I failed smog three times....I got the hot cam kit, mid headers, a high flow cat and PCMforless tuning. I was at 118 (15mph) and 86 (25mph) on the HC test. Changing my 02s passed the first and brought the second down to 49. Max is 48. I tried the CNC "Guaranteed to Pass" fluid and my HCs went up from 49 to 52.

My thoughts are that my Carsound(Magnaflow) hi-flow cat may be the problem. A while back my header bolts backed out on me and I drove for several months before I got that problem fixed. I heard that my cat may have melted inside as a result thus messing up my smog. Could this be a possibility? Would a new cat get it down those few points?

Thanks

 

Remember a cat works better the hotter it is.

Try a little bit of alcohol in the gas.

Make sure there are absolutely no more header leaks.

High HC means you are running rich so maybe try cleaning out your MAF sensor OR if try unplugging the MAF sensor and running SD. Id say replace your O2 sensors but you already tried that.

 

What do you mean, "running SD"?

Could the exhaust leak from the headers have effected the inside of the cat?

 

If you've got the 160 thermo, tweak your fans so they don't come on until 210 or higher. Set your idle speed right at max allowable. Pull a bunch of timing from the idle to the high rpm limit of the test; set a max of about 15 degrees advance. Run the tank down to 1/4 and dump a gallon of methyl hydrate in.

I did all of the above and passed just last year with the original cat on my '95 with hotcam etc.

if that doesn't work, you may have to consider a new cat.

 

What does methyl hydrate do? Where can it be purchased?

Just curious -- no emissions tests in Michigan!

 

Methyl Hydrate is a type of alcohol - some gas line anti-freezes are methyl hydrate some are isopropyl alcohol . . . you should be able to purchase it at auto parts stores or hardware stores

The garage where I used to work in high school carried it - in small bottles and 4 litre (aprox 1 US Gallon) jugs

Can't tell you how it helps with the smog test though

 

My buddy's LT1 had highflow cats and didn't pass. Swapped the factory cats back in and passed.
I left my Cats alone because I like to pass smog....

 

UPDATE: 5th time a charm! Finally passed smog. A bolt was missing where the header collector flange meets with the y-pipe flange. So a little leak occurred. I added a bolt. Not sure if this was the problem. The most I drove prior to testing was about 10 miles. This time I drove the car for over 40 miles then pulled right into the smog test station and I got 48 at 25mph on the HCs. 48 is the max so I squeeked by. Sure glad this ordeal is over.

 

until next year..... lol