Diagnosis And Testing - Air In Fuel System

DIAGNOSIS AND TESTING - AIR IN FUEL SYSTEM

Air will enter the fuel system whenever fuel supply lines, separator filters, injection pump, high-pressure lines or injectors are removed or disconnected. Air trapped in the fuel system can result in hard starting, a rough running engine, engine misfire, low power, excessive smoke and fuel knock.

Inspect the fuel system from the fuel tank to the injectors for loose connections, Refer to Service Precautions. Leaking fuel is an indicator of loose connections or defective seals. Air can also enter the fuel system between the fuel tank and the fuel pump. Inspect the fuel tank module and fuel lines for damage that might allow air into the system.

With a diagnostic scan tool connected to the vehicle, view the fuel pressure set point and actual fuel pressure. Start the engine and observe the fuel pressure set point and the actual fuel pressure. If the actual fuel pressure fluctuates above and below the fuel pressure set point in a regular cycle, inspect the fuel system for air leaks.

If the actual fuel pressure gradually drops below the fuel pressure set point then spikes well above the fuel pressure set point, replace the fuel pressure solenoid, also called the pressure regulator valve and recheck.