Ford Mustang 1989-1993 Repair Guide

Fuel Tank Vapor Orifice And Rollover Valve Assembly


See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Cross-section view of the vapor orific and rollover valve assembly

Fuel vapor in the fuel tank is vented to the carbon canister through the vapor valve assembly. The valve is mounted in a rubber grommet at a central location in the upper surface of the fuel tank. A vapor space between the fuel level and the tank upper surface is combined with a small orifice and float shut-off valve in the vapor valve assembly to prevent liquid fuel from passing to the carbon canister. The vapor space also allows for thermal expansion of the fuel.


  1. Disconnect the negative battery cable.
  3. Relieve the fuel system pressure as follows:
    1. Remove the fuel filler cap.
    3. Attach fuel pressure gauge T80L9974B or equivalent, to the fuel diagnostic valve on the fuel supply manifold.
    5. Relieve the fuel pressure into a suitable container.
    7. Remove the fuel pressure gauge.

  5. Drain the fuel from the fuel tank as completely as possible by siphoning or pumping the fuel out through the fuel filler pipe.

There are reservoirs inside the fuel tank to maintain fuel near the fuel pickup during cornering and under low fuel operating conditions. These reservoirs could block siphon tubes or hoses from reaching the bottom of the fuel tank. A little perseverance combined with different hose orientations will overcome this situation.

  1. Raise and safely support the vehicle.
  3. Disconnect the fuel hoses and tubes.
  5. On vehicles equipped with a metal retainer that fastens the filler pipe to the fuel tank, remove the screw attaching the retainer to the fuel tank flange.
  7. Position a suitable jack to support the fuel tank and remove the bolts from the fuel tank straps.
  9. Lower the tank just enough to gain access to the vapor orifice. If necessary, unplug the electrical connectors to the fuel pump and sending unit.
  11. Remove the vapor orifice valve.
  13. Installation is the reverse of the removal procedure.