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Everything you need to know about Catalytic Converters.
Discount Converters LTD.
6823 Fulton St.
Houston, Texas 77022
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What causes High NOX Emissions
Thousands of technicians have faced the challenge of bringing a particularly stubborn application into compliance for NOx emissions. High NOx readings are a clear sign of performance issues somewhere in the system. The question is, where?
Among the potential causes of non-compliant NOx readings are:
Misfire condition Malfunctioning or improperly adjusted EGR valve Failed oxygen sensor Leak in exhaust tubing upstream of converter Excessive carbon deposits in combustion chamber Improper spark advance Blocked coolant passage Overly lean air-fuel mixture Damaged cold air duct Failed or malfunctioning catalytic converter Corroded or damaged engine sensor electrical connections
Please note that while a failed catalytic converter will contribute to high NOx readings, the failure in itself may have been caused by some other upstream performance problem. In all cases, it is crucial to identify the root cause of the problem before blaming the converter.
Case Study " I'm working on a 1992 3.1-liter Chevrolet that failed in the test lane. The results were very good for HC and CO—nearly zero—but it failed for NOx. The converter seems to be operating properly and the engine is running okay. What's causing the problem?"
Answer: Because this application, like many others, does not have an EGR adjustment, there's little the technician can do to "tweak" the engine's performance to bring it into compliance. It's clear the engine is running overly lean. A lean engine operating condition produces more NOx than usual, and the lean exhaust chemically interferes with the converter's ability to clean NOx (remember that excess oxygen is good for cleaning HC and CO, but bad for NOx).
There are dozens of potential causes of the high NOx readings, ranging from the relatively easy (detonation or failed oxygen sensor) to the extremely difficult and time-intensive (an improperly signaling MAP sensor). Because the engine is otherwise performing satisfactorily, the least expensive option may be to upgrade to a heavier duty converter such as a CleanAir "Premium" unit featuring increased catalyst for greater efficiency.