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Old 10-18-2001, 12:20 PM
Telerding Telerding is offline
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Join Date: Aug 2001
Location: Santa Maria, CA
Posts: 49
O2 Sensor and Catalytic Converters

A number of members of this forum have talked about removing the "Pre-Cats" (called Primary Cats in the manual) from their exhaust systems to achieve better performance. I believe the theory is less exhaust restrictions.

My question is:

Given that the O2 sensor is usually placed AFTER the Pre-Cats, what will this do to the resulting fuel mixture (lean/rich)?

The O2 sensor will now see exhaust gasses that are much higher in CO, Oxides of nitrogen and unburned hydrocarbons. This will also result in a higher concentration of Oxygen than would have been seen post-catalyst.

I believe this will make the Lambda control system set an operating point that is richer.

One corroborating piece of evidence is that one of the forum members burned his secondary catalytic converter out after removal of the pre-cats.

Thanks for any of your expert opinion.

Tom Elerding
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