TBI Fuel Flow

For TBI illustration purposes, this fuel flow diagram is shown using the older style vapor separating tank (VST) system.

The low pressure pump brings fuel from the tank, through the filter and fills the reservoir. The reservoir fills from the bottom up and supplies fuel to the high pressure pump. The high pressure pump pulls fuel from near the bottom of the reservoir and supplies the fuel rail and injectors.

If the fuel demand is less than the volume of fuel supplied by the pump, line pressure will increase until the regulator opens and allows fuel to exit the regulator and return to the reservoir.

Fuel entering the reservoir is cooled by incoming water. A smallvolume of water moves through a passage at the base of the reservoir.

Inside the reservoir is a float and needle mechanism that connects to a manifold vacuum line. The vapor rises to the top of the reservoir, vacuum pulls the vapor into the intake. A pulse limiter in the vacuum line prevents a backfire from igniting the fuel vapor.

As the liquid fuel level rises, the float and needle mechanism closes and prevents fuel from entering the vacuum line.

On high vacuum (18+inches Hg) small blocks, the VST needle wouldstick if not clipped correctly to the float tang.