Check Direction Of Flow

Observe direction of flow of bubbles. Bubbles should flow from fuel filter outlet fitting to fuel injection nozzle return system. If bubbles flow in direction described, go to next test for single tank systems. For vehicles with dual tank system, go to the CHECK FUEL FILTER/WATER SEPARATOR FOR BUBBLES  test. If bubbles do not flow in the direction as described, fuel system is restricted. Proceed to FUEL FILTER OUTLET PRESSURE  test under ENGINE PERFORMANCE DIAGNOSTICS.