update on long cranking. I have massive air bubbles in fuel line

OK, I was looking at it before starting earlier today and saw no bubbles. Upon closer examination there were no bubbles becase the line is EMPTY. All air! I start getting bubbles coming up from the injection pump inlet right when the car is shut off. Withing 5 mins the fuel line is most empty. Within 30 mins. totally empty. I changed the fuel filter tonight, no help there. Is there a check valve in the injection pump?

also, as the car is idling it looks like a rootbeer float in the fuel line. Full of very fine bubbles the whole time. Will never clear up.

This is your Passat, right?

Sounds like a leak (really?). Most likely in the fuel filter "t" fitting. I'd take it out and make sure the gasket in the filter is there, and not gunged up. Also, take a good look at the t itself, a crack in it could cause this problem. Of course, a bad line, or one that isn't properly tightened would also do it. With a leak, the fuel just goes back towards the tank. It relys on the system to be air tight in order to keep the fuel where you want it.

yes, the 1997. The new filter had a new O ring on it. Would a leak at the T cause fuel to at least seep out of the crack onto the top of the filter at least some? I will go out and check it but I looked things over and saw nothing. Is there a way to spray something on the fittings, etc. to identify a leak?

Generally, from what I've read, you don't see fuel coming out of a crack in the "T" - it doesn't have pressure in the filter, but suction pulling fuel through it so it not forced out. Of course, air is sucked in. I recall some clip holding that "t" on - it's been a while since I did mine - but make sure it's tight and the clip is on correctly. However, this situation was happening prior to the filter change, wasn't it? So that makes the fitting into the filter not likely the problem, but something along the line that wasn't changed - like the T or perhaps a the connection between the line and T. Good luck - this is a task for sufficient light and, in my case, reading glasses or a magnifying glass.

Are you sure you have the correct fuel filter? The ones for the newer models have a different T fitting. The fitting should be snug and almost pop on. The filter should also have o-rings on it, not the tee. The only time I ever encountered air in the fuel line was after a filter change but it soon disappeared after a few 100 kms.

It really sounds like a leak somewhere. How is the condition of the return hoses on the injectors? If they are old they could be cracked and leaking.

The fuel system is airtight so the fuel should never drain back unless there is a leask. Sorry I could not be of more help.

Yes you would. I had a minor leak on one of my injector lines once but I just did not tighten the hardline nut enough.

Any fuel lines up to the inlet of the injector pump is under a partial vacuum while operating. Any fuel lines or components after the injector pump (including the fuel return lines between the injectors, the return line to the filter, and to a much lesser extent the return line to the tank), are pressurized while operating.
The pump has some portions of each. The fuel filter (and thermal valve) also has some lower and some higher than atmospheric sections.
Just to clarify, from which direction are the bubbles coming when the car is shut off? From lower to higher, I know, but from the pump side and moving up or from the filter side and moving up? The search for the source of the air ingress can be limited to the direction from which the bubbles are appearing. Don't be misled by the accretion of all those small bubbles throughout the lines into larger ones. If possible run the engine while heating the thermal valve with a hair dryer. The "rootbeer float" appearance should clear up once the thermal valve has opened, at least on the filter to pump section. Then stop the engine and observe from which side the bubbles appear.

Last night when I watched it I observed what appeared to be the bubbles coming up from the pump right after I shut it off. They were NOT small either but big 1/4 inch sized bubbles. Like I said, within a minute the clear line from the filter to the pump was near empty right after shutting it off. Is there some form of check valve in the pump? I will look at this again close tonight. Thanks for the input.

The fuel can't drop back down to the level of the fuel tank unless there is a way for air to get in. A check valve, if present, wouldn't correct an air leak. If air is leaking into the fuel under partial vacuum conditions, then fuel will leak into the air when pressurized.
Remove the fuel hose to the pump inlet at the filter outlet. Apply pressure to the fuel remaining in the hose and pump. Check for fuel leaking out while pressurized.

Worked on this tonight some. here is where I am. If I bypass the filter supply and return section it is back to normal, no bubbles or air after shut down. Hook it back up I have air. It is a new filter and it acted jsut the same as the old one when the air deal started. That "T" fitting part looks like it has a little relief valve in it. Could that part be bad and causing this?