Question about 1991 Honda Civic
Not knowing the history or why it's failing is tough to determine.
If it's due to a vapor emission issue, you'll need to check the filler tube on the fuel tank for a minor crack or rust through. Usually this can be done after driving the car and getting up close and smelling for any fumes, following them to the source. Use epoxy sealer to fill the hole or crack if this is an issue. I found this was usually due to gravel hitting against that pipe causing it to then rust leaving minor pits & holes.
Tune-up, is the car running properly? If not, a tune up is imperative. IF you have had it tuned and parts replaced, make sure the Air filter was one of the items.
Make sure your oil is fresh and has been recently changed. Oil viscosity has a direct effect on engine performance and the amount of bypass fumes are put into the exhaust as the engine is runnning, as well as affecting valve clearance.
Go to an autoparts store and by some cleaner for your emission system. also, add a little octane booster and if you fill your car up before testing, use Premium fuel, or at least fuel at a higher octane level, this produces less emissions as it causes a better fuel burn.
If you haven't seen the cure up to now, you may need a new catalytic converter, have yours tested by a reputable service center. Converters get hotter than the exhaust when working properly, if the converter is at the same temp as the pipes coming into it, it's not working.
Posted on May 15, 2010
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Posted on Jan 02, 2017
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The PCM also uses this information in order to manage the fuel system for maximum efficiency. The most obvious symptom you will see is the A/T gear position indicator lights will not come on or come on in the wrong position.
Once this is repaired emissions should pass
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