91 Silv keeps failing Texas Emissions

[teufel]

I have a 91 Silverado, extended cab, 5.7L V8 with Automatic Trans. I keep failing the hydrocarbon emissions test. I easily pass all other parts of the test. I replaced plugs (gapped at .035), wires, air filter, muffler, pcv and O2 sensor. Still fails. Basically no change in values. I am going to replace the thermostat just in case it is running too cool. I checked the suction coming out of the throttle body to make sure it wasn't clogged. What the heck do I do now?

 

Thanks!

 

Robert

[Rolandd]

if your tank is low put in about 5% by volume 99% isopropol alchohol. The alchohol is an oxygenate, meaning that it will carry more oxygen molocules into the combustion chamber. This solution will work if you are close to passing. Otherwise I would look at your cat converter.

[RyanZ71]

Definitly look at the Cat Converter and Charcole (sp) Canister.

[lrymal]

Definitly look at the Cat Converter and Charcole (sp) Canister.

 

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My vote as well, especially the canister and also any of the hoses and lines going to it.

[teufel]

Thanks for the suggestions guys. It was the CAT. Cost me 300.00 to have a new magnaflow cat put on. But it dropped my hydrocarbons from 650 down to 52 ppm at the 25mph test.

 

 

Robert