So my 1999 RS threw a CEL the other day, and then I noticed that I am definitely not running right. The CEL is P0420 which is "Catalyst Efficiency Below Threshold (Bank 1)."

Never had this problem that I know of and was wondering if anyone else has. I am pretty much stock with an intake and headers. I noticed that when I start the car, the RPMs jump to between 1500-2000 and then after a few minutes finally head back down to like the 500 RPM idle range. I am also having heavy hesitation in every gear between 3k and 4k RPMs but nowhere else ouside of that range. I will be fine getting up to 3k... will hit hesitation hard (the car stutters and I can tell there is obviously a problem)... but then when I hit 4k, the car gives a little kick and I am at full power. I just wanted to get some opinions before I take her to get looked at seeing as how I don't have the time to wait around at a dealership for hours on end. It would also be nice to be able to get any parts before I have it replaced so I don't have to spend a grand to fix a $200 problem.

I changed the plugs and wires about a year ago so I don't think that is the problem, but somebody said that the coil pack may be causing a misfire

Could it be the catalytic converter?

I have also been told that at times headers will throw this CEL b/c it throws off the O2 sensor, but I have had the headers for about a year now and this is the first time it has thrown the CEL and the first time that I've had the hesitation.
Thanks for any help guys

 

 

Don't worry about it, because with a modded car, you will get all kinds of things like that. I get the p0420 code all the time.

 

I'm not worried so much about the CEL, I have had a constant CEL for about the past 2 years , until they cleared it when my car was in for clutch work at Mastro, the thing I'm worried about is the hesitation between 3 and 4K RPM. If I could get that squared away, I wouldn't worry too much about the CEL, it would be all good. It is just really annoying hitting 3k and just having your car lose like 30% power while stuttering (and it's not like I'm losing 30% of 300 ponies, where I would still be pretty quick, I'm losing 30% of my stock 165 or some analogy between a fast car and my slow car)

 

that code is from the exhaust

 

I have not. How does it work? How much will it cost me? Can I do it myself with simple tools? Will it counteract the hesitation problem?

Thanks for the suggestions,
-Sean

 

Buy 2 spark plug non foulers from auto zone. Drill one out and attach them together. After that you screw the combo into your O2 bung and your O2 sensor in the other end. It makes it so your O2 sensor is far enough out of the direct exhaust stream so you won't throw a code. It only cost me like $5 and I have never thrown a code. Or you could buy a electrical fix from Mastro or PonyExpress and solder into your O2 sensor wiring. I had this on my last WRX and it worked just as well. It's like $25 though.

 

your stock catback is still on the car, correct? Sounds to me like your cat might be clogged, causing the stutter and powerloss. The code itself shouldnt be the problem, so the CEL fix will do nothing but clear the light.