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My 1994 Chevy Silverado failed the smog check on all emissions, CO , HC and NO. What could be the problem?

Can you give me some hints on what to do to get my 94 Chevy Silvardo to pass the smog test below are the results. 15 mph HC(PPM) Max = 113 Mine = 147 CO(%) Max= 0.57 Mine = 0.64 NO(PPM) Max= 980 Mine = 1530 25 mph HC(PPM) Max = 90 Mine = 136 CO(%) Max= 1.00 Mine = 0.61 NO(PPM) Max= 840 Mine = 1497
Answer:

Though call... All emissions (CO, HC, and NO) are high. The CO problem could be a fuel mixture problem; your Chevy Silverado may be running rich. The HC problem is more then likely due to the high CO. High CO (partially burned fuel) will almost always cause high HC (raw fuel). And the NO problem, is probably a problem all in itself; due to a bad EGR valve or EGR component. We recommend having a certified smog check repair station perform a complete diagnosis on your 1994 Chevy Silverado to avoid you replacing emissions components unnecessarily. posted by SmogTips Support

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