wjsmarine

Hi All,

I just joined the forum being a newbie to Audi having bought my daughter a 2004 A6 1.9TDi with Multitronic trans 2 days ago. I'm in Perth, West Australia.

There is some white smoke when first started so assume this is valve seals for its 262,000km. The previous owner didn't speak very good English so couldn't tell me much about its history or even if the timing belt has been changed - so I'll be undertaking some maintenance soon. The car pulls well and has only been driven around town, no country driving yet, and shows 6.9l/100km as expected.

A major problem was experienced today when the car ran out of fuel with 3/4 showing on the gauge. I added 20 litres, it started and the gauge went to full. Suspecting a faulty fuel gauge or sender I headed to a fuel station.

It only took 8 more litres confirming the sender and gauge are probably okay - but why did it run dry and how do I prevent it again?

If anyone has experience like this or can offer some things to check, it would be appreciated.

Thanks in advance,
Bill

georgeb944

Things to check:

1) Fuel gauge sticking at 3/4 mark
2) Fuel sender sticking at 3/4 mark
3) If it's a quattro, the fuel tank is weird in that it has more than one chamber and the fuel is pumped from one chamber to another by a jet pump, driven by return fuel from the engine (at least on the gas engines.) That jet pump may not be working correctly.

You can test the fuel gauge and sender by removing the fuel pump/sender from the tank and operating the float to see if one or the other is malfunctioning.

Well, the good news: Now that you know what full is, you can keep an eye on the elapsed mileage since the last time that you filled up and refill it when you get to a certain point (it might be 3/4 tank or it might be 200 miles, for example.)

Of course, here in the USA, daughters tend to be dingbats, and don't pay attention to the fuel gauge or the mileage... I don't know about Aussie daughters.

SloopJohnB@mac.com

Dunno about Aussie engines.

jcman

Yep most all of the VW/Audi diesels before cats and low sulfur fuel smoked white at a cold start up and then black when loaded, good ole memories of the once owned 81 VW Dasher 1.7 manual with a whopping 80hp but 40 mpg was unheard of then and quite amazing outside of the 0 to 60 performance that I won't even mention.

wjsmarine

Hi Folks,

Thanks for the feedback and comments. I'm still investigating but not much time available this time of year so will get to it when I can and report the findings (carrying a spare gallon of diesel in the trunk/boot as a backup).

Actually the vehicle is a "grey import" from the UK according to an official sticker on the inside rear wheel arch, but I don't think Aussie vehicles would be any different from normal Euro production in any case.

Cheers,
Bill

wjsmarine

Hi All,

My daughter experienced another breakdown since topping up the tank to overflowing - this time traveling only 86 suburban km's before the car died. The emergency 1 gallon container did the trick and got her home again for me to investigate.

Well a full day of removing the tank swirl pot/pump/sender unit and testing resulted in no further light on the problem. The tank was very full of course so this was a messy exercise.

The pump tests perfect in a bucket of diesel - both full discharge from the main outlet and a high pressure squirt from the second outlet at the bottom aimed at the non-return flap inside the pot. Nothing faulty seen, no split hoses or loose connections, all appears correct.

The fuel sender unit also tested faultless in resistance throughout the range so it's safe to assume the fuel gauge is reading correctly and the small variation I did see are indicative of tank level.

I took the opportunity to wire an indicator LED directly at the connector on top of the tank swirl pot with the LED cabled to the dash under the carpets. If the LED never goes out when it stops again I'll know it isn't a pump power supply problem.

I also disconnected the fuel filter outlet and installed a T fitting to monitor the fuel pressure with an under-hood gauge - it measure 0.6 bar running, but I don't know if this is normal or what this should be...

I don't want to buy another tank pump if I can avoid the expense. Assuming the LED does not extinguish at any time and the car stops... I have a spare EFI (petrol) external pump I could wire in and re-plumb hose connections to see if it's the tank pump or not. What is the consensus?

So given the above information does anyone have any ideas I can pursue?

Thanks for your help,
Bill

wjsmarine

Hi All,
I dislike open threads so have come back to close the issue and can report the problem appears to be solved. Having tried everything else, I removed the small flap non-return valve in the bottom of the swirl pot/canister housing the pump in the tank.

Since doing so the car hasn't missed a beat and has traveled about 1,000kms returning 5.4 l/100km - outstanding.

I believe this valve keeps the canister full of fuel and comes most into effect when the main tank is nearing empty - the trick here is don't let it get that close to empty before filling up again. BTW the flap looks perfect and is free to move but will remain out.

Regards,
Bill

clancy

Makes sense to keep the fuel near the pump when it it running low.
Thanks for providing the solution.

I had a 2.8 gas A6 that was also acting as if it was out of fuel when below 3/4 tank. In my case the reason was the fuel pickup had broken and floated up toward the top of the tank. So it sucked air instead of fuel. There was a plastic fitting that held the pickup at the bottom to the tank that broke and allowed the pickup to float toward the top of the tank.