My heads/cam car just failed emmisions...barely so I need to know where I should start with tuning. The cam is the gm846 grind 222/230 .544/.563, 112lsa. It failed the HC with a 1.2. The standard is .90. The other 2 tests passed with flying colors. Would a lean base tune help out HC? Thanks for your replies.

 

Thats what ive heard. Lean it out and try using some of that stuff from autozone which is supposably guaranteed to pass emissions in your gas.

 

Thanks for the reply. I looked at a bottle of that "guarantee pass" and saw that it's supposed to clean the deposits from the combustion chamber. You're supposed to run a bottle through a full tank of gas until almost empty then refill the gas tank and take the test. I don't think it will actually lower emmissions by itself.

 

Gasline antifreeze and denatured alcohol are said to work also.

 

where would I find denatured alcohol?

 

Paint supply stores, like Sherwin Williams. Home Depot and Lowes might have it also, although I never found it there.

 

How much alcohol would you suggest adding to a tank of gas? How o2 sensor friendly will this be?

 

I've seen people lean the low end out soo bad just to make emmisions. i've also seen a pretty extreme case where a nitrous bottle filled with air is injected into the exhaust to help the readings.

 

I went back through with a lean program but still failed. In fact, the numbers were significantly worse than before.

 

How did you lean it out? What tables did you change? Are you running a closed loop tune (ie still using O2's)? The computer uses the O2's and tries to get the a/f to 14.7. There isn't anything you can really do about that. You could run an open loop tune and lean the hell out of it. Then, just put the tune you have back in it. I'll wait to see what your doing before I explain how to do this.

 

put the stock cam back in...once you change the cam your screwed if you want to pass emissions.

 

Untrue. He ALMOST passed. It can pass. If all else fails, go to the junk yard, pick up another catalytic converter, weld it inline and try again. I've seen some pretty wild cars pass using this method.

 

That cam is fine for passing, I've passed with bigger cams. Try the guaranteed to pass first, don't try to figure out how it works, just use it and find out. It contains some alcohol like the other things I recommended. You aren't that far from the standard for passing so that might do it.

By leaning out the tune, you can sometimes cause misfires which will raise your HC's. I never had any luck leaning the motor out. I am assuming your cat converter is good and somewhat new? I've had 1 year old aftermarket replacement cats not pass, and once a brand new one was put in, it passed. After that, I only put the cat in for the test once a year in another y-pipe.

I will have to find my old tuning notes because I am in a state that doesn't have a test anymore.

Off the top of my head though:

1. retard your initial timing back to 0* degrees, it will raise the combustion temps for a more complete burn, power will suck driving to the test, but once you get back home, just switch tunes.

2. raise the fan cut-on temp to 210-215 degrees, the hotter you can stand, the better, if you ever notice once you fail the first time, the emission tester will ask you to raise and hold the throttle to 2000 rpms, this is to get more heat into the motor and cat converter, then they take another reading. Make sure the car is good and hot, if there isn't a line, pull off to the side and sit and wait at idle until the motor at least gets above 205*, then pull in for the test.

Hopefully that will get you by the test. If not, you could drill a hole before the cat and using different size holes, introduce air right before the cat to get it to burn hotter, I've heard of people doing that with an extra O2 bung before the cat but I never tried it.

Other tricks I've heard of but never tried:

-using (engine builder) rocker arms, usually 1.2-1.3 ratio, which comp cams says each .1 ratio equals roughly 2 degrees in cam timing
-injecting air directly into the pipe right before the cat converter, which is similar to the O2 bung trick above

The hardest thing is to find someone with a 5 gas analyzer that will actually let you tune your own car on it in their shop. When I lived in TN, no one would let me just come in and tune my car on their gas analyzer, I guess they didn't want to deal with it. I even started bidding on gas analyzers on ebay, sometimes you will find old shop equipment for cheap, but the 5 gas analyzers aren't cheap. I needed the 5 gas to pass in TN, since TN test for 4 different gases. Some of the analyzers on ebay are older and only test for 1 or 2 gases.

Since you aren't that far from passing, try the guaranteed to pass, and if that doesn't work, retard the timing and raise the fan temps and use more guaranteed to pass.

My old cam was like 2500 on the hc's and passing was like 200, so I needed all the help I could get, which was why I was going to tune with the 5 gas analyzer, use the lower ratio rocker arms, use the denatured alcohol and all the tuning learned from the gas analyzer. My old cam was 242-254 .555-.585 110 lsa in a 383. I've passed with the LPE 219, and a 230-236 .600-.604 114 lsa in the past.

 

Found a good post from Thirdgen.org:

http://www.thirdgen.org/techboard/di...%252A+AND+lean

 

The tuner set the computer to open loop and leaned it out a bit.