Question about 1983 Chevrolet Silverado

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What causes high co percentage in emission test

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Measured in percent, this is the result of incomplete combustion. In other words, the fuel mixture has been compressed and ignited, but could not complete the combustion process due to the lack of oxygen. This failure is always mixture or ignition timing related. The ideal reading for CO is 0%. A normal reading for CO is usually around .25 to .75% with 1.2% being the failure mark in most areas for vehicles 1984 and newer. Earlier cars are allowed higher readings. Any car equipped with an Oxygen sensor will try to run under 1.0% as measured before the Catalytic converter (use that test connection for set-up). A vehicle with a CAT, O2 sensor, and an AIR system (Air Injection Reaction) will read almost 0% with everything working properly.

Posted on Oct 06, 2009

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Too much unburned fuel. I'm thinking your carbureted, so check choke working properly, air mixture isn't too rich, as well as ignition timing isn't too far advanced, will all cause higher reading. Fresh fuel and a good hot run down the highway will help prior to test as well.

Posted on Oct 06, 2009

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1 Answer

What does it mean when it says co


CO? That means Carbon Monoxide - it's a rather toxic and poisonous gas emitted from the exhaust system.

When they check emissions on cars CO is one of the gases they measure. If the level is too high .. your car fails the emissions test. I believe in the USA the emissions test is known as the 'smog test'?

If you have a problem with excess CO emissions on a car the cause is often an incorrect fuel/air mixture or a faulty sensor called the lambda/oxygen sensor in the exhaust system

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1986 NISSAN 300ZX FAILED EMISSIONS HIGH CO


I would replace CATalitic converter, this car is old, plus a tuneup is 100% necessary , spark plugs wires, ditributor cap & rotor, plus both the air & fuel filters need replaced. change oil & filter. then you will pass emissions test. and your car will run like its suppose too. if you don't do all this , then buy a new car !

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The co level is to high, the car has been standing for 9 months


High CO results from a vehicle running 'naturally' rich - ie a rich condition that is not being forced from the computer.

The basic, most probable causes of a high CO count could be one of the following;

High fuel pressure (constricted filter, pinched line, etc)
Ruptured pressure regulator diaphragm
Malfunctioning Evaporative Emissions System
Crankcase fuel contamination (head gaskets, injector/regulator leak)
Closed loop incorrectly shifted to rich (o2 sensor, map/maf sensor, coolant temp sensor, Throttle position sensor, etc, etc)

Tell me...What is the NoX Reading?

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Not sure, but did you replace the oxygen sensors. Is your catalytic converter still good?

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Emissions failing due to high nox


NOx emissions are the result of high combustion chamber temps pure and simple. NOx readings go up whenever there are hot spots that exceed about 2400 degrees. Things like lean mixtures contribute to high chamber temps, as does over-advanced ignition timing.Lean mixtures are usually caused by some failed components or by air (vacuum) leaks in the intake.
Poor fuel quality contributes to detonation, another cause of high chamber temps.
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  2. Try a full tank of high octane fuel(run at least half a tank through before testing)
  3. Have the tester do the rolling tests with the trans locked in first gear.
  4. Make sure the oxygen sensors is working.
If you have done all of this and still fail, You will need a new catalyst

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High CO usualy means the O2 sensors are not reading properly. Take it to a parts store that can read codes, I know Auto Zone does in my area. If it is the O2 sensor it is an easy fix but the sensors run about $50.00 each.

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