We get a decent amount of questions regarding fueling and possible fueling related issues with different aspects of getting fuel, in the correct pressure, to and from the fuel tank and throttle body. In this article we will attempt to cover as much as possible related to throttle body fuel injection and how to provide proper fuel to the system. Please keep in mind we are only discussing fueling for throttle body fuel injection. Other systems such as Multi port fuel injection are sometimes routed differently and are not discussed in this article.
An external fuel pump may have been included with your TBI system. This pump delivers a constant pressure to the throttle body where it is then regulated down to 10 – 13 psi and returned to the fuel tank. This pump should be mounted to the frame or body of your vehicle in an area that will be protected from the elements as best as possible. The fuel pump should be mounted below the fuel tank fuel level for the pump to work properly. If necessary put a cover over it to keep the environment away form the pump. A fuel filter is to be installed in the fuel line PRIOR to the fuel pump. Premature failure of the pump can be the result of improper fuel filter installation. Some aftermarket high density fuel filters can cause a large drop in fuel pressure under load and are not recommended for use with your system. If you are using one of these types of filters insure that you have proper fuel pressure during all modes of operation. Recent fuel pump installations have kept the vehicle’s mechanical fuel pump intact and used it as scavenger pump for the electric fuel pump. With this type of installation the electric fuel pump can be mounted in any location that you would choose, as a constant fuel flow is available for the electric pump. Ensure that the fuel filter is still installed between the mechanical and the electric pump if you choose this type of fuel pump installation. A 12 Ga. pink wire labeled “Fuel Pump”, with sufficient length has been included with the wiring harness for the pump power feed. This wire comes from the fuel pump relay, which is mounted on the inside of the vehicle. Very important for proper operation of the fuel pump is the mounting and the ground. A ground wire is to be attached to a good clean body ground or run back to a battery ground. An improper ground will result in insufficient fuel flow and or premature pump failure. Mount the fuel pump in the rubber brackets supplied or similar, to keep the pump noise from radiating into the vehicle. You can use the mounting screws supplied with the pump, or supply your own to ensure proper mounting. You may want to “prime” the fuel feed line with gasoline to aid in the priming of the pump for proper operation.
FUEL LINES A TBI fuel injection system requires two fuel lines for proper operation, a feed line and a return line. Some vehicles are built with two lines for this purpose, even with carburetors. If you are starting from scratch, you will need to install both of these lines from the fuel tank to the Throttle body. Usually a 5/16” or 3/8” line is used for the feed, and a 5/16” or ¼” line for the return. If you do not have a place to return the fuel to the tank within the fuel-sending unit, parts are available to return the fuel into the filler neck tube. Use only fuel line and fittings approved for fuel injection.