Fuel Gauge not functioning after filling to full

[donutholer]

Recently purchased 1999 bmw z3 2.5l

second time filling the gas, after starting the car the fuel gauge was still marking on empty. Drove a bit and it climbed and now its right above the 1/4 marker.
Tried replacing the fuses per some posts but no luck.

I purchased some chevron high mileage fuel cleaner to poor into the tank when I'm guessing the tank is close to empty. Right now no idea what its at lol.

I saw there is a pretty bad issue with the fuel sensor in the tank, but seems like a really expensive fix, and also that little piece is a bit hard to find. Any other fixes I should try before replacing that sensor?

 

[Delk]

Just a guess but I would bet its the sendor thats worn out. Its made of a set of resisotrs and two brushes that ride up and down on it from the the fuel float.

If you want to confirm the gauge and everything are ok you can pull the plug off the tank and put a jumper on the wires. This will make the gauge go from zero to max since you are changing from open cuircuit to closed.

You remove the cover behind the seat thats held in with four screws. The plug then unlocks and comes off. There are four wires in the plug but six spaces. Two wires are the power and ground for the fuel pump. The other two are the ground and signal for the fuel gauge. The gauge wires are brown with yellow strip and brown with black strip.

If the gague goes up and down then the sender needs to be replaced and its easiest to get an entire carrier that goes in the tank.

 

[donutholer]

Just a guess but I would bet its the sendor thats worn out. Its made of a set of resisotrs and two brushes that ride up and down on it from the the fuel float.

If you want to confirm the gauge and everything are ok you can pull the plug off the tank and put a jumper on the wires. This will make the gauge go from zero to max since you are changing from open cuircuit to closed.

You remove the cover behind the seat thats held in with four screws. The plug then unlocks and comes off. There are four wires in the plug but six spaces. Two wires are the power and ground for the fuel pump. The other two are the ground and signal for the fuel gauge. The gauge wires are brown with yellow strip and brown with black strip.

If the gague goes up and down then the sender needs to be replaced and its easiest to get an entire carrier that goes in the tank.

great info! does the tank need to be empty in order to put the jumper on the wires? And by jumper, what exactly do you mean? a bit of an electrical noob

 

[Nodzed]

You can do a gauge test using the dash buttons. If that's OK it's the sender, no need for jump cables to check the gauge. You buy a new pump and sender for the Z3, not long got one.

 

[Delk]

great info! does the tank need to be empty in order to put the jumper on the wires? And by jumper, what exactly do you mean? a bit of an electrical noob

To test the gauge you don't open the tank so it doesn't matter. Jumping the wires is just touching them together with another wire. You are literally creating the circuit by connecting the wirings and removing the connection. The gauge will not act fast so you will have to keep them connected for a bit.

If you do have to change the carrier I am sure there are YouTube videos. Get the tank as empty as possible and be prepared as it will still drain fuel on the floor. I have had mine out a few times and end up with just enough full to get to the station when done.

 

[Nodzed]

To test the gauge you don't open the tank so it doesn't matter. Jumping the wires is just touching them together with another wire. You are literally creating the circuit by connecting the wirings and removing the connection. The gauge will not act fast so you will have to keep them connected for a bit.

If you do have to change the carrier I am sure there are YouTube videos. Get the tank as empty as possible and be prepared as it will still drain fuel on the floor. I have had mine out a few times and end up with just enough full to get to the station when done.

You don't need to put power to the sender to check the gauge. If you drain the tank you won't get any spillage when you remove the pump and sender! If you do you haven't drained the tank enough.

 

[Delk]

You don't need to put power to the sender to check the gauge. If you drain the tank you won't get any spillage when you remove the pump and sender! If you do you haven't drained the tank enough.

How do you drain the tank?

 

[ExMX5owner]

@donutholer , If your lucky you will find as I did when I removed my sender, that a little plastic lug that holds the unit together and the contact brushes in place had somehow un-clipped itself and the brush was only contacting the resistance plate for part of its travel, and the guage topped out at 1/4 as yours has. clipped it back in place and not an issue since. But the guage is sloowwww to react to any change in fuel level, but Im told this is normal behaviour...

If you have to remove the sender, its like pulling a rabbit out of a hat, and when you go to replace it either with a new one or the same one , its like putting the rabbit back it the hat but with its arms and legs sticking out in all all over the place . So its a good idea to mark the orientation of the unit to avoid potential problems later... I Siphoned my tank pretty much dry, with a very flexible 5/16 hose to avoid possible damage to the sender, and had no issues with fuel spillage, although it took a while..

 

[donutholer]

You can do a gauge test using the dash buttons. If that's OK it's the sender, no need for jump cables to check the gauge. You buy a new pump and sender for the Z3, not long got one.

i'll look into doing a guage test. pump and sender is one part correct? usually on ebay

 

[bonbon]

There are a wide range of mishaps with the Z3 fuel gauge (search online for exhaustive threads on this issue) but your symptoms seem like the simplest failure so before doing anything drastic:
I just topped up a tank and the gauge read close to empty. I figured the computer resistance levels got screwed up. Disconnected the battery for 5 minutes and it’s now fine.
So now had all possible fuel gauge issues… to be expected at 475,000 km (probably the #1 problem on the Z3 - close race with the fan resistor bank).

 

[luis98bmwz3]

Recently purchased 1999 bmw z3 2.5l

second time filling the gas, after starting the car the fuel gauge was still marking on empty. Drove a bit and it climbed and now its right above the 1/4 marker.
Tried replacing the fuses per some posts but no luck.

