no start (with a twist)

[BK75]

Victim:
Mk1 rabbit with an SB code GTD engine.  Bosch certified rebuilt pump 1yr ago.

Condition:
Only when fuel tank is half empty there is a suction loss between tank and pump if it sits for 6-8hrs.  Tank vents properly (also removed cap and condition still occurs).    Just started, maybe 1month ago.  Can't remember any change point at all; it has been running like a top since the engine swap. 

So it does really start (hence the twist)  but it takes ~1 minute of cranking to pull the fuel back up to the pump.  

Corrective actions:
Removed and torqued injector lines.  Replaced fuel filter.  


Please help me diagnose!   Is there a check valve in the fuel tank (I don't find one in the Bentley).   How would fuel level in the tank make a difference?

[CRSMP5]

pull float.. remove screen from bottom of the tank... its got alge build up on it and will do that... a coat hanger with a hook bent into it will catch the top hoop of the screen to remove it..

[ORCoaster]

When you removed the fuel lines and retorqued them did you smooth sand the copper gaskets and then fire them with a torch till they blued?  I did that on mine and do not have the air in lines problem anymore.  Do you have transparent lines on the fuel filter to IP to see if air is getting in there?

[Golf/Jetta]

A check valve should be preventing the fuel from going back regardless if it has a pin hole somewhere. Better find out where it is getting its air from.

If you find out where its leaking in air and it's on the rubber lines where it connects to the hard plastic[/metal] flange, you can use a little fuel or oil around those seems to aid it in the seal. If it's still not sealing the area properly, I like to use gasket sealant (Silicone). Just don't crazy, you don't want it in the fuel line. Just in the edge and around a bit in the line to make a seal. Let it set before you tighten a bit, then wait, then tighten a bit more and so on... That should teach that line to leak.

There is also another check valve on the return line so the fuel doesn't go in the other direction.

That my opinion on how to deal with it but you still need to find where it leaking from. ORCoaster is also on the right track.

How long has it been doing that since the IPs rebuild?

[CRSMP5]

rabbits have NO CHECK VALVES.... the slime on screen in tank does his issue... simple fix/check as thats first to look at..

[ORCoaster]

its got alge build up on it and will do that...  This has to be some sort of creature from the Black Lagoon.  Algae normally needs sunlight to live.  But it could very well be a life form that comes from those sea vents where bacteria live in super heated, arsenic laced water.

Maybe the next time I start seeing air bubbles in my lines I will attack the fuel tank monster living on the screen.  Never did check that one out although I did pull the fuel gauge sender out a time or two tying to get it to show a better range of full to empty.

[fatmobile]

Could even be the little lines between the injectors leaking air into the system.

[CRSMP5]

took less then 3 years to build it up on my 81 coupe..  was a gasser till i did the 1.6na swap in it.. and due to this time i kept refusing it was the issue... finally broke down.. removed the 3 screws and float unit to find a huge clear/yellowish slug looking thing grown into the screen... 

the ones i removed in the late 80s were always black in color..

so no idea what it is.. but it is so simple to check and remove.. would be my 1st look..

why full vs 1/2 tank... grows on it in a way it starves it of fuel.. then creates a suction when shut off when not covered in fuel..

[92EcoDiesel Jetta]

why full vs 1/2 tank... grows on it in a way it starves it of fuel.. then creates a suction when shut off when not covered in fuel..

A full tank provides more pressure. That's why!

[ORCoaster]

So what is it?  Crap coming out of the fuel?  Degraded hoses?  Sounds alien, that's it.  Aliens in our tanks, moving around between states in a manner that they can not be detected.  Very sly.

[mtrans]

Sounds alien, that's it.  Aliens in our tanks, moving around between states in a manner that they can not be detected.  Very sly.

You too?I hanting them from motor to IP to tank to motor to.......
Gremlins on disel/oil.

[R.O.R-2.0]

algae actually does grow in diesel...

[bajacalal]

What's referred to as "algae" by diesel owners is actually a waterborne bacteria that feeds on the diesel.

[R.O.R-2.0]

What's referred to as "algae" by diesel owners is actually a waterborne bacteria that feeds on the diesel.

i never knew that, thanks for that piece of info..

it FEEDS on the diesel?

[bajacalal]

Yes, there are bacteria that will metabolize hydrocarbons.

Though, I think they need water to survive as well, so "algae" in your tank means water is in there as well, or at least it was in the tank where you bought it.