Tiny air bubbles in fuel lines
 

https://www.dieseltruckresource.com/forums/2nd-gen-dodge-ram-no-drivetrain-90/getting-air-fuel-return-line-295450/page3/

I have posted a link here successfully I hope. It is a 3 page trial and error of a member chasing down the source of air after the vp. I am getting air after the lift pump. Not getting high pressure out of the lines. I used bluechip website instructions for the 3 tests for vp failure. All indicated vp needs replaced, unless....
Air these champaign bubbles in Joel's return line and my supply line what needs addressed first?
Is it normal to have air in a bled fuel system?
While letting the lift pump prime the fuel system for the 100th time I heard a significant change of sound like air cavitation or fuel loading. It happened twice on different days compared to the many times the pump noise was uniform.
I have been able to release a small batch of tiny bubbles from the water separator both times.
Is it normal for these filters to produce or release air bubbles or like an aerator on a faucet.

I've been following these threads, I may be on the same leaky barge.

If you have air on the supply side? You have a line compromised between the lift pump and the pickup screen in the tank, allowing air to enter your feed line.

If it's after the VP, there is a chance that you have a bad injector seal, cup, or tip allowing small amounts of combustion gases into the return fuel side. This is basically the only way that air on the return side would be under enough pressure to enter the fuel system. Unless of course you are getting air before the VP, and simply not seeing it until the return side.

If you have a loss of prime, it can have two major sources. One is a leak in the fuel feed line, allowing fuel to flow back to tank when the system is not running. Another is a bad fuel return line, allowing the fuel to siphon away from the injectors
Again while not running. I have seen this one more on older engines.

Carefully examine your lines, check valves, etc for any signs of damage, dirt, or bad seals. You will locate the problem.

Thank you. I will follow this trail. Feel good about it. Thinking of disconnecting the line in to the lift pump and sucking fuel from a gas can to start.
Really appreciate your time.

Regarding the air in the supply line:

For what its worth, I had what I thought was an air leak in a supply (suck side) fuel line. I was fighting a fuel prime/fuel pickup issue, so I wired in a Holley Blue fuel pump very near the tank pickup with clear fuel lines from pump up to the filter to test. What I had laying around. All kinds of bubbles in the clear lines while running. Thought i had it figured. It did run and no noticeable issues, just bubbles. And still lost prime.

I've had two separate instances where the bled fuel system loses prime. The hard line Tee fitting/return fuel line at the back of the head was slightly loose at the compression fitting nuts. Half a turn and it keeps prime.

I've heard that Holley Blue pumps work, but I would not recommend them for diesel. It was the Holley Blue pump cavitation - I think - making the bubbles. The pump vanes are at a different angle for gasoline vs. diesel if you compare the stock Cummins to a Holley. Anyway, I switched out that Blue pump near the tank with a new stock Cummins LP retaining the clear lines in place and the bubbles went away. Put the Cummins LP in the stock position by the engine and its worked ever since.

Great reply, thanks.
Today I put a clear line to the tank from lift pump and watched the big airlocks and bubbles do various things from prime and have many tiny bubbles, and it also bled back with vigor a few times, not a consistent happening so I was glad for the clear.
I used a vacume pump to suck the fuel through from the line out of the filter to vp and sure enough my tank to lift pump extra long clear tube completely primed and did not bleed back. This tool is essential for so many bleeding possibilies that would be nightmarish without a vacume pump.
Anyway with that line primed and holding nice I continued to get tiny bubbles in mass but not from the tank to LP line it was clear of any bubbles.
This means eliminate the filter housing and suck on the line from lift pump with nothing but the stock steel line.
I sucked on it and tiny bubbles continued so it must be the banjo bolt line on the suck in side of the lift pump that has a perforation.
Tomorrow buy a new banjo line for that side of the pump.
I still feel vp replacement is imminent being damaged by all the no fuel cranking etc.
Maybe lucky but it was smoking too much anyway so even if it still works it's no longer primo.

I installed the new vp. Truck runs better than it ever did, no smoke unless it's from the tires when I step on it. All the bubbles meant nothing.
I am looking for a cheap option to watch the LP pressure, $90 for a light seems too steep. Any ideas.?

May be aeration from the return line dumping back too close to the pick up line...just a thought.