Rep Power: 0

Hi, I recently bought a 2002 Civic ex (no Vtec).
A little while later I started to notice several things, including high fuel consumption, barely 5.2MPG (city)
I already did it following

1. Replace thermostat (It reaches temperature in just a few minutes.).
2. Replace PCV valve
3. Replace IAC valve (it was damaged and wouldn't open)
4. Change spark plugs
5. Clean injectors

Yesterday I took a long road trip of about 50km -- 31 miles and got about 12MPG. I often noticed a lack of power, especially on uphill's, and the check engine light came on (P0420 - low efficiency of the catalytic converter). At the end of the trip, I noticed that I could touch the exhaust as soon as it was hot as a cup of coffee.
This makes me understand that the catalytic converter must be clogged and this is causing the high fuel consumption and lack of power. In this case, is there any way to easily fix it, even if it is temporary?
Some of the obd2 scanner values ​​are as follows All values ​​are at idle after about 20 minutes on.

1. Intake manifold absolute pressure (42.0 kPa)
2. Calculated load value (41.2%)
3. Engine coolant temperature (87 Celsius)
4. Ignition timing advance for cylinder 1 (5.0 to 7.5)
5. Oxygen sensor B1-S1 output voltage (oscillates rapidly 0.250 to 740)
6. Oxygen sensor B1-S2 output voltage (oscillates slowly between 0.095 to 0.475)
   
   (update)
   I checked the upper oxygen sensor and noticed there is no catalytic converter inside.

 
Rep Power: 223

Are you in the US? EX trim is supposed to have VTEC here. You used MPG but also Celsius so I'm not sure. I'm mostly curious because with VTEC the cat is underneath the car, not in the header.

 
Rep Power: 0

I'm from the Dominican Republic, here we use (gallons, celius and km), I converted the kilometers to miles because I know that most people on the forum are from the USA

The engine doesn't have a VTEC and the catalytic converter is in the exhaust manifold.

I suppose that in the Latin market they come with inferior features. Although I wouldn't be surprised if they changed the EX letters on the back. The truth is I wouldn't know how to differentiate it since I don't have much knowledge or anyone close to me who understands much about the subject.

 
Rep Power: 223

Just trying to get an understanding. The Canada trims were similar. EX didn't have VTEC. US EX was similar to CAN Si. US Si was similar to CAN Si-R. It's all the same, just different names.

12 MPG is terrible, as you know. A hollowed out or missing cat won't affect MPG. The primary oxygen sensor controls fueling so it could be failing. I'm not familiar enough with the readings to know. Are you able to view the fuel trims? Long/short fuel trim are how much fuel the ECU is adding/subtracting based on sensors. If the primary oxygen sensor were failing, I'd expecting both to be showing adding a bunch of fuel.

This could be something simple, like a dragging brake caliper.

 
Rep Power: 366

to find out if cat is clogged or not, just drive it without the o2 sensor. If it gets better, then it is clogged.

 
Rep Power: 366

primary o2 sensor on the way out also causes low mileage.
also, better use OEM sensors, honda picky on aftermarket sensors, they soon do not work