I've got a 91 Camaro with the 305 TPI setup. In Oregon, every car year 1975 and newer must pass emissions every two years to get new tags. This is the third time I've had to run emissions on this car, and every time I fight it. My hydrocarbons are always too high. The last two times I did emissions on my car, I was only off by about 50 points. All I had to do was go through the testing station about 5-10 times each while driving around at high rpms. This time, no such luck.

The test works like this: you come in and idle. They want you to idle around 900 rpm - my car idles at 500 rpm when warmed up. Then they have you throttle up to 2500 rpm for about 15 seconds. Afterwards, they have you idle again. The test takes values from both of the idles and that gives you your results. Passing values for the test are: hydrocarbon: 220, CO: 1, CO2 + CO = 6. For some reason, only the hydrocarbon value matters to pass.

I went through testing twice today (all I had time for). Test 1 looked like this:

1st idle - Hydrocarbon: 379. CO: 0.6798. CO2 + CO = 11.6798.

2nd idle - Hydrocarbon: 334. CO: 0.6259. CO2 + CO = 11.6259.

I then went and drove around for about 15 minutes in second gear. I made sure to stay above 2500 rpm to really heat the cat up. On my second test, I also throttled up to 2750 rpm between idles to see what would happen. My second idle results went up doing this My second test looked like this:

1st idle - Hydrocarbon: 259. CO: 0.874. CO2 + CO = 11.474.

2nd idle - Hydrocarbon: 350. CO: 0.7575. CO2 + CO = 11.1675.

The second test was better, but still pretty far off on the second idle. In both tests the CO was below 1.0, but the CO2 was above 10. That is definitely way too high since both CO + CO2 is supposed to be 6.

A few months ago I had an issue where the car was hard to start and it hesitated a lot when starting up. It was a fuel issue, so I initially replaced the fuel injectors and the pressure release diagram. This didn't fix it, so then I replaced the fuel pump. The car starts up great now and it runs pretty well, but when it's cold it still hesitates a bit when accelerating from a stop.

Anything I can do to lower the hydrocarbon level? I know I have no vacuum leaks and I have no codes. About 4 year back I put a new egr in it (I was getting a code) and about 2 years ago I put a new O2 sensor in. Last time I did plugs, wires, cap and rotor was when I got the car 4 years ago (about 11k miles since then). I did an oil change about 6 months back (it's been very lightly driven since then). I set the timing to 4 degrees when I got the car per what the sticker on radiator said. The slight hesitation issue makes me wonder if my ignition system isn't functioning correctly which is leaving unburnt fuel. Or maybe the cat is just out on it since it does have 165k miles on it. I'm almost at the point of just taking it to a mechanic and seeing if he can tune it up so I don't have to fight emissions anymore.

 

Hesitating at low rpm under load and from a stop, could be ignition or fuel related.

 

It's not fuel because I get the correct fuel pressure. Maybe I'll check my plugs tomorrow.

 

Not saying it is the issue on your car, but I recently replaced bad valve seals and the that alone dropped HC from 150-350 ish to 28.
HC would climbe while at idle and drop slowly to around 150 with engine at 2000rpm.

 

Well, I threw in a pair of new spark plugs this morning. The old plugs didn't look bad at all. The new plugs did help with the hesitation issue some, but it still does occur (just less frequently).

At this point I think I'm just going to have a mechanic my dad knows diagnose my car. As a college student on a tight budget, I can't afford to keep blindly throwing parts at this car on top of the $140 I'm going to have to pay once I pass emissions for new tags.

 

Back the timing off by about 10 degrees for the emissions test.

 

I'm currently at 6 degrees, so backing it off 10 degrees would put me at -4 degrees. Is negative timing possible? I've never messed with the timing aside from changing it from 4 degrees to the recommended 6 degrees when I got the car.

 

Yes. So, in your case back it off by 12 degrees. No joke. It will run the exhaust hotter and helps the hydrocarbon number significantly.

 

I had the same problem with mine, HC too high 650ppm out of 220 allowed at idle, the other pollutants were very low, cruise speed was never a problem it was way below limits.
All I have for emissions control is the catalytic converter, that's it, and the Demon carburetor is not famous for emissions.
Here are the things I did to get it to pass:
Lower timing from 10 to 4 ported vacuum (ironically the engine loves it)

Wrap the catalytic converter and some of the exhaust pipe in fiberglass wrap to keep it hot ( a must in our cars where the catalytic converter is a mile away from the engine)

Mixed 1 gallon of Denatured Alcohol (Methanol and Ethanol) in 5 gallons of 87 octane gas. ( this stuff burns hot so make sure your cooling system is up to the task)

That was it, the inspector even said "about time" it was the fourth time it was tested in 2 weeks

 

any number of things can cause high HC, worn plugs, bad wires, weak ignition coil, valves, rings, dirty oil & filters, bad gas, weak/dead cat, & the list goes on.

im pretty sure all the numbers matter in your state to pass.
i believe you're miss reading the VIR sheet. normally you see CO2+CO listed as > 6, meaning 6 or higher. if they do use =, it still means the same, CO2+CO = 6 or higher.
CO2 is an indication of how efficient the engine is running. the higher the CO2, the better.
also, CO2 can be used to check how well the cat works.
so with a good working system, CO2+CO will be high.
i have only seen a few vehicles that actually had CO2 below 6, before repairs none of them performed like they should have.

lowering ignition timing can reduce HC, like was said it makes the exhaust burn a bit hotter. but, if you pull too much timing, CO will start to climb.
normally about 2 degrees of timing is about as much as you can pull without causing a sharp rise in CO.
did you set the timing to 4, or 6 degrees?

from what i get here, if i were the one checking this car out for emissions failure, i would be testing for a weak cat.
i have seen some of the emissions fuel additives actually work to get a weak cat to work good enough to pass for a short time.

 

Update: I took the car to a mechanic to see what he could do. He said he was able to get the number down a lot closer (within 40 on both), but I needed a new cat to pass for sure. At this point, I'm just going to try using a few bottles of heet to see if I can get through emissions.

When I took it to him, he messed with the timing. I originally had the timing at 6 degrees because that is what the hood said to have it at. The mechanic moved it up to 8 degrees because that was where he found the lowest HC values at. He then told me to advance the timing another 6-8 degrees after I pass emissions to increase my performance, fuel mileage and completely remove my hesitation issue.

Currently, the hesitation issue is much better. It barely stutters from a stop now. The idle rpm is up to about 550 rpm when warm instead of 500. However, the car idles a little rougher than it used to. Tonight as I was driving around I got a service engine soon light with code 32 - EGR - something I hadn't seen in the 4 years since I replaced the EGR the last time I got the code. The car also died on me tonight when going from park into drive as I drove into my garage.

What should my timing be at? Should I crank it up to 12 or 14 degrees, or leave it at 6 like the hood says too? What if my hesitation issue returns at 6 degrees? What should my idle rpm be when warm? The guys at the emissions testing center and my Grandpa said that if the idle was around 1000rpm, it might pass. The smog testing computer even says to idle at 900rpm. My car as always idled at 500rpm. Is that wrong?

Edit: I looked at a log of data I took about 2 months ago on the car and at 0% throttle my TPS is reading .67 volts. Would adjusting this down to .54 volts help at all?