Originally Posted by hondarocket

Actually you should see an increase n hp/tq not a lot but some. The cat restricts flow. So if the honeycombs are gone it will be less restrictive. You may not get an error unless your car has an o2 sensor after the cat. If that is the case then you may see some drop off in power because the sensor is readings will be off and interfere with air/ fuel mixture which the ecm uses to the readings from the o2 sensors to set.

try this.

find the 02 sensor after the cat if there is one. if not then find the one before the cat. remove it form the exhaust gently if possibly try not to bang it. Get an empty 20 ounce soda bottle. Put the sensor in the bottle and tuck the bottle up in to the chassis somewhere and secure it with a zip tie. plug the whole in the exhaust with the appropriate sized bolt.

This modification will trick the ecm in to believing the exhaust is always putting out fresh air and will increase the amount of fuel.

1 this is probably not legal on road and should be used for off road use only like at the track

2 secondly your mpg will go down

3 you will see an increase in hp at wot because you have richened th air/fuel mixture. this set up is great with turbo/superchargers CAI and a good cat back exhaust or headers. this is not meant for a daily driver.


now back to your original question. if the cat is bad and you have a sensor after the cat yes you will see a decrease in performance and possibly mpg.

if you don't have one after then I would say you might have a bad o2 sensor but you should be getting some sort of a code. if you are getting a code the chances are it is something that might not direct you toward the 02 sensor but like emissions or plug misfiring or Something like that. but check the 02 sensor first they are much cheaper than a cat and easier to replace.

what are the symptoms the car has been showing?

that will greatly help in the diagnosis.

the issue you mentioned with the tranny is more likely the engine running crappy if the 02 sensor is bad or the cat is bad. these 2 items really dont directly affect the tranny but may affect performance which might appear to be the tranny. If the tranny is bad then you have a different problem than the cat.

I hope this helps. post all the sysmptoms maybe we can help


hondarocket