Basically, a nywhere that's convenient on the feed side of the fuel system, between the fuel pump and the fuel rail. It is ideal to install the flex fuel sensor on the feed to give the ecu the most accurate e85 content reading.
GM E85 Flex Fuel Sensor Connector Pigtail Plastic Fuel Composition Ethanol E85-2
GM E85 Flex Fuel Sensor Connector Pigtail Plastic Body Fuel Composition Ethanol
E85 Flex Fuel Sensor Bypass Kit - works w GM 13577429 13577379 FULL FLOW ETHANOL
Aeromotive 15141 Billet Inline E85 Flex Fuel Sensor Bypass Adapter Mount -10 ORB
E85 Flex Fuel Sensor Split-Flow Adapter -10AN ORB Flow Rate 5/8'' US,
Flex Fuel Sensor Bypass Splitter Flexfuel -8AN In/out LS CTSV E85 (No Sensor)
