Just failed emission test, now what do I do?

[walker]

Here are the numbers from my emissions test

loaded read loaded std idle read idle std
HC 115 450 180 450

CO 4.54 3.75 1.76 5.00

So, I passed on all but loaded CO, which I failed by 0.79. As it is right now it has a 1405 edelbrock, with one step leaner metering rods, initial timing at 5*btdc, total timing is about 24*ish, idle is at 750rpm, idle mixtures screws are set to lean best idle, new air filter, changed oil, I do have a pcv system (no more road draft tube). The test is a rolling at 34mph. I am running regular 87 octane fuel and did add a bottle of dry gas(isopropyl alcohol).
So what do I tinker with before I take it back, any suggestions would be greatly appreciated.
Thanks, Walker.

[Martin64]

Just failed emission test, now what do I do?

Know anyone with a Ca. address you can use?

[tomatocity]

you have done everything I would have suggested. What was the last things you changed or modified? How many miles are on your engine?

[walker]

I had just done all of the items on the list. THe engine has less than 10k miles on it.

[pickemup]

run it leaner and or put a cat on. hotter plugs you need to burn more with less fuel

[woodman13]

I ran into a similar problem with a 6 cyl truck, I had done a complete tune up the week before. I changed the oil and filter, drove to the testing station the evening before and parked in the parking lot. The next day I was the first guy in line with my cold engine. By the time I finished the testing my loaded CO was within acceptable tolerance and I was barely up to operation temp. Don't know why, but I know it worked and I was driving my 67 Chevy LB with 6 cyl and 3 sp to work the same day all legal!

[pjmoreland]

I'm not sure I'm remembering this correctly, but I believe high HC means there is too much unburnt (raw) fuel in your exhaust, which would most likely be caused by weak ignition, and high CO means ignition is occurring, but the gas is not burning ideally. Your HC readings seem to be very low, which is good, and I believe indicates that your ignition system has good spark. I'm thinking that your primary jets/rods are too lean, or your ignition timing is not advanced enough.

[kwmech]

Close --- CO is fuel delivery or raw gas, and HC is the engines ability to burn the fuel (or CO) HC is partially burnt fuel. So if you have high CO the engine is working hard to burn it, thus high HCs. Then again if you lean out an engine you can have a lean misfire and have high HCs also.

[pjmoreland]

Here's an interesting article about the combustion of gasoline with oxygen:

http://www.madsci.org/posts/archives...3229.Ch.r.html

Here's part of the article:

The combustion of gasoline is a very complex chemical process for there are over 500 different hydrocarbons in gasoline plus many other elements and additives.

Hydrocarbons ( HCs ) are any molecules that just contain hydrogen and carbon, both of which are fuel molecules that can be burned to form water ( H2O ) or carbon dioxide ( CO2 ). If the combustion is not complete, carbon monoxide ( CO ) may be formed. As CO is burned to produce CO2, it also becomes a fuel.

So based on this article it looks like HC=unburnt gasoline, and CO=result of incomplete combustion.

It seems to me that the most likely way to get high HC is if the ignition system is not working well, and therefore not igniting the fuel consistently. Since your HC is very low, I'd say your ignition system is producing consistent sparks to the spark plugs.

If the high CO is a result of poor combustion, then it seems to me that there are two likely causes:

1) The ignition timing is not correct. If ignition occurs too late in the combustion cycle, then the air/fuel mixture will not have time to burn adequately. Five degrees advanced seems a little low to me. I'm thinking 8 degrees might be better.

2) The air/fuel mixture is not correct. If it is too rich, then there won't be enough oxygen to burn all of the fuel present, which in my mind would also result in high HC which you don't have. If it is too lean, then the flame will have a hard time spreading throughout the entire cylinder. You said you have your jets leaned out a bit.

I would suggest either advancing your timing a bit, or rejet your carburetor to be slightly richer. It would be a good idea only to change one of these things before having your truck tested again, so if it gets worse, you can tell which thing you changed caused the problem. If you change two things at once, there's no way to tell which of the two things caused the problem.

[Jefe]

Turn your timing down to close to 0 degrees if not 0 degrees. That will cure your problem right up.


Douglas.

[Gary]

Wow they make you pass emissions with a truck made before emissions was even thought of? That's kinda harsh. On one hand I'm glad we ain't got inspections here, that is until I get behind some early 80's Dodge mini van that's boiling out more oil smoke than a mosquito sprayer, in downtown city traffic no less.... then I almost wish we had them, until I read a thread like this, then I'm kinda glad again we don't!

