Air in fuel system.

[mpreiss321]

2011 Int’L prostar cm871 engine getting code spn 94 fmi 18 air in the Fuel system. Not the first time for this code. Have changed the fuel filters recently. Fuel mileage avg is 5.9 mpg with avg load of 25k. Installed 6 rebuilt injectors 50k miles ago. When I turn the key on to hear the fuel pump running, I can hear it bubbling. Engine has 832k miles. Fuel pump and all 4 actuators appear to be originals since they’re all still painted red.

Where do I start?

I did nothing about the code the last time it popped up since it appears to be an intermittent problem.

I have recently changed the turbo with actuator ( work done by international) because the old actuator was frozen and the old turbo spewed oil. Since then it’s lagged in power.