Lost power and hear air bubbles in fuel tank

[Yeldaw]

My V12 lost power as if it had run out of fuel, had to pull over, it kept running on tick over but would n't rev properly and had no power. The fuel pump was n't ticking as normal, just sounded like a fast dull tutting. When I switched the ignition off we heard lots of air bubbles go back into the fuel tank. The car then started, fuel pump then clicked as normal and ran fine but had same issue the next day. The fuel filter was changed about a month ago and after I pulled over I checked the glass bowl when it was still running at tick over and this was full of fuel. There are no obvious signs of a fuel leak, I can't smell any petrol fumes and the fuel cap pin hole is ok. I am thinking fuel pump on it's way out, a blockage in the system somewhere or a problem with the non return valve, am I on the right track? Anyone else experienced a similar issue and can point me in the right direction.
Thanks
Dave

[dal2.0litrefrogeye]

when you heard bubbling from the tank did you releasethe fuel cap ? and if so did it gasped in air , im thinking fuel tank not breathing and causing a vacuum ??

[Yeldaw]

I only opened the fuel cap after hearing the bubbles and there was no rush of air but if the air had released into the tank already this may not show up. I checked the pin hole in the fuel cap and it seems fine. Is their a separate breather pipe for the fuel tank that I can check and if so where abouts does it run?

[PeterCrespin]

What model is it Dave, UK or American? It probably shouldn't have a breather cap and likely operates with a carbon cannister vapour recovery system - or used to.

Either way, it's a reasonably complex machine and although you seem pretty switched on you really must buy the parts book and workshop manual, because there are bound to be many more questions. You mention a glass bowl but does it have the original style doughnut element or an ersatz one? These are held in place by a spring underneath (where the muck collects INSIDE and the bowl looks clean even when flow is compromised).

[Yeldaw]

Hi Peter, It's a UK model 2+2, I have a manual but it's with the car which is a few miles away from where I live so it isn't really to hand. It has the yellow paper element C28080 with the Spring, I should have mentioned I changed this although the old one seemed clean. I also checked fuel lines and now have checked the non return valve which seemed OK, Where is the carbon vapour recovery system situated, I never knew they had one. I have a spare fuel pump so will try replacing that but can't work out why a fault with the pump would create air bubbles in the tank when I switch the ignition off. Any other ideas greatly received.

[dal2.0litrefrogeye]

hi when you opened the fuel cap , did the car run ok after this ? , also another thought is the coil feeling hot , not normal running hot but to hot to touch , just another train of thought ??

[Yeldaw]

The car seemed to run ok with or without the fuel cap, sometimes it will stall within a couple of mins of starting the engine, other times it can be an hour into the journey. Each time there are air bubbles in the tank when the ignition is switched off which only happens after it has lost power, no issues with the coil which is relatively new.

[42south]

What about sediment in the fuel tank drain. If this gets stirred up it may be creating random blockages.
You could try removing the bolt and see what comes out.

[mgcjag]

Hi...Whats your name.......have you checked out the fuel pumps i know that if one pump fails revs will drop when driving but could you have faults on both....you already mentiond they didnt sound right.......you may be mislead by concentrating on the bubbles

[Yeldaw]

I have changed the fuel pump and it now seems to be running ok, the new SU pump seems to have a double click when it primes the fuel system after turning on the ignition whilst the old pump has always had a single click ever since I bought the car about 4 years ago. As the SU pump is effectively a double pump a double click sounds logical, is a double click normal? Maybe only one side of the old pump was working and this was finally starting to give up the ghost. Fingers crossed this now works, thanks everyone for your help with this.
Dave

[nefematic]

Dave,

I think S3 had the carbon canister venting and thus shouldn't have a vented cap. If I understand the concept the vented cap would comprimise the vacuum effect a bit. Since you were running fine with the vented cap that obviously shouldn't be the cause. Also a PO might have deleted the cc system and fitted the vented cap.

Martin

[nefematic]

What model is it Dave, UK or American? It probably shouldn't have a breather cap and likely operates with a carbon cannister vapour recovery system - or used to.

Peter in regard to Dave's problem, what would be the difference in UK-US build?

Thanks,

Martin

[PeterCrespin]

The US cars had a lot more plumbing and valves of various sorts but I don't carry those spaghetti pictures in my head. If I was trouble shooting I would refer to the manual and parts book.