[rage'nrat638]

i had the same problem....
switch to a 2 barrel carb......problem solved......

[Lumpy33]

Andy, I am in AZ and also had the exact same problem you speak about. Took me 6 times through the testing station to figure it out.

pjmoreland wrote:

rejet your carburetor to be slightly richer

I kept going leaner because i thought i was getting too much unspent fuel. But making it richer will raise you HC and lower your COs.
PM me and let me know if you pass would ya?

Lumpy33
72 c10 step

[edmonton72]

Make your truck run on propane. It has very low hydro carbons and has over 100 octane.

[Tycoon4u]

When I lived in AZ, I used to pull my 'Cuda in the line at the emissions. Open the hood while I was in line and turn the fuel screws in on the carb in til it barely ran,then it would pass.

[QKENUF4U]

up your idle to a 1000rpm+ as you get in line
richen it up a bit at the carb
and i agree with 8* timing
also if ya can find it, put a bit of race gas in (worked for my bud on his bike that wouldnt pass, #'s came down quite a bit)

from what im seeing your having a LEAN MISFIRE
and
be real careful with that alcohol, if you put too much in it will lean out the motor and burn it up.
and
it prob. aint a bad idea to put a high flow cat on it.
when/if i get my 67-72 thats exactly what im gonna do, true duals w/ high flow cats and flowmasters.

[GloryHound]

Just put some 93 octane (available at the pump) in and a little octane boost. After you pass emissions you can start adding your 87 octane back in incase your engine isn't build to run on High octane. My dad's 63 impala requires lead additive to run right do to the valves. With the small margin by which you failed this should bring you right in. I can't believe they have you testing vehicles as old as our trucks in Arizona. With a population per square mile of land ratio Arizona has you would think it would be an emisions free state.

[walker]

Here is what I have discovered so far. HC failures are due to incomplete combustion, and are generally ignition related (too much advance, bad plugs/wires/cap). CO failures are due to overfueling, and are generally induction related (high float setting, leaky power valve, wrong sized jets, leaking needle and seat, stuck choke.
In other words high HC's are fuel that is going through the engine but not completing the combustion cycle. This would be corrected by resetting the timing, gapping the plugs, correcting any misfires
CO failures occur when too much fuel is going through the engine, but is burning completely. That means you timing and ignition cycle is working good but your air/fuel ratio is just too rich. This could be corrected by resetting float levels, changing to smaller jets, making sure the choke opens all the way, checking needle and seat for leakage.
HC and CO failures occuring at the same time could be a combination of the above listed items, or could also be a vacuum leak causing a lean misfire condition.
This list is by no means all inclusive, as I am working on a carbureted non emissions controlled engine. Fuel injection or vacuum controlled stuff adds a whole new level of difficulty. Also, a lot of this information was pulled from ADOT documents, and was backed up from some internet surfing.
Now, last night I was changing the jets to make it leaner. I just went to Edelbrocks web site and looked up the specs for the #1403 carb that is tuned for fuel economy and is street legal in 50 states. It has the same body as my 1405, but different jets/rods in it. So I installed them in my carb. When I went to start it up, no go. I wouldn't even try to fire, so I went back and checked my work, checked for fuel, checked for spark, none. I figured I must have knocked a wire off the dizzy, but no. THe wires were all on but no power. As it turns out the wire that feeds the power to my HEI, behind the fuse box is burned, insulation melted, and the terminal is rusty. Apparently it has been gettting wet in the rains and started having a bad connection, started arcing and had burned away the coonnector. What a rotten time for that to have reared its head. I guess it is a blessing in disguise. Now you all know what I am doing today!

[pjmoreland]

Did you happen to find any information about what happens to the HC and CO readings if the mixture is too lean? I'm wondering if lean misfires cause high HC readings, like an ignition-caused misfire would cause high HC readings. I find this all very interesting.

I had a truck that had high HC readings because three exhaust valves were leaking. I'm guessing the air/fuel mixture was leaking past the exhaust valves before ignition.

[walker]

Got the new jets and metering rods installed and passed with flying colors, the new 3's are loaded HC 68, Idle HC 146, Loaded CO 1.83, Idle CO .72. So thats that!
Thanks for all the help and suggestions.