How to isolate possible air leak into a VW diesel fuel system?

[SR Heer]

I am noticing what looks like a very slight stream of small air bubbles in the middle of clear hosing going to injection pump.
I thought of spaying hoses and their respective connections with something like WD 40 and watch to see if they cleared up at a particular spot then that might help me isolate possible leak. The I thought of using like a silicon spray because  I know that it works well with rubber tubbing but I did not know what the slight bit of silicon might do getting into the fuel system. Is this a good or bad idea and what have others used to help spot air leaking into fuel system?!?
Thanks
Stephen

[derekp]

I posted similar questions earlier this year, heres some of the things I ended up doing....

- place vacum gauge between pump inlet and fuel filter (hi vacum indicates restrictions like fuel filter)
- Replaced fuel filter - saw vac drop but still had hi (like 4-5 in. hg)
still had lots of air too

- i put a piece of clear fuel line back before my water separator (92 eco diesel has check valve and water separator in r/rear tire area)

- put clear hose in front of check valve.

Noted that bubbles were being introduced at/near check valve.

In my case  I had to replace (actually I removed) the check valve and also replace the "soft" lines that connect to the hard lines.

The fuel filter and check valve caused hi vacum which in turn caused air to get sucked into all the old dried out soft hose connector hoses.

Search the threads about this - but there really arent any great ways to find air leaks.

Good luck...

-
-

[SR Heer]

I have a 91 Eco Diesel - now I know where the water separator is and I eliminated that - where is the check valve in relations ti the water separator?
Thanks
Stephen

[Rabbit on Roids]

in the line from the tank between the separator and the fuel tank.

[derekp]

In my car the check valve was between the water separator and the line that went up to the IP.
I actually bought a new valve (and pair dearly for it)
I opt'ed not to put it in as it was as restritive as the original one.