Sorry, this article is currently incomplete. We'll have this finished up soon. In the meantime, check out some other articles on Cars Simplified!Passing an emissions test can get really expensive if your vehicle is older and/or in poor condition, especially if you don't have all the tools to diagnose the issue(s) causing the heightened emissions.
PCV Valve
(Unconfirmed Method) Diverting the tube that lets the PCV Valve will prevent oil vapors from entering the intake air, keeping the intake air cleaner. Motor oil is more difficult to burn and is more chemically complex than gasoline. The vapors from the PCV valve will need to be diverted elsewhere, and venting to atmosphere will lead to an automatic failure if found during an inspection.
Fuel Additives
Fuel additives won't fix a glaring mechanical issue, but fuel system additives designed for reducing emissions offer improved chances of passing, and some manufacturers offer some degree of guarantee. Typically, these will also clear up carbon deposits as well, which will improve engine performance in engines that had carbon build-up (very likely in older vehicles) in the combustion chamber.
Some additives even intend to clean the catalytic coverter, a component that alters the chemistry of the emissions on their way out of the exhaust. These components can get contaminated and/or clogged up over time when other issues are present.
General use fuel system cleaners may also help improve a poor emissions situation, but may be less effective with their less-targeted chemistry. Carbon deposit build-up can alter engine emissions to some degree, but typically an ECU can adjust long term fuel trim to deal with the effects of cabon build-up. If carbon build-up gets bad enough that the ECU can't handle it, a loss in power/performance will be felt.
- Some emissions tests just plug into the OBD port and check to make sure everything is working correctly. However, you can't just clear the codes and go to the test before the codes show up! The test also makes sure the components have had enough time to be properly tested since the codes were last cleared.
- If you check an OBD-II trouble code and it says there is a problem with a particular component, it doesn't mean replacing it will fix the issue. Some components will produce a code if they detect a problem, such as a knock sensor.