The car first off is a 2005 Sports Edition Automatic with 4 Gears. I just hit 64k miles on it and replaced all 4 spark plugs and ignition coils at 60k. The car has a error code of the Catalytic Converter, I don't remember the exact code but the guy at Advance told me it was the O2 sensor for the Catalytic that most likely went bad.

I question it is the O2 senor because a month back I decided to take the car out to see what I can top it off at (The Cat error only happened about a week ago and may be unrelated). At 4th gear around 5000 RPMs it took around 3 minutes to climb from 97 MPH to 101 MPH where the car just sat there and and RPM never exceeded 5000.

At first I thought it was a the governor, but it suppose to stop at around 120 MPH. So now I am left with a dilemma which I can't figure out. I have a few thoughts of what is going.

*The Cat may be clogged giving off the error code causing the car not to go past 101 MPH.

*The Cat is fine and it's really the O2 sensor bad but what is causing the car not to go past 101 MPH.

 

If it is a gradual "soft" limiting, which it sounds like for 3 minutes to gain 4mph, then i bet it is a clogging cat, which is capping flow. Doing those hard pulls with a clogged cat is dangerous... i wouldn't recommend it.

Over time, that cap will continue to drop, until you can't even get to 60mph at full throttle. By the time you reach that point, you are already WELL into the range that you can/will damage the engine, both O2 sensors, and are risking a car fire.

 

3 minutes? Where do you have time to go 100 for 3 minutes without getting busted lol. I need to come take some runs by you. Around here there's not a highway without a cop around..

I had a friend that also had this issue. We swapped his cat for a Midpipe and the problem vanished. Hopefully this is the case for you as well.

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