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Smog Test Prep, Part 1

How to pass with distinction

Nobody likes to fail a test, even if it's just the emissions check on your vehicle. For those of you who have been traumatized by, or wish to avoid the trauma of failing a Smog Test—we have good news. No, you have not won a new car, but the following info can help your car run as good as new, and pass that test on the first try.

Types of Tests

You might be surprised to know that there are three types of Inspection/Maintenance (I/M) vehicle emissions tests currently being administered in the U.S. In rural areas, there is the Stationary Test. This differs from the others in that the tailpipe emissions portion of the test is done with the vehicle, well, stationary.

The second is the standard Loaded Mode Test. This test is performed in urban areas. In this test, tailpipe emissions are sampled while the vehicle is run under a prescribed load on a chassis dynamometer. Sampling is first done at a steady 15 mph, then again at 25 mph.

The third and most stringent of the tests is the I/M 240 test. This test is performed in critical urban areas. It simulates a 2-minute, 40-second road test, covering most typical driving conditions. The city of Denver, CO uses it due to the altitude and local topography.

Test Phases

There are three phases of these tests: Comprehensive Visual Inspection (CVI), Functional Check (FC), and (Tailpipe) Emissions Test (ET). We'll start by covering the CVI, and get to the others in a second article.

The visual inspection is for making sure that all of the emission components that were originally installed on the vehicle are present and accounted for. The functional check ensures that selected key components are actually working properly. The tailpipe emissions test verifies that the engine is in proper mechanical shape, its management systems are working, and the exhaust emission control components are functional.

The first thing that must be considered when prepping your vehicle is the type of test that is being administered in your area. Obviously, the more stringent I/M 240 test will probably be more costly to prepare for. It's not likely, however, that you'll be able to get away with taking your car to a rural area for the simpler Stationary test.

Check Stations

If you need a smog check for the purpose of re-registering your vehicle, you'll want to note if there are special instructions for which type of check station you need to visit. Some States have two different types: a Test/Repair and a Test Only station. They do this for a number of good reasons. Primarily this is to monitor and update their database on vehicle model emissions and Test/Repair facility performance.

At any rate, the DMV paperwork will specify which one you must go to. Some folks like the convenience of taking their vehicle to a Test/Repair facility, and leaving it for needed repairs and a re-test. Unfortunately for them, if the paperwork specifies "Test Only," that won't be possible. Instead, they'll have to take the car to the Test Only facility, and then if it fails, they will have to have it repaired elsewhere. They'll then have to take it back to a Test Only facility for another test! Trauma. At that point, they'll wish that they had done the prep work first.

DIY Check

Once you have established the proper type of test station, you will first want to check your vehicle for issues that will cause a CVI failure. Topping that list would be its mechanical condition. In many cases, the only mechanical failure that would cause a CVI failure is a liquid fuel leak. However, there are many other mechanical conditions that, while not specifically covered by the test, may give the inspecting tech cause to decline testing the vehicle.

These would include other major fluid leaks, loud noises from the engine bay, visible signs of overheating, or any other condition signaling imminent breakdown. Obviously, you'd be advised to address those issues beforehand.

On tests involving the dynamometer, there are other mechanical conditions that may not become apparent to the tech until the test is underway. These conditions may cause the test to automatically abort, or give cause for the tech to do so. They would include problems involving the driveline, such as a slipping clutch or automatic transmission slip, inoperative gears, propeller shaft or drive axle problems-even mismatched, improperly sized, or under-inflated tires.

Now we can continue with preparations for passing the CVI. It's critical that all emission-control components that originally came with the vehicle are in place. Most of the problems in this area come from attempts at modification, which often result in components being removed. Vehicles that have been used for competition have often been tampered with in some way.

Owner Onus

Although it's the legal responsibility of the seller of a vehicle to have it emissions tested before selling, many times it does not work that way. Then the new owner is left with the headache of putting the pieces back together!

Typical components that are removed or altered include the Thermostatic Air Control, Vacuum systems, Air Injection systems, Fuel Evap systems, Catalytic Converters, and Computer Controlled Carburetion systems. If you find yourself with such a vehicle, you would seriously want to count the cost before attempting to put everything right. Otherwise, you may proceed to the next point of inspection.

If you have a carbureted vehicle, check to make sure that the hot air ducting tube is intact. It should attach to shielding around the exhaust manifold and connect to the air cleaner housing near the mixer vacuum servo. These commonly deteriorate and may fall off, which will cause a CVI failure. Replacing this component is cheap and easy.

If your vehicle has an Air Injection (Smog) Pump, make sure that the belt is in good condition and tight enough. If it has gone missing, make sure that the pump still turns smoothly before replacing the belt. If not, both belt and pump will have to be replaced. Problems here will cause a CVI failure.

Have a look at the fuel filler cap, and inspect the filler neck for damage or tampering. A missing or obviously incorrect cap or damaged neck will cause a CVI failure.

Next, check the Check Engine/Service Engine Soon-Malfunction Indicator Lamp (MIL) for proper operation. If it doesn't illuminate when the ignition key is turned to the "on" position, or if it stays on while the engine is running or the car is being driven, it will cause a CVI failure. You may want to enlist the help of a trained service pro to sort such a problem out.

That covers the important points involving the Comprehensive Visual Inspection part of the test. In part two, we will address the Functional Check and Emission Test portions of the test. Class dismissed!