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You can try that but if your check engine light is not on it won't help. Try to get the engine hot before you take it through emissions testing. If it still doesn't pass you will have to change the catylitic convertor. I had ths same problem in a 93 Silverado with a 305. You can also try to do a tune up on the vehicle if that hasn't been done in a while. The timing will be the most important part of it because that will determine where the engine fires and how well all the fuel gets burned.

  • high HC typically is due to unburnt fuel- cat. converter and timing. The '93 vortec motor with electronic ignition automatically times itself and with EFI adjusts the fuel delivery based largly on the O2 sensor input. If no engine light is on then the O2 sensor is probably okay. The EGR valve allows exhaust gas to re-enter the cylinder to reduce temperatures so as to prevent the formation of NO (nitrogens of oxygen) a seperatly tested molecule by at least CA Smog stations.
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โˆ™ 2015-07-16 19:24:33
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Q: If a 1993 Silverado did not pass state inspection due to high hydrocarbons and carbon monoxide should the EGR valve and oxygen sensors be replaced?
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