Fuel system test question #2

1994 Merc 4.3LX

OK, so I got all the parts to hook the test rig up. Put it between the fuel/water separator and the pump. Started her up, and the tube did not fill with fuel; an air bubble remained where connected tot he separator. With this being the case, could not tell if the separator was allowing any air into the system. At that point I was getting a but frustrated, so I didn't do the pinch test to check vacuum.

So my question is this... should the fuel system upstream (before) the pump be fully filled, or is it OK for there to be the bubble? Did I do something wrong?

Re: Fuel system test question #2

At idle you will probably keep that air bubble. The test needs to be done under load and at speed.

You could also have an air leak in the pickup or lines up to the pump. Without finishing the test, the air bubble does't really mean much.

Re: Fuel system test question #2

Thanks Don.

This may get one of those.... "that's a really stupid idea" responses, and I'm okay with that, but as I'm doing this alone, to simplify things for me, I've gotta ask it..... If I tie up very securely ( 2 or 3 docklines on both bow and stern lines, and put an extra fender between the hull and the dock), can I do the test under load, but not at speed? As a point of interest, right now I'm not getting above 2500 rpm without bogging, so if I tie up, have 4 lines total (2 bow 2 stern) and turn the wheel slightly to port (I dock bow-to with the dock on my starboard side) will I have too much thrust to be able to do this safely? I could always come in stern-to and ties up both stern cleats as well, but then if something goes wrong I'm launching into the boats across the way, rather than just driving into the dock.....

You know now that I've typed it out is does sound pretty dumb, I guess what I'm looking for is "naw, it's not too dumb, as long as you do it carefully"....

Thanks,
Don

Re: Fuel system test question #2

ummm I think they call it "recipe for disaster" if something were to fail.

Re: Fuel system test question #2

You are familiar with the Darwin theory ???

Re: Fuel system test question #2

Tie a rope from the tow cleat to the dock! And take it tubing!

Re: Fuel system test question #2

Yeah, I figured that I was asking for these types of responses...

Re: Fuel system test question #2

Welp... took all your advice and did NOT do it at the dock. Took her out, brought her up to where she stumbles, then backed off.... air buble in line remains.... as such, no vaccuum readings could be made.

NEXT?