Cadillac

Hi. I'm failing smog in California. Shocking, I know.

Anyway, this is the first time I've failed the sniffer and the largest change in the last year is the addition of a full 3 inch cat back exhaust with high flow cat. With my NOx levels so high, either my EGR is wasted (seems to be functioning fine) or my cat is not getting hot enough to be effective. I already dialed the timing back to 0*,

Anyway, I have a theory that if I can increase the back pressure in the system (at least for the test) I can get more 'work' out of the cat.

Questions:

1.) Is this a valid theory?

... and if so:

2.) How can I increase the back pressure?

I was thinking I could stuff one of the dual pipes with foil or something and that would do it (single in, double out, Flowmaster 80).

Any ideas?

slow_90firebird

Well, high-flow cats are known to produce alot more emissions than a stock cat (equally good working order of course). So, its kind of a gamble wheather they will be able to pass. Alot depends on how the motor is running.

I dont know if increasing backpressure will help emissions. Its worth a try, though. What I have heard of, is stuffing the pipe with a wet sponge. I think it might blow out, so maybe try stuffing each pipe with a piece of sponge? Idk, I would try it in the driveway first tho.

Another trick people use to help with emissions is, run your gas tank as close to empty as you feel comfortable. Go to the gas station. Put a whole gallon of "Denatured Alcohol" from home depot in the gas tank. Add another 3 or so gallons of high octane gasoline. This will give you about a 1:4 ratio.

Depenfing on what you failed on, you should probably let the car to idle in the parking lot before they bring it in. This will get the temp up nice and hot.

Cadillac

Deantured alcohol? There's a new one. Is that really safe? Same combustion properties as regular gas but a cleaner burn?

Concerning the cat, I've been told to bomb down the highway in third gear at highway speeds to get the cat warmed up. I've also been told that the "high flow" is the problem too. I'm kinda in denial about that one though.

Thanks Adam!

TraviZ

iTrader: (2)

I will be using some of that stuff in my methanol kit, Mike. It's safe as far as using it in your engine is concerned from my researches.

Dyno Don

iTrader: (7)

Mike:
Have you forgotten that I told you how to fix this problem?

Forget that myth about high flow cats, all cats today are the same, as far as flow goes.(monolythic cores)

Where your problem lies, is in the fact that with a better flowing system you will need a little more vacuum to the EGR to make it work right.

Remember, I told you to drill the hole where the vacuum line goes on about .020 larger. That will help to open the EGR better, lowering the NOX.

Cadillac

I remember Don! I thought that was to kill the SES light in highway mode. Now that I think about it they must be related, right? Where do I get a drill bit that small? I'll figure it out...

I hope you are doing well down there. Thanks for the reply!

slow_90firebird

Well, I know this isnt on a third gen, but was on my last car. It was a '95 chevy Monte Carlo FWD 3.1L v6.

I had the stock 10 year old cat on one year. Passed emissions with flying colors - just a fraction of the alloted stuff.

Next year, had a brand new Catco High-Flow welded in. Failed with twice the allowed values. And, 1 year later, the engine was in alot of better running condition with all the maintenence I had done.

To resolve the issue, I got the cheapest $55 magnaflow cat I could find online. Welded it in series right behind the Catco. Now, 2 cats passed. But just barely passing, by 1ppm on the HC's.

Cadillac

Closure for the story. I installed a new EGR drilled out with a .02 drill bit to provide more vacuum and then had the shop run the car on the dyno for a good 10-15 minutes to warm up the cat and it passed with flying colors. HC's, NOx, and all the others ended up well below the allowable limits here in Cali.

Again, help from TGO provided a great bit of piece of mind.

slow_90firebird

Thats good news. I have no idea how the EGR valve even works, but where did you find a .020 drill bit??

All the bits I have here are like 1/16, 3/32, 1/8 ect.