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 CHECK FUEL FILTER/WATER SEPARATOR FOR BUBBLES test. If bubbles do not flow in direction described, fuel system is restricted. Go to FUEL FILTER OUTLET PRESSURE  test under ENGINE PERFORMANCE DIAGNOSIS.