Failed smog due to high HC and NO emissions...help!

[jkarolyi]

Hi All,

I had gotten a weird P0420 code "Catalyst System Efficiency below Threshold - Bank No 1". when I was driving my new-to-me '96 993 home. Check out this thread:

http://forums.rennlist.com/rennforum...&highlight=Jay

I reset the CEL, but it came back after about 50 miles. I reset it again and drove it around for a good 100 miles and it didn't come back on. So I took it directly to the smog referee station since the readiness codes were not set and I know this is an automatic fail. The referee said he would have passed it with readiness codes not set, but my emissions were too high. Here's my result:

HC MAX AVE MEA
15mph 54 9 87
25mph 37 7 41

CO MAX AVE MEAS
15mph .50 .02 .10
25mph .47 .03 .05

NO MAX AVE MEAS
15mph 430 57 471
25mph 717 50 419


CO2 is not the problem, so I'm assuming the cats are good. Where would you start to track down the problem? Am I running rich or lean? Would the O2 sensors cause this?

I searched through the service records and found out the plugs haven't been changed since the 30,000 mile service! It has 83,000 miles right now, and I'm assuming it still has the original plug wires too. Caps and rotors were changed last year. One thing I noticed when the car was under load on the dyno is that a *little* blue smoke puffed out of the tailpipe. Not a lot, but it was noticeable. Car has had oil changes every 3-5,000 miles with Mobil 1 15W-50.

Here's my plan:

1. Change the oil and filters and replace the Mobil 1 with 20W50 Castrol non-synthetic oil. I had a '89 Carrera 3.2 with 150,000 miles (never had a top end done!) before this...never any trouble with oil burnoff using Castrol dino.

2. Change the spark plugs and plug wires. I read the DIY on p-car.com and it says to buy "STI" brand plug wires. Where can I buy these? The stock Beru ones are $500+ :crying:

3. Go back to smog referee (re-tests are free!). If it fails again, I will start testing and replacing 02 sensors.

Think this might be enough to do the trick? This will be my first DIY 993 project, although I did just about everything to my old '89 3.2 Carrera.