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Old 05 Jul 2013, 02:32 am
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Default what would cause carbon monoxide levels to be high on 95 honda civic lx?

all tests look good except for the Co section on smog results. I changed air filter plugs wires map sensor o2 sensor up stream
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Old 05 Jul 2013, 02:46 am
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catalytic converter is supposed to take the CO down and produce water vapor and CO2. do you have a check engine lamp on for a P0420 Catalyst system low efficiency?
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Old 05 Jul 2013, 03:02 am
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Just get your ride checked for error code. You can be able to know the cause of deposition of CO. Generally catalytic converter absorbs CO to reduce the emission hazards. I would recommend you to get your ride checked for error code to know the exact cause of problem.
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Old 05 Jul 2013, 03:22 am
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No P0420 on a 1995 Honda - it is OBDI. The limited reporting of the Honda OBDI system also means you probably won't find anything useful in the codes. Just in case, see the first source for how to retrieve the codes. Where it talks about a "code reader" it is just a shorting tool - most people use a paper clip.

A full report of the emissions would really help. Mostly I would be interested in what the standards are and what the readings are for CO and NOx at the low and high speed tests. I can just give you the long-winded view instead and let you sort it out.

CO has only one basic cause - too much fuel is being injected for the amount of air. There is a frustrating quirk in emissions testing: the report gives the highest reading during that part of the test cycle, and we don't know if the number is what it settles down to after it gets to the speed or if it is part of the acceleration to the speed. I once had a 1984 Dodge that failed on 5% CO at cruise, a radically high reading, and it turned out it was only generating a puff of CO when the throttle was lifted after hard acceleration to the cruise test speed. So it could be your engine is working normally most of the time and failing when disturbed, or it could be too rich all the time. The color of the spark plug insulators is a time-honored indication of mixture - if the insulators are light tan you can be pretty sure the CO is just spiking but if they are dark the engine is running rich a lot of the time. Better yet, if three are tan and one is dark you can be pretty sure you have a leaky fuel injector on that cylinder and that is almost certainly the problem. Otherwise you can scratch the injectors themselves off the suspect list.

My interest in the NOx is because of the relationship between NOx and CO. NOx is catalyzed in the first stage of the converter if there is not too much free oxygen. In fact, by the time free oxygen reaches 2% (free oxygen in air is 21%) the converter can't reduce NOx. If the engine is running rich all the time NOx will be suspiciously low, much below the allowed amount. If it is just spiking rich, NOx will pass but not by a huge margin.

You have done a good job so far of selecting suspects. The air filter replacement can't hurt, might help, and is good practice. The MAP sensor could certainly produce high CO and would be hard to pin down, and the O2 sensor was sluggish as an old hound at 18 years old. Those rule out a lot. My interest falls on fuel injection next. The computer uses the MAP output to decide how long to hold the fuel injectors open each time, and it relies on proper fuel pressure to deliver the right amount of fuel . (The O2 sensor just supplies feedback to say a little less or a little more... the mixture has to be nearly correct already.) If the fuel pressure is too high it will deliver too much fuel and CO will be high. Measuring fuel pressure when the engine is running is a bit of a headache because the pressure depends on the intake manifold pressure, but you can see if it is obviously high. Or you can "shotgun" out the fuel pressure regulator - they are pretty reliable devices so I would just get one from a wrecking yard and see if it makes a difference. Again the plug color is a good clue - if the plugs look normal the regulator you have is working at least most of the time.

The second source has some great background on how the emissions react to operating conditions.

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