Yes the cp will check. They have strips that they dip into your tank. Some now have a tester that they just hold to the exhaust that tells. The fine is a few thousand dollars. I have friends that have been caught here in Ne. It is not worth it.well doesn't all of this have the sulfur we need in our vehicles? I know its highly illegal, but do yu think a cp when he pulls you over is gunna check your fuel?