generations of do-it-yourselfers have sworn by a product called Seafoam Motor Treatment. It should be fairly easy to find at your local auto parts store. Try not to skip this step is the backbone of this list of tips.
Seafoam is basically a magical wonder-solvent designed to clean out the insides of your intake tract and combustion chamber. When sucked through your engine, it will clean out all the dirt and oil deposits in your intake manifold as well as the carbon deposits on top of your pistons. In some cases, cleaning all this crud out can make the difference between just barely failing emissions and just barely passing.
It’s a fairly straightforward procedure, but if you don’t know what you’re doing its possible to severely damage your engine. Rather than incur any liability, I’ll refer you to either your local mechanic. If you’ve got a steady hand and a fair measure of common sense, you can always search for “seafoam” on Google or YouTube. Some of the videos are a sight to see as this procedure will cause a temporary, yet massive cloud of smoke as the Seafoam cleans everything out.
Keep it Clean – Part II
Once you’ve gotten the previous step out of the way, make another trip to your local auto parts store and pick up a bottle of CRC Guaranteed to Pass, better known on internet message boards as G2P. The Seafoam started the job by removing the majority of the gunk, the G2P finishes the job by cleaning up the rest of the deposits and your fuel injectors to boot.
Drive your car until you’re low on gas, add the bottle of G2P to your near empty tank at the gas station, and fill up like you normally would. It might take you a week or two, but drive around until the entire tank of treated fuel has been consumed.
