Failed emissions test

[95Z71]

I have a 95 5.7. It runs perfectly But I had the state emissons test done and it failed. CO% was fine But the HC ppm was 381 at idle (limit is 220) and 386 at 2500 rpm.
Does anyone have a idea where to start? Like I said the truck is running great. I have 30 days to get it straight, Any help would be apprecaited.

Thanks

[95Z71]

I also forgot to mention the truck has had recent plugs, cap, rotor, wires, air filter and temp sensor. Truck has always run well just regular maintanace.
EGR valve maybe?

[idmetro]

Did you make sure the truck was at operating temperature before the test was performed? If the cat isn't hot enough it will not perform properly.

While I haven't had this problem on my truck, I had a smiliar issue on a car I own with high HC at idle.
337 - first test
Changed PCV, cap, rotor, wires, plugs, oil
328 - second test
O2 sensor changed
280 - third test
Changed catalytic converter
23 - fourth test

[95Z71]

Thanks for the responce,
It was at 210 deg for around 1/2 an hour. I am going to do some work to it and make sure I don't have any vacuum leaks or bad wires. The problem is can have it rechecked once for no extra charge. But I may have to start shelling out cash if it fails again.

Any other suggestions are welcome

[1968 Pontiac]

My HC count was right at the limit on it's last smog test with the previous owner. I installed complete new exhaust c/with edelbrock headers and passed with flying colors. My truck doesn't have a smog pump.

One other thing I read when I was researching possible causes of high HC was that high fuel level in your tank may be a cause as too many fuel vapors are being sent to the TBI and not being burnt. I don't know how true that is though.

[idmetro]

Not sure how accessible your cat is but mine had a flange on the downstream side that bolted directly to the exhaust pipe. The gasket was $2.50, when I shined a flashlight into the pipe andlooked inside virtually all the ceramic honeycomb was gone so I was pretty sure that was the problem. Somewhere I read about testing for backpressure in your exhaust system using a vacuum gauge. You could probably google that and it might help you determine if your exhaust is restricted.

[heavyredchevy]

The cat "filters" out the HC's, and is most likely your problem. If your truck still has the stock cat, I would replace it.

[95Z71]

I guess I'll have to look into getting a cat. It is the stock converter. Thanks for all the info.

[silicon212]

Yes, I would check the cat and also the oxygen sensor.

[95Z71]

UPDATE:
The truck finaly passed. I decided to check the distributor again and when I removed the cap it was all green . I replaced the cap rotor and coil. Then ran it to the emmissions station = pass . I don't have the numbers in front of me but they were low. I didn't check the cap at first because it only had about 8000 miles on it and I assumed it was OK. I hope this may help if anybody runs into the same problem.