1982 Chevy Silverado v8 5.1L failed HC with ignition timing off.

Yes, your 1982 Chevy Silverado may very well pass the smog check after the ignition timing is corrected. Ignition timing has a tremendous affect on hydrocarbon emissions. In this particular case your Chevy Silverado's timing should be at 8 degrees BTDC (Before Top Dead Center), it is instead at 3 Degrees BTDC. The fact that the spark plugs are firing later rather then sooner will not allow fuel/gasoline (HC) enough timing to burn fully before exiting the tailpipe. Setting the ignition timing correct to 8 degrees before top dead center should lower HC. We say should lower hydrocarbons only because several other components will affect HC emissions. Assuming all other emission components are functioning properly and your Chevy's engine is sound, ie. Good compression, correct carburetor adjustments... HC should be much less on the next smog test.

posted by SmogTips Support

2nd QUESTION: Thank you for your answer i should have been more specific the hydrocarbons meausured 348 at 15 mph ave is 67 max is 138 and at 25 mph meas was 271 ave 40 and max 83 could it be somthing else like the cat converter ? 2nd ANSWER: It could be the CAT as well, but this will not be known until the ignition timing problem is corrected and your Chevy retested.

posted by SmogTips Support