Elephant! from typical diagnosis procedures:
AUTO REPAIR HELP - DIAGNOSE - EMISSIONS TEST FAILURE
If you have high HC AND CO, then the cat is suspect, but it is pretty low on the list of suspects. Your CO is nowhere near high in any of the tests.
High HC by itself looks like ignition mostly suspect, and then vacuum leaks.
Note, you had a
HUGE spike in NOX in the third test also, like EGR went wonky or something.
You could have several things going on, emissions are not simple to diagnose, don't pretend that they are.
Quote:
DIAGNOSIS
Diagnosis of high emissions can be an involved process that usually requires special tools and measuring equipment. However, armed with a test report indicating what gases are high can help you determine what systems may not be functional. If the vehicle has failed as a result of high CO and HC, the CO failure should be diagnosed first. If the "Service Engine Soon" or "Check Engine" light is on it should be diagnosed prior to any emissions diagnosis. CO Failure is the result of an excessively rich air fuel mixture. The following is a list of the most common causes:
- Defective Oxygen Sensor
- Inoperative Air Injection System (if equipped)
- Leaking or defective Fuel Injectors
- Restricted air filter (especially if high CO is present only at high RPM)
- Vacuum leaks resulting in improper MAP sensor operation
- Defective air mass or air flow sensor
- Malfunctioning fuel evaporation system or purge valve
- Defective Catalytic Converter
- Defective thermostat (cooling system), thermostat stuck open
- Oil contaminated with fuel, excessive miles between oil changes
HC Failure is the result of incomplete combustion. Any item that causes incomplete combustion can result in high HC. The most common causes are:
- Worn spark plugs
- Defective spark plug wires
- Worn distributor cap and/or rotor
- Improper ignition timing, usually over advanced
- Vacuum leaks
- Engine mechanical failure, low compression, worn valves, excessive oil consumption
NOX Failure is the result of combustion temperatures that are too high. The most common causes are:
- Inoperative Exhaust Gas Recirculation System (EGR)
- Cooling system malfunction, engine running too hot (restricted radiator, defective thermostat, etc.)
- Over advanced ignition timing
- Excessively lean air fuel mixture (defective oxygen sensor, MAP sensor or Air Mass Sensor)
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I'm reminded of how many folks would replace the carb when the carb isn't even the problem.