Question about 1991 Honda Civic

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Can't get 1991 Honda Civic to pass an emissions test. What could be some things to check and/or replace?

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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.

good luck.

Posted on May 15, 2010

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1 Answer

I have a 2001 Honda Civic that did not pass emissions test. My


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Jose, I don't know if this will give you the answer you are looking for because there are many things to consider here. The exhaust gas recirculation valve (EGR) is one of the main things involved in reducing NO emissions. This valve is controled by the power control module. (PCM) This is your vehicles computer. The PCM monitors the vehicles speed and will command the EGR to open when the vehicle attains a certain speed, which is why the ASM test being done is recorded at two different speeds. At 25 MPH your vehicle failed the hydrocarbon (HC) emissions limit and this could be for a number of reasons. When is the last time you car was tuned up? Old spark plugs, wires, clogged air filters, oxygen sensors, leaking injectors (personal experience) or the PCV valve could be contributing to the results of the test. I guess that the easiest way to go is to tune up the engine replacing the spark plugs, wires, air filter and the PCV valve and don't forget to have the oil changed at the same time. Only then should have the vehicle retested and see what the results are. Should it fail again you may have to consider having the EGR or the catalytic converter replaced depending on what portion of the test fails. If the NO fails I would consider the EGR. If the HC fails then I would consider the catalytic converter. Good luck with this.

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1 Answer

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If you are getting a Check engine Light let me know, it will make things easier to diagnose.

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hi,  this got fixed . . . all my fuses i checked WERE good . .  BUT, i had taken out my dome light fuse to replace another similar fuse that had blown . . . the mechanic at Honda let me know that the diagnostic system runs through the domelight fuse for some reason - once that fuse was replaced, it was good to go!

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first thing i would check would be your spark control module.Located in the distributer under the rotor.take it down to your local autoparts store for testing.have them test it three times in a row to get it to operating temp.if it passes then check your coil with a multimeter.

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If you failed you should know if it is HC, NOx, or CO. Posting that will make it much easier to diagnose.

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