Cant pass smog my hc levels are to high - 1987 Oldsmobile Cutlass Supreme

The easiest way to reduce HC at idle is to retard the timing a few degrees. You might have to increase the base idle and you will notice power loss, but the settings can be returned once vehicle passes inspection.

as long as you have no check engine light on change oil, air filter. pep boys sells a product called guaranteed to pass add to fuel make sure car is hot when you go back for emission test cold car has high hc levels it also helps to post the hc level you tested at and the limit on your receipt hope this helps

Other than testing the EGR valve, not many options. You really need a 4 gas analyzer to know what is coming out of the tailpipe. Otherwise you won't know if repairs have helped the problem.
When you say EGR numbers I'm not sure what you mean. Most of the time the test is for CO and HC gases, along with oxygen and Nox also in some areas. The EGR valve allows some exhaust gas to be recycled thru the engine and reburned. CO or HC could be high if the EGR system is not working.

Hydrocarbons (HCs) are unburned fuel. You may need to replace sparkplugs and wires, if this has been done or doesn't fix the problem you catalytic converter may be worn out.

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About the only thing you can do is take it to a qualified DEQ specialist and have them take a look at it. It might be something as simple as a hose, or not.

Are you burning oil? Does this car still have a catalytic converter? Have you changed spark plugs or air filter recently. There are many causes for a high hydrocarbon reading: burning oil due to rings or valve stem seals; catalytic converter malfunctioning or missing; vehicle in need of a tuneup or air filter replacement. Poor combustion results in high hydrocarbon levels. Good luck with it.

fist i would like you to post the year make and model of the truck along with the HC ppms and NOX ppm it would be very helpful but high hc and nox can be attributed to a faulty EGR system nox is produced when the combustion chamber temperature gets too high so a small amount of exhaust is cycled back into the air stream to help cool them there are other causes but without looking at the levels its much harder to say

High HC means moisture in the system. Try driving it longer then take it to the smog shop. Otherwise it could be hard like a head gasket or easy such as a PCV not functioning. Any ways you should always drive it about 20 miles before smog check, longer when the weather is cold.

We had to have the calatic converter replaced. We did this after doing an oil change, air filter change, and new spark plugs and still hadn't passed smog. After changing the calatic converter it passed smog with scores of 25.

Do an oil change with 20W50 oil (or one grade higher) to prevent blow by during the test.

You current oil has HC from blow by though the rings.

Do a fresh oil change will lower the HC.

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Change spark plugs,wires,cap and rotor if they are over 24,000 miles
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Make the smog check appointment for the EARLY MORNING. Colder air will help the fuel burn better.

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Clean or change the air filter and pcv valve.

Clean Mass Air Flow sensor with CRC Mass Air flow cleaner or electronic part cleaner.

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Do a quick wipe down on the wires and cap to take the moisture off.

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Check spark plug wire contacts for corrosion.

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Fill the tank to around 3/4.......just in case your fuel pump is weak.

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Ran the truck for 20+ minutes on highway before the test.

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Do not carry excessive cargo on the truck bed.


These are the little things I would do to get the HC and CO down.


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