Searched...even though I am a wheeler now.

Kinda stuck on this one - my project samurai came in fairly well on the smog test, but failed idle HC at 241PPM, twice the max. The funny thing is CO% and O2 are close:

2500 RPM CO% .77, O2% .5
Idle CO% .39 O2% .5

At 2500 RPM HC is 106, allowable is 180.

If it was a misfire or something causing incomplete ignition, I would expect that CO% and O2% would be out of whack. As I understand it, if HC is high due to incomplete ignition, O2 will also be high as there is a lot of unburned oxygen.

Could a bad cat keep CO% down but not HC? Hate to start spending $$$ blind.

Thanks for listening

Brian


Oh Yeah - one more thing - while searching, I saw some posts about high NO - but that is not measured on my CA smog test. That is nitrous oxide, right? Where is that an issue if not CA???

I can't remember all the smog trouble resolution stuff at the moment but I seem to remember EGR valve and manifold leaks causing major problems

My egr valve was working but this flapper valve that was on the charcoal canister that was tied into the egr system had a tear in it I repaired the flapper valve and every thing worked fine

There are two common causes for high HC numbers: misfire or bad compression. Your mixture may be so lean at idle that it doesn't ignite. You may also have an erratic spark at idle, but this is usually more of a problem at high RPM. It is not unusual that the O2 numbers aren't too high if you have a catalyst.

Could also be blowin' oil. How's your oil consumption?

Originally posted by yurtle
2500 RPM CO% .77, O2% .5
Idle CO% .39 O2% .5

At 2500 RPM HC is 106, allowable is 180.

Oh Yeah - one more thing - while searching, I saw some posts about high NO - but that is not measured on my CA smog test. That is nitrous oxide, right? Where is that an issue if not CA???

First, what was your CO2. Carbon Dioxcide will tell you everything about how well your engine burns. If you think that your engine is running good, then your CO2 should be above 13.5%. If it is, and your cat is old....replace it, and forget about it. A brand new cat will allow you to pass the test... no problem.
However, it will not cure the problem if one exsists.

Depending on what year your Sami is (or maybe they all are) it is Carburated, try to lean it out, just a little.. Your Co reading of .77%, and your low o2 shows that you are not running too lean.

BTW, NO is an abbreviation for NOX, which stands for Oxides of Nitrogen, which is the fifth gas measured from a tailpipe. It is measured in CA, but currently only in enhanced smog areas like Sac, and LA, but it will be coming to all areas shortly.

Hope I helped.

Brian--

Damn I love this board. Thanks for the info. PinHead might be on the money - compression is low, but it still runs quite well. It has some blow-by, and I am otherwise sure it is time for some engine work but I want to get the smog and reg done first if at all possible. I want to test some suspension mods before taking the motor down.

1uglyranger, CO2 is 13.8 at 2415 RPMS and 14.1 at 984 RPMS. The idle was a bit high when tested. This would indicates that the stoichiometric ratio is good, I think.

Sounds like cat time. Thanks for your replies.

Brian

Originally posted by yurtle
- compression is low, but it still runs quite well. It has some blow-by, and I am otherwise sure it is time for some engine work but I want to get the smog and reg done first if at all possible.
Brian

Since you are only failing the HC part and your compression is low, the cheap way to pass would be to put a couple cans of "viscosity improver" like STP, motor medic etc. in the oil and retesting. The catalyst isn't as effective at reducing HC.

Samurai is a notorious oil burners. Thicken up your oil. Since you live in CA (warm climate), you may want to consider using a 'straight' 30 or 40 WT (SAE 30 or SAE 40) . The synthetic and mulit visc stuff will seep right by the 3pc oil ring Suzuki used.

I'm not a SMOG expert, but I'd guess oil would be a good source for HC emissions....

Man, so far you you have gotton some terrible advise. High HC at idle is usually caused by a lean condition AT IDLE. This causes a lean misfire and incomplete combustion at idle. the most common causes are
A: vacuum leak. If it idles smothely, it is probably not that.
B:Lean idle screw adjustment. Most probable from what you describe.

try this; set everything by the book with the proper tools. Timing, idle speed ect. Look down in the carb while the engine is running, be sure no fuel is dripping from the venturi. If it is, the idle speed screw may be set too far in, back it off untill the dripping stops. Now, Using a tachometer, turn the idle mixture screw in or out to obtain the maximum rpm. Now turn it back in 1/2 turn. If you can't perform this setup the way I described, you may need to rebuild the carb.
Replace your pcv valve, change the oil a get it retested.

Excessive blowby generally causes high CO, especially at higher rpm.
NOx is oxides of nirogen. the test for it here in AZ

Originally posted by zags
Man, so far you you have gotton some terrible advise. High HC at idle is usually caused by a lean condition AT IDLE. This causes a lean misfire and incomplete combustion at idle. the most common causes are
A: vacuum leak. If it idles smothely, it is probably not that.
B:Lean idle screw adjustment. Most probable from what you describe.
Excessive blowby generally causes high CO, especially at higher rpm.
NOx is oxides of nirogen. the test for it here in AZ

WOW, I can tell your not a smog tech... Because I would fire you!

If you check his C0, and his C02, you can tell there is almost nothing wrong with he mixture, and .77% C0 at idle shows that he is possitivly not too lean!
The point of posting here was to get facts, not your opinion!

Yurtle, go buy a cat, and I garuntee your tailpipe runs spic-n span.

BTW, blow-by does not read anything on a four gas as long as the oil is clean(ie: new). If the oil is old, it probaly has traces of gas in it from the low compression you mentioned, this will also cause high HC, but not C0. Change your oil (I wouldn't worry about 40w, just whatever you usually use), and weld in a cat, you'll be fine.

Brian--

1Uglyranger, I think you misread his original post. The numbers for CO and O2 he gave were at cruise, where it it passed HC. He never gave the idle numbers, he did, however state the the idle was high. On carburated vehicles, I can tell you from experience that someone probably jacked the idle speed to try and cover up a vacuum leak or lean condition.

Sincerely, Larry.
ASE Master Technition, with L1 certification
Ford Master Technition, engine performance specialist
AZ State certified Emmission Technition
19 years experience

ok im just a student at NADC but i have been through our emission class's. it sounds like you are running a little lean and you should probably check your ignition system and make sure it is up to snuff.

Fatter the carb (is it a carb) like maybe 1/4 turn, and change you oil, you will pass, 250HC is nothing, 250 can easily be hiding in your oil, just change you oil, get the truck NICE AND HOT, and you will pass