Question: Fuel Guage Problems

[ElementalFiend]

This is a new problem which I have never experienced before in any car..

Scenario: I top-off the gas tank in my car, everything is fine and the car has been running fine. That is until I drive half a mile, turn onto the interstate on ramp and accelerate. Then all of the sudden the fuel guage instantly drops to empty! I crap my pants, pull over the car, check for leaks or any undercarriage damage, and find nothing. I get in, start the car back up, and the guage is back at full again.

Everything is fine for the rest of that day, and most of the next until I go and top-off my fuel again. This time I don't even make it out of the gas station before the needle drops to below E. I stop, recheck everything, and it looks visually fine. Start the car back up.. but it is still on E. Turn it off, wait several minutes, turn it on, and its still on E. So now I have a car that is on E no matter how much gas is in it.

What is causing this?? How do I fix it? As fun as it may be to drive around guesstimating how much gas is left in the tank.. I'd rather not get stranded on one of my city to city trips I take so often.

[1996 328ti]

Sending unit?
I think it is accessible under the rear seat. Not sure though.

Your temp gauge is not also going down, is it?
I had that happen a few weeks ago. Nlown fuse.

[ClubSport]

This dropping fuel gage thing is a pretty common problem with our cars. The exact same thing happened to me. I restarted the car and it hasn't happened for a couple months now. I assume it's only a matter of time before my sending unit fails.

[ElementalFiend]

Hmm, well its happening every single time I fill up the tank completely now. (happened again tonight). SO, I think it may have something to do with a full tank of gas, because it seems to be fine when I start the car up and it isn't full.

Whats this about a sending unit? Is this a part that is known to go bad?

[ElementalFiend]

Oh, and no the temp gauge doesn't go down too, its only the fuel. I've checked the fuses (while trying to deal with my brake light problem) and all of them seem to be in good condition. So i'm pretty clueless as to the cause or whats going on..

[ClubSport]

Yes, the sending unit is known to go bad. It's basically a thing that sits in the gas tank, reads the level of fuel, and sends it to the computer. Luckily it's easy to get to from the interior of the car, if you remove the back seats. There are two removeable black panels that go down into the gas tank.

[ElementalFiend]

Hmm okay, I plan on removing the rear seats soon anyways. So that works. Any idea on the cost of one of these things?

[J!m]

The sender / fuel pump is bad.

I had both of mine replaced under warranty. They produced a better replacement part, so I suggest getting the factory part for DIY'ers...

It is under the rear seat- run down to 1/2 tank or less to avoid a mess in the car.

Also try to work quickly- the gas smell will be hard to get out of the seats and carpeting if the tank is open for more than a few minutes..

[ElementalFiend]

Thanks. Any specifics on how to replace the sender pump? I'd prefer to do it myself if at all possible.

[Turbo-ti]

Just remove the tank cover and you will se the sending unit and pump assembly..Pull up on it and you will have to kinda twist it up and out or you will break the sending arm off and it will stay floatin in your tank..Then just insert the new one in the same manor. Make sure you get a small hose clamp and do away with the stupid crimp clamp that comes with the new unit..Then just put the tank cover back on and hook up the plug and test it out...

[ZeroG]

Originally Posted by Turbo-ti

Just remove the tank cover and you will se the sending unit and pump assembly..Pull up on it and you will have to kinda twist it up and out or you will break the sending arm off and it will stay floatin in your tank..Then just insert the new one in the same manor. Make sure you get a small hose clamp and do away with the stupid crimp clamp that comes with the new unit..Then just put the tank cover back on and hook up the plug and test it out...

I have had this issue as well. It is the sender that is with the fuel pump under the rear seat. Replacing this sender will surely fix the issue.

-Chad

[bmwracefan]

Before you go replacing stuff, disconnect the battery and put the cables together for 15 min. This will reset the computer. Nine times out of ten its just a computer glitch. I've had this happen before on more than one model of BMW.