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#563997 - 05/15/05 11:49 PM What causes high hc emissions?
Ironduke4 Offline

Registered: 05/07/04
Posts: 179
Loc: Chicagoland illinois
I have a 1995 cavalier with the 2.2L pushrod engine and it failed the emission test.
The hc emissions are a bit high .80 is the standard and mine is at 1.20 the co emissions are ok.
I have never had a problem getting a cavalier to pass i wonder what could be causing the high hc?
The car has new spark plugs and wires,air filter,cat converter,O2 sensor and pvc valve so it should pass with no problem.
Any ideas?

#563998 - 05/16/05 12:07 AM Re: What causes high hc emissions?
HondaMan Offline

Registered: 04/06/05
Posts: 671
Loc: Texas
The cause is incomplete combustion.

It could be from weak spark, timing, air/fuel mixture... etc.

How was the tune-up you mentioned performed? What type of parts used? Any hot-rod type parts?

Sometimes non OE style wires can cause all sorts of problems with ignition system for example.

#563999 - 05/16/05 12:10 AM Re: What causes high hc emissions?
wavinwayne Offline

Registered: 01/06/05
Posts: 7522
Loc: North Alabama
Does the car have a conventional distributor-type ignition system? If so, replace the distributor cap & rotor button.

The only other thing that comes to my mind is a bad Mass Air Flow sensor.

Just out of curiosity, what grade of gasoline were you running when you failed the emissions test?

#564000 - 05/16/05 12:41 AM Re: What causes high hc emissions?
1sttruck Offline

Registered: 03/20/04
Posts: 4378
Loc: Camas, WA
If you have an older engine that's prone to burning oil you could try using a heavier oil.

#564001 - 05/16/05 03:38 AM Re: What causes high hc emissions?
JTK Offline

Registered: 08/14/03
Posts: 8182
Loc: Buffalo, NY
A misfire, or like HondaMan says, incomplete combustion can cause it, but given the age and the fact you dont list any performance or economy issues, I'd say your catalytic converter is tired. How many miles are on the car? A fresh cat will eat up the HC's.

#564002 - 05/16/05 05:05 AM Re: What causes high hc emissions?
JHZR2 Offline

Registered: 12/14/02
Posts: 36861
Loc: New Jersey
yeah seems odd. were you using premium gas or something like that?

I guess at 10 years old, the cat might be getting old... a 95 isnt a new car anymore (though it seems to me like 1995 was yesterday)

WHy did you change your o2 sensor? If it went bad, maybe before you replaced it a bad mixture caused the cat to burn out?

Have you ever had a check engine light?

Did you go for an emissions test with the engine cold? Did you run it to full hot (at least 15 miles so oil and cat are fully up to temp) before going? A catalytic converter that fails to fully "light off" might not be processing HC efficiently.


#564003 - 05/16/05 11:32 AM Re: What causes high hc emissions?
Ironduke4 Offline

Registered: 05/07/04
Posts: 179
Loc: Chicagoland illinois
The car has a new cat converter i just put it on in march along with a brand new exhaust system it's all walker from the cat to the muffler. The only thing on the car that is not stock is an obx stainless steel header and a dynomax super turbo muffler.
I know that the muffler would not have anything to do with the high hc but what about the header?
I drove the car for 20 minuits prior to the emission test so it was all warmed up.
The spark plugs are oem AC delco and the wire set is an oem style set from autozone i was running regular gas when i took the test.
It has never has a check engine light come on and the car runs fantastic not a problem at all with the way it runs.
The only thing that i can think of that might be causing it to fail is the obx header what do you guys think?
If i put the old manifold and head pipe back on it might pass although i dont see how a header could cause it to fail [I dont know]
I would really hate to have to take the header off i really love the burbly sound it gives to the exhaust system it has a nice rumble when it is idleing [Big Grin] .

#564004 - 05/17/05 01:04 AM Re: What causes high hc emissions?
mechtech Offline

Registered: 08/11/04
Posts: 2387
Loc: Chicago area
High HC is misfiring. Hich CO is rich.
With cat conv cars, the cat is always suspect.

#564005 - 05/26/05 10:56 PM Re: What causes high hc emissions?
Sam3 Offline

Registered: 04/11/05
Posts: 73
Loc: Chattanooga
Here's a link to a 14 page .PDF file from toyota
re: 4 and 5 gas emission analysis.

#564006 - 05/26/05 11:20 PM Re: What causes high hc emissions?
drm7 Offline

Registered: 05/19/03
Posts: 541
Loc: Virginia
A friend of mine always told me to blast a tank of fuel injector cleaner then run the car hot before the test and you can get a car that fails to pass. Might be worth a shot of Seafoam. Cheaper than new parts.

#564007 - 05/27/05 12:26 AM Re: What causes high hc emissions?
Sam3 Offline

Registered: 04/11/05
Posts: 73
Loc: Chattanooga
Just this year they started smog checking here.
I didn't expect to pass' but I did. They only checked for HC, CO, and CO2
but not NOx?

My car has a squish hight of only 0.018"
so my main concern is combustion chamber deposits!
else I'll get a piston slapping noise.

I get the best results useing "fuel products" that claim to clean up Conbustion Chambers (PEA)ratherthan just "cleans injectors"

Don't know what Seafoam is. I like lotsa PEA in my gas.

#564008 - 05/28/05 01:42 AM Re: What causes high hc emissions?
1977c10phxdriver Offline

Registered: 05/04/04
Posts: 294
Loc: Phoenix Arizona
High HC readings can be caused by a lot of different or combined problems. Over advanced ignition timing, intake leak causing a lean cylinder, weak plug or a failing cat. HC is just unburned fuel.

I too agree that the cat is suspect at this point. Cats are designed to eat up small amounts of emissions over a long period of time, not huge amounts of emissions. Your's is very close to passing so i'd double check the base timing and verify that it is vacuum leak free. Replacing the cat may be your next option providing the entire engine and ignition and fuel system are operating properly.

#564009 - 05/31/05 08:59 AM Re: What causes high hc emissions?
xchemie Offline

Registered: 05/30/05
Posts: 1
Loc: Chicago
I had the problem of slightly high HC on my Honda. After much digging for info, I checked the thermostat: the installed t-stat was a lower temp rating than stock; replaced with recommended rating and passed the second time. I bought this car used, so the previous owner must have changed it...

#564010 - 06/04/05 05:27 AM Re: What causes high hc emissions?
Ironduke4 Offline

Registered: 05/07/04
Posts: 179
Loc: Chicagoland illinois
Thanks for the suggestions guys but i have one question.
Today i found a hose that goes to the evaporative emission control charcoal canister that was disconnected i don't know what it does but would that have anything to do with high HC emisions?