88 MJ Comanche failed CA smog high CO - JeepForum.com
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post #1 of 2 Old 08-10-2013, 02:12 PM Thread Starter
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Location: san luis obispo
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88 MJ Comanche failed CA smog high CO

88 Comanche 4.0 i6 just failed smog for torn PCV line, torn evap line and high CO. Acceptable CO levels are under 1.00% @ idle and @ 2500 rpm. My MJ scored 2.08% @ idle and 1.59% @ 2500 rpm. Any suggestions? I was thinking about replacing only the O2 sensor MAP sensor and spark plugs. Could I possibly pass by only replacing the torn PCV and evap lines?

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post #2 of 2 Old 08-19-2013, 08:27 AM
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1984 XJ Cherokee 
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Location: acworth
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HC: Unburned Gasoline
CO: Partially Burned Gasoline
CO2: Completely Burned Gasoline
O2: Oxygen, the Good Stuff
NOx: Oxides of Nitrogen (This is only seen by a 5-gas smog machine)

HC: misfire or bad burn
CO: too rich
CO2: engine efficiency
O2: too lean or just air
NOx: too hot or too lean

High CO means you are running too rich to pass. That means you need to lean it out a bit, which could be done by replacing the O2 sensor, etc. Did you have them run it in 'test mode' to check it before the actual run? That tells you all the numbers above, but doesn't 'cost' you to run it (most shops will run it in test mode if you ask them). Then, you look at what it fails on, make a quick adjustment, run test mode again, and if it passes in test mode, you have them run it for real and it'll pass.
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