The Case of the Mystery Missing Fuel.....

[V8 00USH]

Been driving the X5 quite a bit over the Christmas holiday period and 2 days ago was no different.

Fuel was running low so I put £20 worth in (around 16 litres/3.5 gallons) on my way home. Gauge registered the additional fuel as normal.

Got home and parked up, alarm on as usual.

5 minutes later my neighbour came out and told me my alarm was going off as the hazards were flashing. Now I know this wasn't my alarm as there was no siren.I also know this as it's an issue I've been fighting for a while with the hazards randomly coming on and the interior light too. So much so that I've pulled the fuse for the interior light as it was draining the battery. I unlock the car, open the door, lean in and switch the hazards off. Shut the door and re-alarm it and go back inside.

3 hours later I come back outside to go back out, try to unlock the doors with the fob....nothing. Car is completely dead. My cigarette lighter voltage gauge is showing 0.22v. Very strange.

However I put it on charge for the night after fighting with the alarm for a bit until it registers some charge in it and go out in my other car instead.

Next day I go to it - voltage is registering 12.8v once I disconnect the charger. I then try and start it. Engine is turning over fine but won't start. At that point I notice the fuel gauge is registering fully empty - emptier than I've ever seen it before - under the white line. Range showing -- miles.

Where has the 16 litres of fuel mysteriously gone? Gauge fault perhaps although it's never ever done that before. Very strange.

So I left it until today when I had chance to get a jerry can of fuel and throw it in. Did this. Gauge crept up ever so slightly. Car started first turn of the key.

So where did the fuel go?

My initial thought was that somehow the fuel pump had stayed on and drained the battery, ignition switch faulty perhaps - but then if this was the case where would the fuel have gone? I would have thought it would have just returned it back to the tank presuming it wasn't a returnless system. No obvious sign of any leaks.I also thought that perhaps the fuel tank has 2 sides and it's been returned to the other side and the lift pump in the other side hasn't sent it back over. But since running it for a few minutes there was no sign of the gauge moving back up again.

Anyone ever had anything similar on their 4.4/4.6is/4.8is ? I'm completely stumped on this one. It's making me a bit worried about taking it back out until I've got some kind of answer as it could leave me stranded. Will have to carry round a jerry can of fuel just incase!

[crystalworks]

Does your fuel door lock function? If not, perhaps someone siphoned the gas and triggered the alarm?

[V8 00USH]

Yup. Definitely locked as I checked and no sign of tampering. It's parked on the drive and I don't live in that kind of area where something like that would happen anyway. Also it wasn't the alarm that was going off....and lastly I'd been inside less than 5 mins so no-one could have siphoned anything off in that amount of time.

[crystalworks]

Originally Posted by V8 00USH

Yup. Definitely locked as I checked and no sign of tampering. It's parked on the drive and I don't live in that kind of area where something like that would happen anyway. Also it wasn't the alarm that was going off....and lastly I'd been inside less than 5 mins so no-one could have siphoned anything off in that amount of time.

Ah, got it. I'm at a loss then. Perhaps fill the tank and while at idle see if there are any drips under the truck. Maybe a softline (not sure if the e53 has any) finally cracked and leaked a bunch? I had that problem in a couple of e30's with the softlines around the fuel filter.

After that, I'm out of suggestions. Good luck.

EDIT: BTW, this thread title immediately took my back to my childhood and the Hardy Boys/Nancy Drew series' of books.

[jcp240z]

Can you use the display to check the individual levels of the two tanks? If the transfer pump (actually a Venturi pump) stops working then the return gas gets returned to the secondary tank, but doesn't get transferred to main.

[V8 00USH]

Interesting. Just done the test 06 and got the following values....

Screen 1 -
24.7 / 1.8 / 26.5L

Screen 2 -
4.7L Phase 1


Thanks for the hint. Didn't know I could check this. So I believe this tells me where my missing fuel went which is good. - definitely confirmed my original theory.

So 2 questions left...

1. How do I get the fuel across to the other tank so that it computes it correctly? Will it gradually go over by itself over time?

2. What could have made the fuel pump stay on? Ignition switch? Sticky fuel relay?

[Qsilver7]

There aren't really 2 different tanks...it's 1 tank that is bifurcated (has hump that creates 2 sides). The siphon jet sucks the fuel from left side (which is larger than the right side on the e53...unlike the e38/e39 where the 2 sides are basically equal)...to the right side which is where the fuel gets sent on to the engine.

So, Test 6 should show a greater amount of fuel (on a full tank) on the left sde...then it should decrease to "0"...then the right should start to decrease as you continue to consume fuel.

[V8 00USH]

Well I took it out for a 50 mile drive yesterday. By the time I'd done around 25 miles all the fuel had returned to the correct side of the tank and the gauge registered the correct amount of fuel.

Still not sure why the fuel pump decided to stay on....will have to keep my eye on that one I think.

[X53Jay4.8is]

Originally Posted by V8 00USH

Yup. Definitely locked as I checked and no sign of tampering. It's parked on the drive and I don't live in that kind of area where something like that would happen anyway. Also it wasn't the alarm that was going off....and lastly I'd been inside less than 5 mins so no-one could have siphoned anything off in that amount of time.

EWS perhaps for the flashing lights, hazards alarm