Hello all,

I've done some searching but still can't find an answer.
I have a 2000 Civic EX (Stock d16y8/156,XXX) which is throwing a p0420 code.
"Catalyst System Efficiency Below Threshold (Bank 1)"

I went to Autozone for a print out and they told me this could mean:

1.Air/Fuel Ratio concern
2.Air leak near h20s (heated oxygen sensor) bank 1
3.Ignition system concern
4.faulty catalytic converter

The original exhaust setup I bought the car with didn't have a catalytic converter and was just welding straight through with a place for the secondary 02 sensor.

I bought a used exhaust system off a 96 civic ex, which included a 'hollowed' out catalytic converter all the way to the muffler. (not stock, bigger pipping but somewhat stock look?)

I installed the the cat, straight pipe and S pipe and used my stock muffler and re-set the CEL, but after driving 5 miles, the CEL came back on and threw the came p0420 code.

I also tried putting my hand over the muffler (with a rag, of course) to see if I could find an exhaust leak, but didn't see anything.

Also, while driving, I do smell gasoline.
I know that like 99% of the time p0420 is either a bad cat or an exhaust leak (as per RonJ), so what should I do from here?

Is changing all the gaskets in the exhaust something I need to do?


Sorry for the long post, and thanks in advance.


EDIT: I live in New York, and due the CEL I can't pass inspection and my inspection expired on 7/18

 

do you have a 02 sensor up front? before the cat.....

and a hollowed out cat would throw a code...more then likely.

You could try the defouler trick on the 2nd 02 sensor...to fool the ecu- a defouler at autozone is 3 bucks, and a cat is going to be a considerable amount more.

 

P0420 almost always indicates a bad cat, though it can also be thrown by an exahust leak.

 

Yes I have both 02 sensors, upstream and downstream.

I've been looking for the DIY, but can't seem to find it. I came across it a while back...

I'm trying to find a temporary fix, just to pass inspection.
Once I'm not on a tight budget I will replace the full exhaust, but can't do that yet.

 

See bold, you need a cat that actually works not a pipe, not a "hollowed" out cat, but a cat that has the insides intact and functioning. /thread

EDIT You can try to use a spark plug fouler (like $5 from autozone) and trick it and see if that works for a temp fix
http://forums.evolutionm.net/evo-how...ouler-how.html

 

I've heard that you can pour lacquer thinner into your gas tank to clean the cat, or to leave it in soap over night?

When I installed the new cat to the downpipe, it wasn't flush. Does this make a difference? One of the bolts is loose due to the fact I was taking it off again today.



Would doing the spark plug fouler trick remove the CEL?

 

You just said you have a hollowed cat which means there's nothing to clean. You need to either get a cat that has the insides intact, try the fouler, or get an O2 simulator. The fouler is the cheapest option to try, you need to do it on the O2 after the cat not the O2 before

 

I'm going to try the fouler option tomorrow and see if it helps any.
Whats the purpose of the 02 simulator?

Also, are the aftermarket catalytic converters okay to have? I've read mixed reviews.

 

If A/F ratio is also a possibility, could that mean I need to replace first o2 Sensor, or that would be a separate code?

How would I know if I have any other codes besides this one? It would show up on the scanner, right?

 

Separate code for the primary O2. Any other codes should show up. Just make sure when you use the fouler to reset the code and see if it comes back. The secondary O2 just let the ECU know if the cat is working or not which in your case is not. There are mixed reviews but a lot of people go with Magnaflow.

 

DO you have any idea what the cat does OP? it seems like you are ignoring every saying you need a new Cat! Since yours is hollowed out your 2nd O2 is seeing that the Cat isnt converting your exhaust and throwing up a code.

 

If your cat is hollowed out there is no platinum to help make the emissions more Eco friendly. the 02 sensor(s) are compared before and after the cat converter To measure its efficency. If it is hollow it.will not clean the emissions. The ecu will see there is no differnce before and after the cat (hence the upstream and downstream) and will throw a code. Get an 02 fowler or a proper catalytic converter.

/thread.

 

I didnt understand what a cat did, and now I do.
I've been saying i dont have the $ right now for a cat and was looking for alternatives to

I got the foulers in today and i'm hoping the light doesnt come back on