Gurgling in the fuel tank

Fylnn · January 17, 2013, 11:11:24 PM

I have an 83 GTV6 with the fuel tank in the boot. It has had for a while a gurgling sound in the fuel tank like air bubbling into the return line in the bottom of the tank. I never paid much attention to it but recently it has also decided to not run cleanly, won't pull and just fluff's and breaks down. On a dyno today it is fluffing because it is running lean. Which has got me wondering is there somehow air in the system. It had a new fuel regulator earlier this year but i wonder now if there is not some problem with fuel regulator diaphragm or similar that is allowing air in. But then I would think if it lets air in it should let fuel to leak out.

Anyone come across 'gurgling' fuel tanks before?

Doug Gould · January 18, 2013, 11:30:13 AM

Its the rust troll hiding in the fuel tank.

Doug Gould · January 18, 2013, 11:31:43 AM

Seriously, I think I'd check the vapour lines & vapour tank behind the rear seats at the top.

Fylnn · January 18, 2013, 12:30:05 PM

I should add the tank has been recently removed and resealed and yes before that it was full of rust. But now is clean. the vapour lines are at the top of the tank. The bubbling is apparently the return line from the injectors at the bottom of the tank. The real issue I am trying to diagnose is that the car started off with an intermittent miss under load. It has got worse and worse to the point now where it has leaned right off (according to the dyno man) and won't pull at all. It just breaks down on multiple cylinders and fluffs. i don't want to drive it anymore in case I melt a piston or something.

So I am pondering is there some condition like a fuel injector seal, or dodgy pressure regulator that seems to be allowing in air, but not allowing fuel out? Which in itself seems a really strange thing for a totally pressurised system.

Al Campbell · January 18, 2013, 01:27:41 PM

Winns make a Mylanta for Rust Trolls.

Sorry 'bout that but that cracked me up Doug.

Can't see how air would get in to a pressurised system, if there was a leak fuel should be going the other way. So... Running crap, gurgling, might be stuff all pressure at the injectors.

Have you checked the pressure that you have at the injectors?

The manual says you should get 32 to 38 psi at the injectors with the vacuum hose to the pressure regulator disconnected. Or if like me you don't have a fuel safe pressure gauge, the manual also says you should also get 1.5 to 2 litres a minute delivery at zero pressure. That'd be into an open container ( a standard plastic bucket is around 9 litres) from the pipe coming from the fuel pump.

*** Be bloody careful you don't have any spark sources if trying that. Disconnect the coil, don't use the starter, maybe a jumper across the right terminals of the double relay, help from a mate &c... Pressure pump hosing a tank full of fuel onto a fire would be bad.

AL.

Al Campbell · January 18, 2013, 01:30:24 PM

Oh, has the weather been hot? Twice in my life I've heard petrol boiling in a fuel tank on a hot day. Car still ran fine 'though - '76 Mazda. Just a thought.

AL.

festy · January 18, 2013, 03:44:49 PM

Does removing the fuel cap make a difference?
Or if it's air getting into the lines, it could be from the low pressure side of the pump? If it was a problem on the high pressure side, you'd expect to see fuel coming out rather than air getting in but if the pump pickup was a bit clogged, it could be sucking air from somewhere caused by not being able to draw fuel in properly creating a vacuum?

But I agree it could also be fuel boiling, worth checking that out too.

Fylnn · January 18, 2013, 05:09:09 PM

thanks for the comments. The gurgling in the tank might just be fuel flowing. The primary problem is for some reason the engine is running lean. One theory is it is not getting a clean fuel supply. The presure regulator is new, but I will pull it off and check it anyway. But other way could be too much air. i got the injectors cleaned but can't remember (which probably meant i did not) replace the seals. Might start looking in those areas for problem.

Going right back to the start, the car was running fine until one really hot day when it was on rough dirt roads (it is a rally car after all) then it started missing, fluffing and farting until it died. Never been much good since. I just haven't had time until now to track it down. It also has a new fuel pump.

Jekyll and Hyde · January 18, 2013, 06:49:45 PM

Quote from: Fylnn on January 18, 2013, 05:09:09 PM
Going right back to the start, the car was running fine until one really hot day when it was on rough dirt roads (it is a rally car after all) then it started missing, fluffing and farting until it died.

Maybe a crushed fuel line (hard pipe), restricting flow? Didn't bottom it out or throw up any big rocks or sticks?

Fylnn · January 19, 2013, 10:16:04 AM

Fuel lines have been moved inside the car. As was commented i find it hard to believe that air could get sucked into a pressurised system without fuel coming out. Only on the suction side of the pump and similar logic would apply i would think.

Maybe the gurgling is a red herring just something that i can hear in a stipped out car. The real dimena is why is it leaning out, better look for air leaks there.

AikenDrum105 · January 19, 2013, 10:41:45 AM

I had an issue similar to this and it was the intake of the high pressure pump sucking air in with the fuel (and it was Festy who pointed it out that time too...) - rather than air getting in anywhere else - as you say, pressurised system makes that pretty hard.

Thought I had the HP pump intake hose on tight - but the threaded fitting was letting a little air in.

Easy enough to run the return line into the bottom of a large container and watch for bubbles perhaps ?

Fylnn · January 19, 2013, 09:49:44 PM

Yes excellent suggestion. Will pull the return line off the regulator and run a line into a bottle or something and look for bubbles.

When you say the inlet fitting was loose you mean the banjo fitting on the bottom of the tank or something else?

Fylnn · January 20, 2013, 02:30:09 PM

OK so I pulled the return line off the regulator and there is a steady stream of bubbles running into a clear container. So went back to the source. Put a line direct onto the fuel pump outlet and the stream is clear, no bubbles. Then moved up to the line where it goes into the injector manifold and it is clear as well. So from that I surmise that it is getting into the system between the injector manifold inlet and the outlet of the regulator. Any ideas?

Al Campbell · January 21, 2013, 08:32:21 AM

The vacuum tube from the pressure regulator to the intake plenum is the only source of air leak left from what you describe.

If you haven't replaced the vacuum tube between the regulator and the intake plenum with new stuff, this would be a good time to do so. Use clamps at both end of a type that look like they exert pressure all the way round the circumference. Disconnect the plenum end, plug it with something like a phillips head screw drive shaft, clamp as well and try the free-flow test again.

If the replacement pressure regulator is a used one too, maybe it's full of oily goop and blocked open or something. I don't know how they work, but maybe there is a path between the vacuum side & the fuel side that is stuck open. If it is used, try giving it a damned good clean with something like degreaser and/or carby cleaner before doing the flow test again.

Good luck,

AL.

Fylnn · January 21, 2013, 05:03:37 PM

All the hoses are new on the vacuum, but i can still check for leaks. The plenum joiners need replacing so onto that and see how good the clamps on there are. The replacement regulator was brand new. The injectors are the originals that were ultrasonically cleaned.

When I say 'bubbles' it is like a constant stream of tiny bubbles a bit like foaming. I could put the old regulator back on and see if there is a change after plugging up the hoses as suggested.