[tshih]

Sam,

It is a great suggestion which I considered as well. One would think that the OBD2 system would have thrown a code for bad O2 sensor if that was the problem. I'd assume that the values of the readout for the post catalytic sensor is not what's expected from the pre-cat O2 sensor. Because ethanol is present in excess and that leans out the mixture being burned in the engine, the cat is working but the values are not what it's preprogrammed mapping expects.

I have a broad band O2 sensor in the form of a LM-1 from Innovate Motorsports which allows me to measure the exhaust for air-fuel ratios. I suppose I can take readings before and after I do a tuneup and after I change the O2 sensors.