Hello Guess,
Looks more like a high CO problem to me specially since you mention the bad fuel economy. There is the possibility of a rich fuel mixture. The diagnosis for this failure should include close inspection of your vehicle's fuel management and control systems. Check out
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I got most of this info from them.
CO stands for Carbon Monoxide. It is a by-product of incomplete combustion, more then often related to the presentation of too much fuel to the combustion chambers. The spark created at the sparkplug can only burn a small amount of fuel, the fuel it cannot burn is sent out the tailpipe and will normally contain high levels of partially burned fuel(CO) and raw fuel(HC). In a "Rich Fuel" condition diagnosis would begin with inspecting all possible mechanical faults, which could cause excessive fuel to enter the combustion chambers. This diagnosis would include inspecting your vehicle for high fuel pressure, intake vacuum leaks, air restrictions and/or leaking fuel injectors. NOTE: A dirty air filter may restrict ample air from entering the combustion chambers. The lack of air will create a rich fuel condition and result in high CO. If your vehicle has not had a tune-up in the last 15,000 miles, we recommend a quick service from a local smog stations.
As part of the mechanical system diagnosis, the vehicle's EVAP system would be inspected also. The EVAP system is designed to introduce gas tank and/or carburetor fuel bowl fumes into the combustion chambers. These gases (vapors) are just as combustible as the actual fuel in your gas tank. If they are not routed into the combustion chamber, the vapors build up within your engine's fuel system and eventual escape through a vent into the atmosphere. So in-order to eliminate this problem auto manufactures have designed the EVAP system to make use of this vapor. If your EVAP system is not functioning properly it can present these vapors to the combustion chamber at the wrong time and/or to often, causing a rich fuel mixture and increased CO in the exhaust.
Once the mechanical faults have been factored out, the focus would turn to the vehicle's electronic fuel control system.
Fuel distribution to your engine's combustion chambers is controlled by your vehicle's ECU(Engine Control Unit) and fuel injectors. In order for your engine to pass a smog inspection, fuel delivery must be preciously controlled to produce the least emissions. If the injectors do not present enough fuel to the combustion chambers, this would cause low CO emissions. In a situation where the injectors present too much fuel, this would causes high CO emissions. In order for the ECU to estimate the right amount of fuel to distribute, it needs to know how much fuel is currently in the system. This way it can always maintain a proper Air/Fuel ratio and keep emission levels at their lowest. The main component responsible for letting the computer know how much fuel is in the exhaust system at this moment, is the Oxygen Sensor. The Oxygen Sensor sends an electrical signal to the ECU, letting the computer determine exactly how much fuel it should continue to deliver to the combustion chambers. If for any reason the 02 sensor (oxygen sensor) does not send accurate information to the computer or it is "lazy" in sending the correct signals, the fuel delivery program can be altered. The computer may then present either too much or not enough fuel to the combustion chambers and therefore cause an emission failure.
In a computer controlled engine such as this, there are several components which also play a role in determining Air/Fuel ratio also. Along with the Oxygen Sensor, components such as the, TPS (Throttle Position Sensor), ECT (Engine Coolant Temperature Sensor) and the MAP (Manifold Absolute Pressure Sensor) sensors also send vital engine information to the computer which is used to determine proper air to fuel ratio. If any one of these components are defective they can alter the fuel delivery program. A smog service station can diagnose each component and report it's condition.
I suggest checking out
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They have great info onsmog failures.
Alec - The Smog Tech