Help--> Ran out of Gas and the fuel guage still read 1/4 tank?? - The Unofficial BMW M5 Messageboard (m5board.com)

Ocean's M5 · 9th December 2005, 08:51

Driving to Napa with my girlfriend suddenly the car starts to sputter. No "check engine" light and I still have 1/4 tank. Call the 800 number and I'm at 52,000. Call roadside assist and they say I must pay $62.00 for a gallon of gas however they would fix a flat for free...

Apparently tires on our M5's have lifetime roadside assist, but if you need gas you must pay out the *****. Fine i'll pay. I'm in the middle of nowhere.

So the road guy puts a gallon of gas and i get to the gas station and me M5 runs fine.

I call my BMW Dealer and talk with the shop foreman who tells me that there is a Saddle in our tanks that has a fuel pump which sends the gas on one side to the other so that the main fuel pump can take the gas to the engine. "Bring it on in" But no that i'm out of warranty, "bring it on in" doesn't have the same warm and fuzzy Ring it used to.

The raodside guy puts in 1 gallon, and I add 17 more at the gas station to Fill it up. Gas gauge read 1/4 tank and the display said I still had 80 miles to go before empty? Thats the data. Any pokes?

Is it possible to do a DIY for that secondary fuel pump or should i take it to an independent?

thank Sam

E55AMG2 · 9th December 2005, 08:59

Quote:

Originally Posted by Ocean's M5

Driving to Napa with my girlfriend suddenly the car starts to sputter. No "check engine" light and I still have 1/4 tank. Call the 800 number and I'm at 52,000. Call roadside assist and they say I must pay $62.00 for a gallon of gas however they would fix a flat for free...

Apparently tires on our M5's have lifetime roadside assist, but if you need gas you must pay out the *****. Fine i'll pay. I'm in the middle of nowhere.

So the road guy puts a gallon of gas and i get to the gas station and me M5 runs fine.

I call my BMW Dealer and talk with the shop foreman who tells me that there is a Saddle in our tanks that has a fuel pump which sends the gas on one side to the other so that the main fuel pump can take the gas to the engine. "Bring it on in" But no that i'm out of warranty, "bring it on in" doesn't have the same warm and fuzzy Ring it used to.

The raodside guy puts in 1 gallon, and I add 17 more at the gas station to Fill it up. Gas gauge read 1/4 tank and the display said I still had 80 miles to go before empty? Thats the data. Any pokes?

Is it possible to do a DIY for that secondary fuel pump or should i take it to an independent?

thank Sam

sending unit might be dead

willm5ad · 9th December 2005, 09:36

Quote:

Originally Posted by E55AMG2

sending unit might be dead

I had the same problem a while back after having a new petrol pump installed, I thought they had incorrectly installed the level sensor, now it is the other way round so it reads empty when I still have 10 liters in the car, you can see which tank is misreading by doing the dash tests, I think its test number 5 by memory, my right tank only holding 25 liters when it is full whilst the left tank is reading a true 35 liters, so at least I know which one it is for when I can be bothered to have it sorted out.
WillM5AD

Mth_degree · 9th December 2005, 13:04

I don't think there is a secondary pump as such - the fuel flowing in the return line from the engine is used to create a syphon effect and transfer the fuel from the left to the right side of the tank. As suggested above try looking at the left/right readings on the OBC when the tank is less than 1/2 full. If you leave the car at idle on level ground the volume in the left should slowly decrease and the volume in the right increase as the fuel is moved across. If there is only 1/4 in the tank, then eventually the left volume reading should go to pretty much zero, with all the fuel being in the right hand side.

In theory as soon as the fuel level drops below 1/2 if the transfer system isn't working the engine would stall. However if you are driving on a twisty road the fuel will be thrown from one side to the other, so it may run ok until both sides are almost empty.
From your description of how much fuel was added it sounds to me more like a sensor fault. 18 US gallons = 68 litres. I think the tank capacity is supposed to be about 70 so I dont see how it could actually have had 1/4 tank in it. I replaced one of the sensors on my 540 and have heard a few other stories of them going bad, so this could well be it. I measured my new sensor before I installed it, and the resistance varied from about 90-400 ohms from extreme to extreme so if you have a multimeter you could check this when the tank is empty/full.

ilundber · 9th December 2005, 14:00

Two thoughts:

- My wife hade a fuel shortage on the bridge from Denmark to Sweden in our Peugoet. That was very costly since I hade to pay extra to get off the access road when all I wanted to do was to get the car off the bridge landing. However, the problem was that the air inlet was glogged and would not allow air to enter the tank. It was not a problem with the tank lid, they never really found the problem but I could see the tank bottom raise when there was little fuel in it and the engine was running.
Since it, just as with the M5, is made out of plastic, the bottom of the tank was "sucked up" due to the vacuum that was created. That made the fuel sensor indicate 1/4 tank. We never experienced any problems with the engine not running as it should. Have a look and make sure that air can come into the tank.

- How do I access the separate fuel levels on the OBC?

Cheers

willm5ad · 9th December 2005, 14:23

Quote:

Originally Posted by ilundber

Two thoughts:

- My wife hade a fuel shortage on the bridge from Denmark to Sweden in our Peugoet. That was very costly since I hade to pay extra to get off the access road when all I wanted to do was to get the car off the bridge landing. However, the problem was that the air inlet was glogged and would not allow air to enter the tank. It was not a problem with the tank lid, they never really found the problem but I could see the tank bottom raise when there was little fuel in it and the engine was running.
Since it, just as with the M5, is made out of plastic, the bottom of the tank was "sucked up" due to the vacuum that was created. That made the fuel sensor indicate 1/4 tank. We never experienced any problems with the engine not running as it should. Have a look and make sure that air can come into the tank.

- How do I access the separate fuel levels on the OBC?

Cheers

Press the two buttons on the dash cluster for about 15 seconds (mile reset and check control)and the test lights will come on (on the dash not the OBC screen) then press the left button a few times until you see the one you are looking for. If you havent done it already you may have to put the last 5 numbers of your VIN in to unlock the system after pressing the right button. Oh and remember to put your seatbelt on to get rid of the fasten seatbelt warning.
Full instructions on post 11 here
Gadget Freaks II: Fun you never knew you could have [secret menu]
Will

ilundber · 9th December 2005, 14:26

Thank you. Will try tonight

HDClown · 9th December 2005, 14:39

On E46 M3's, it's extremely common for an "out of gas" situation to burn out/put on the fritz the sensor that tells the car how much gas you got (is the sending unit?). I know in mine I went ONCE where I ran out of gas and after that the fuel guage in the cluster was all over the place. I ready many many posts from other owners with the same issue, and it seemed commonplace. If the M5 tank design is similar, this could easily be the issue.

jclyman · 9th December 2005, 17:37

If you knew what had actually failed, you could fix it yourself, if you are adept with tools and mechanical things. But, I'm not sure we know exactly what is failing here. At least, not at this point.

I would recommend a GOOD independent mechanic ... it would not be difficult for a GOOD mechanic to diagnose and fix the problem and certainly it would be less labor than the $tealer would charge.

Stickman · 9th December 2005, 20:51

Hello Sam,
Sorry to hear about your problem. Almost the reverse of what I've seen where my gas gauge acts like a "range gauge" and will suddenly show much less in tank on restart when shifting from HWY to City driving. But in your case, you went to long distance highway driving, which should have caused greater range than showed.

Good luck getting it sorted out.
Cheers,
Alfred