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Originally Posted by truckin 79
I have failed CO emissions test twice and have adjusted idle mixture screws the second time around. I replaced all filters, air, crankcase and canister. It did help but still high HC and CO are way high to pass. I am starting to think either cat or egr might be the problem. The truck does run well for the most part. I can press down on gas pedal pretty hard and truck does not do much. I did stomp on gas pedal and could hear secondaries open up but still no wow affect. The truck is a steady performer though, if I just give it a little gas it will accelerate fine. On a side note what is the temp on cat? I have a temp gun and it was about 350 degress when pointed at cat
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If you have high hydrocarbons and CO your cat could be on its way out. Is it the original pancake style cat or a newer high flow one? The EGR lowers combustion temperatures which helps NOX emissions. You should measure the temperature of your cat before and after I THINK the temperature should be higher after the cat. Another thing I would check is the condition of your spark plugs if they are sooty or worn out you could have weak spark which will increase hydrocarbons and CO. Adjust the carb to maximum vacuum as well.
EDIT: is the truck the one in your signature? 79 Big 10? I don't think those came with a catalytic converter???