He said to leave the cats in. He did not say to leave the O≤ sensors plugged. Disconnect them.
"You probably already know that a catalytic converter is a piece of
Cats are required because aside from carbon dioxide (CO2) and water (H2O), your engine produces hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx). The theory behind a catalytic converter is to get hot exhaust gases to pass over a surface that has been coated with rhodium, platinum and/or palladium. These metals are known as the catalyst material. When the exhaust enters a catalytic converter, it cannot leave without coming into contact with the catalyst material. The chemical reaction between the precious metals and the hot exhaust results in a slightly less poisonous gas than what initially left the exhaust port.
Now that you have a basic understanding of how a catalytic converter works, how does it wear out? In a perfect world, the cat's internal temperature will be about 1200 degrees, the air fuel ratios are correct, and the cat will work forever. There are no moving parts, and the catalyst material doesn't get burned up in the chemical reaction, so what could possibly go wrong? Plenty. I've explained what happens in a best-case scenario. Over the life of a car, a number of things can cause a converter to fail. Usually, catalytic converters fail because either the engine has been running too rich
, physical damage, or exhaust contamination."
From what I've read, max power is gained by running slightly richer than stoich. I've also read that pretty much all FI systems are set to allow the engines to run rich during such throttle applications whether or not you have sensors. It's at lower thottle openings i.e. "normal" applications that the sensors are maximizing your mileage by using the oxygen feedback to optimize the a/f.
This use of feedback also comes in handy for dialing in proper a/f due to differences in oxygen based on altitude/temperature.
I ran my XR with the sensors disconnected and reconnected and I can't tell a difference performance, but the gas mileage seems to be worse without them.
Given that over time, the richer condition from running without the sensors may damage the cats, I couldn't think of a good reason not to plug them back in, so I did.
FWIW, I have had the sensors removed on my FJR for many tens of thousands of miles and I don't seem to have any issues with it. I did it because that was the configuration recommended by the PCIII mfg for the map I am using. As far as I know, that isn't the case for the Cross bike Stage 1 set up.