Flex fuel sensors measure ethanol content. They can be used in the FPR return line. But for improved accuracy and faster response times, the sensor should be plumbed upstream of the fuel injectors in the feed line. In this case, expect to see up to a ~10psi pressure drop if multiple pumps are used with a high-powered engine.
Compatible with GM Flex fuel sensor 13577379 and 13577394 found in the Haltech HT-011000, 13577429 found in AEM 30-2200 / 30-2201, ECU Master WHP, MaxxECU 1282, Fuel Tech 5005100353 / 5011100354, and Cobb Tuning kits.