Can someone take a look at my attachments of my O2 sensor and Cat data?
One test at a time, I'm trying to systematically find a problem leading to my drastic loss in mpg and eliminate the fact that its all in my gearing.

I had to delee a chunk of the temp data just to shrink the file size but hopefully it will give a good idea of what going on.

Attached Files

	cat temp.doc (131.5 KB, 17 views)
	O2's.doc (107.5 KB, 21 views)

Hi.

Correct o2 sensor (post cat) function is pretty simple. The engine starts and begins to warm the cats, this causes an increase in voltage from .055V to a nominal .7V when fully warmed. After 60 seconds, the system goes into closed loop where the PCM spikes the fuel injector pulse width up and down to do 2 things. First, the stoichiometric ratio or lambda is modeled with the pre-cat sensor to provide rich/lean readings. Second, the changes in unburnt fuel through the system are measured by the post cat o2 sensor. These changes in fuel are not supposed to create drastic voltage changes on the o2 sensor due to the catalyst simply absorbing the extra oxygen. If the changes in o2 sensor readings match the changes in IPW the system will trip the catalyst efficiency obd2 code. Note that the o2 sensor changes are detected using PLL and not a lookup table - enabling phase transitions to appear like the cat is working (o2 sensor simulator).

If your cat is simply failing (or on the edge of failing), the PCM will retard the timing to burn extra o2 to keep the post-cat o2 sensor happy. Eventually, this will have no effect and the P0420/P0430 codes will be tripped. A way to "fix" it is to put on 2 spark plug defoulers to move the sensor nose out of the way of the exhaust stream. This does not improve mpg or hp. A better way is to put a small catalytic converter on the nose of only the o2 sensor to provide the PCM with data that shows that a brand new cat has been installed and advances the timing accordingly.

It looks like the mini-cat is what you are looking for. PM me for details.

Thanks for that great info man. This made perfect sense. Going over my data and with further research it looks like I’m an acceptable range. While my spark plugs are only 15k miles old, it may be time to pull and read them to make sure I’m not too rich.

Make sure your plugs are gapped correctly. It should be 0.043”. Mine came gapped at 0.37” and I had to reset them. A small gap will not give you a hot enough spark.