failed emission test, what to do first?

[chromatin]

Well, the oil is only a month and 300 miles old. 50% of this was on the high way @ 80 mph. So I think that wouldn't be an issue.

I went to an antozone store Saturaday afternoon and the ASE certified guy there really really strongly suggested me chaning the oil. He kind of made me feel that he just wanted to sell me some oil and a filter. Come on, a month old Maxlife Synthetic! Now I just feel kind of funny to tell this story.

Yeah, I will give it a nice run this Saturaday and try the free retest. No penalty for another fail anyway. If it does fail, I will think about something else. Thanks guys for the help!

 

[javacontour]

I just wonder if it's not the catalytic converter. I believe that it's the cat that takes care of CO and unburnt HC. So if the O2 sensor checks out, and the cat is the original one that came with the car, you may be looking at the need to replace the cat to pass.

Besides normal tune up items, you may try an oil change right before you go. There could be some fuel dilution in the oil that is getting into the combustion chamber. I believe a good long drive, longer than the 10 miles before the test may be worthwhile. I typically drive 20 minutes AWAY from the test center and then drive back to it, keeping the engine running while in line.

It can't hurt.

 

[RD400]

Good suggestion on a long warmup before checking. It takes awhile to get the cat fully up to temperature before it's working at its best.

I'd also check that the small vacuum line controlling the EGR valve isn't plugged.

 

[Black Thunder]

I've heard that Gas with a small percentage of Ethanol can help lower emissions,

if you aren't using it already it may be worth a try to help somewhat along with the other actions you are taking.

unless of you course you only have the ethanol blend there, here it differs from station to station.

 

[oilyriser]

Another idea is to thermally insulate the exhaust system up to the cat. The higher the temperature of the cat, the better it eats pollution. Even 20 degrees warmer will greatly speed the chemical reactions inside the catalyst.

 

[Billy177]

or you could just fix the problem. the car was designed to pass without insulating the exhaust system or pouring special additives in the gas tank. it probrally just needs a 20 dollar O2 sensor but test it first

 

[Winston]

Rough idle with low CO and High HC means intake leak. Since GM does not know how to design gaskets I would bet it is a problem with your intake gasket.

 

[chromatin]

OK, passed! Here are the numbers:

idle 2500 limits
HC PPM 7 18 220
CO% 0 0.01 1.2
CO2% 14 14.4
RPM 451 2466

I think that guy put the RPM probe in the wrong place. Idle RPM is way too low, only about a half of the right number. He did put it in the right place later and showed the right 910 rpm.

The reason?

intake gasket? NO, and I think only more recent years of V6s have the problem

New air filter? probably not. But I did find my old filter didn't totally seal the housing. The car breathed dusty air for a year! D***! Forgot which brand I bought last time and D*** GM, quite difficult to check the air filter!

g2p? Maybe. Obviously, the engine is burning better.

O2 sensor and Cat? NO.

But I think last time neither o2 sensor nor cat was in their working temperature. Thus The engine ran in default condition and failed!

 

[oilyriser]

Is the slight roughness at idle still there?

 

[chromatin]

quote:

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Originally posted by oilyriser:
Is the slight roughness at idle still there?

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I think so. And I found later on in anther forum that this is not uncommon at all for this engine.

 

[widman]

We have no required emissions testing. Voluntary programs show about 10% of vehicles pass the tests.