Need help with P0420 code

[dobie]

I have a 98 Firebird 3.8L V6 5sp that's throwing a p0420 "catalyst efficiency below threshold bank 1".

The car is stock with the exception of a Flowmaster catback system 2.5" pipe dual exhaust. Has 90K miles with the original cat. I have emissions inspection and they do a visual as well as OBD check so 02 simulators are out of the question.

I've changed the driver's side O2 sensor, wires, changed from 21 to 19lb fuel injectors (the car had supercharger on it at one time).

I'm thinking it's time to change the cat but I also thought it could be the exhaust flows too well and putting a stock muffler could help. If it is the cat then why am I only getting the code for bank 1? I'm getting tired of throwing money at this problem which is why I'm here. I'm looking at welding in a generic cat ($72) instead of an OEM replacement ($330). Do you think this will take care of the code? Should I be thinking new muffler? Any help would be appreciated.

Thanks

[iGoRa]

Re: Need help with P0420 code

p0420 = new cat inv. /end of problems. Generic - depends on your local rules. get 3" or 3"to 2.5"

If it is the cat then why am I only getting the code for bank 1?

How many cat invertors your car have?

I've changed the driver's side O2 sensor, wires, changed from 21 to 19lb fuel injectors (the car had supercharger on it at one time).

this is stupid .
22# are stock on 98. Put them back! you dont know with what you are messing with. You cant just put different size of inj and expect the car working without tune.

[dobie]

Re: Need help with P0420 code

How many cat invertors your car have?
Just 1 which is why I would expect to see the the same code for bank 2 since they share the converter and downstream O2 sensor.


this is stupid .
22# are stock on 98. Put them back! you dont know with what you are messing with. You cant just put different size of inj and expect the car working without tune.

Everything I've read says that 19# is stock on a 99 which is why I put them on.

[iGoRa]

Re: Need help with P0420 code

How many cat invertors your car have?
Just 1 which is why I would expect to see the the same code for bank 2 since they share the converter and downstream O2 sensor.

error code for bank 2 is disabled in pcm as well as wiring for it is not present in v6

Everything I've read says that 19# is stock on a 99 which is why I put them on.

what year is your car? 99 or 98? It does not matter, they are 22# stock on all 98-02 for sure. I think 19#ers are for 3.4

edit: 22.18# to be precise.

[dobie]

Re: Need help with P0420 code

error code for bank 2 is disabled in pcm as well as wiring for it is not present in v6

That makes a lot of sense, Thanks

what year is your car? 99 or 98? It does not matter, they are 22# stock on all 98-02 for sure. I think 19#ers are for 3.4

edit: 22.18# to be precise.

The car is a 99, I typoed the original request. What are you using for a reference? I'm using Alldata but sometime I wonder if it's correct.