il pirata

I remember the days in CA dealing with the DMV...just went for a smog check on the 96 C4S in the Denver area, they hooked up the ODB to the computer and that's it, 5 minutes and $25.

TheBen

Things just don't wear out by mileage, they also wear out over time. Our cars are get on over 20 years old now.

CorrdoBrit

Maybe rubber bits and seals but I don't think this would apply to a catalytic converter. Plus this problem goes back at least 8 years from what the OP says

Sunrader

AZ Targa, I'll ask my mechanic if I can go on the roof and take some pics for you. He has 2 heavy duty hoses hanging from the ceiling that connect the car exhaust to the roof filtration system It's probably an electrostatic precipitator.

pp000830

Your problem is a Failed CA state government as in their failure to reign in the unaccountable California Air Resource Board who creates regulation via fiat designed to aggravate the car owning public. Unfortunately it is much easier to swap out catalytic converters than swap out the CARB.

autobonrun

You mentioned the max is 430 ppm. I would want to know what similar 993's that pass the test see. This would tell you the magnitude of your problem. I think I would run some Techron through as well. Then I would find a track where I could legally run the car hard. I'm thinking some of the carbon dislodged would end up traped in the cat. I'd want to really heat them up and attempt to burn that off. With all these additives/dilutents, I'd also do an oil change afterward.

Sunrader

Good point....I'd like to hear from other California drivers to find out what their measured 15mph NOx levels are. I plan on doing another "Seafoam" treatment & oil change before my next smog test. I don't use any fuel additives, my mechanic injected the Seafoam into the intake manifold via a vacuum line and let it soak for about 15 minutes before starting the engine running it out. Like I said in my earlier post, I've tried the "running it hard" technique but apparently it wasn't enough because not only did I fail upon retest, I was actually higher. There seems to be a fine line between getting it hot enough to turn on the cat (800F) and getting it too hot to increase NOx. For mine, I can get the cat to operating temp after approx 15-20 minutes of running at highway speeds.

SimonM_98

I had to smog mine last month. Car has around 90k miles.

NOx at 15mph was 32ppm
NOx at 25mph was 48ppm

CorrdoBrit

Last emissions test at 34K miles was 5ppm (NOx; 15mph). Standard in TX for a '95 car is 937ppm.

71-3.0-911

Here is mine. Measurement is peak for entire test. 96 w/ 101k no rebuild that I am aware of.

Kika

Taken in August 2016, top end just done.

idle. 8ppm
2500rpm. 16 ppm

nine9six

2016 smog readings @ 73k mi., no top end rebuild.

Idle: 13 ppm
2500 RPM: 9 ppm

Spyerx

Post pictures of alll your failed printouts for this years tests.

AllMine

Just my thoughts with years of 4 gas analyzers. Late 80's tech at the time though. To tell if a cat is weak, or failed, a repeated tapping of the throttle on a hit car should not result in much over 800ppm HC emissions. If the scale gets pegged out (over 2000PPM HC's ) then the cat was surely toast. NOx forms under high cylinder pressure with combustion temps over 1500 degrees. An increase in compression would surely raise NOx readings... carbon build up would be the cause. Timing over advanced will also cause it. The last thing to try would be a track day to clear out the carbon, unless you wanted to add some type of acohol/water injection system for a while... that will surely remove carbon from the chamber... but yes, the cats are not really designed to remove NOx in our older cars, some yes, but a lot, no.
Old tech would have a air injection line running to the middle of the cats for NOx reduction, and or a EGR valve.
Spark knock, or pre-ignition will spike NOx heavily as well. 15 MPH with a light load will result in high spark advance, leanish conditions, and a tendency to raise combustion pressures.
Curt