I purchased some chevron high mileage fuel cleaner to poor into the tank when I'm guessing the tank is close to empty. Right now no idea what its at lol.

I saw there is a pretty bad issue with the fuel sensor in the tank, but seems like a really expensive fix, and also that little piece is a bit hard to find. Any other fixes I should try before replacing that sensor?

I have kinda the same issue, sometimes the gauge indicates that the fuel tank is full and after some driving it indicates like 3/4 full then goes back to full tank.

 

[ExMX5owner]

to be expected at 475,000 km

And I thought mine was doing well at 250k . If it wasn't my beloved Z I would have moved it on at 100k or so... Thinking of that, anyone interested in a Ford Ranger 4x4 , only ever driven by a sports car nut. Mostly off road towing caravans, launching boats, been swimming a few times and occasionally airborne, open to offers...

 

[donutholer]

There are a wide range of mishaps with the Z3 fuel gauge (search online for exhaustive threads on this issue) but your symptoms seem like the simplest failure so before doing anything drastic:
I just topped up a tank and the gauge read close to empty. I figured the computer resistance levels got screwed up. Disconnected the battery for 5 minutes and it’s now fine.
So now had all possible fuel gauge issues… to be expected at 475,000 km (probably the #1 problem on the Z3 - close race with the fan resistor bank).

unfortunately this didn't fix it.

another issue im having that im working on fixing is a parasitic drain on the car. So actually the car was dead for a couple days before I put a new battery in and the gauge is still showing empty. Previously it was 1/3rd of the way after filling the tank, but now just with the orange empty light.

 

[donutholer]

@donutholer , If your lucky you will find as I did when I removed my sender, that a little plastic lug that holds the unit together and the contact brushes in place had somehow un-clipped itself and the brush was only contacting the resistance plate for part of its travel, and the guage topped out at 1/4 as yours has. clipped it back in place and not an issue since. But the guage is sloowwww to react to any change in fuel level, but Im told this is normal behaviour...

If you have to remove the sender, its like pulling a rabbit out of a hat, and when you go to replace it either with a new one or the same one , its like putting the rabbit back it the hat but with its arms and legs sticking out in all all over the place . So its a good idea to mark the orientation of the unit to avoid potential problems later... I Siphoned my tank pretty much dry, with a very flexible 5/16 hose to avoid possible damage to the sender, and had no issues with fuel spillage, although it took a while..

Ok, I'll definitely take a look at the sender before buying a new one. I'm not sure how much gas is in my tank now, probably a bit less than half. How empty does it need to be to remove the sender without spilling any gas in the car?

 

[ExMX5owner]

Ok, I'll definitely take a look at the sender before buying a new one. I'm not sure how much gas is in my tank now, probably a bit less than half. How empty does it need to be to remove the sender without spilling any gas in the car?

That question, I'm not sure of. I could tell that my sender had been out before because the the orientation of the unit was wrong when I removed it or my driving on a semi full tank, and possibly was the cause of a subsequent issue, but the way I did it was a small flexible hose about 3/8 ID with a nut on the end, threaded on so it could not fall off into the tank, and siphoned it out, when I pulled the rubber out from around the sender unit, the fuel level was well below it, but if as your removing gently the big rubber grommet you see seepage, there is to much fuel left in the tank, push it back and do it again.. blow into the siphon , if you hear bubbles it will work, hold the hose above the tank, and suck as the fuel comes to the mouth stop sucking before you get a gob full and the thumb over to stop it going back. drop the end into into a suitable container lower than the car remove thumb and wait .. NO SMOKING... . I dont like playing with fuel, I just used what I had down here in antipodes, you guys up there might have some high tech device for sucking out fuel...

And I repeat, mark the orientation so it goes beck in the same way it came out...

 

[donutholer]

this is going to be an experience for sure. Thanks for all the tips, they're well appreciated!

That question, I'm not sure of. I could tell that my sender had been out before because the the orientation of the unit was wrong when I removed it or my driving on a semi full tank, and possibly was the cause of a subsequent issue, but the way I did it was a small flexible hose about 3/8 ID with a nut on the end, threaded on so it could not fall off into the tank, and siphoned it out, when I pulled the rubber out from around the sender unit, the fuel level was well below it, but if as your removing gently the big rubber grommet you see seepage, there is to much fuel left in the tank, push it back and do it again.. blow into the siphon , if you hear bubbles it will work, hold the hose above the tank, and suck as the fuel comes to the mouth stop sucking before you get a gob full and the thumb over to stop it going back. drop the end into into a suitable container lower than the car remove thumb and wait .. NO SMOKING...

And I repeat, mark the orientation so it goes beck in the same way it came out...

 

[bonbon]

You want to have less than a quarter of a tank. I would fill up and than drive 80% of your usual mileage.
There are exhaustive threads on this issue on the previous leading Zroadster site

 

[bonbon]

There are a wide range of mishaps with the Z3 fuel gauge (search online for exhaustive threads on this issue) but your symptoms seem like the simplest failure so before doing anything drastic:
I just topped up a tank and the gauge read close to empty. I figured the computer resistance levels got screwed up. Disconnected the battery for 5 minutes and it’s now fine.
So now had all possible fuel gauge issues… to be expected at 475,000 km (probably the #1 problem on the Z3 - close race with the fan resistor bank).

Just to update - it happened to me again - but this time decided to wait and it fixed itself to read correctly after 80 miles. Chinese gauge and topping up must send a false reading and takes a while to reset.

 

[donutholer]

Wanted to update on this issue. I drove it over to the gas station to fill it up as I had to move it to another garage. I filled it up, and went to reset the trip odometer to keep track of the tank, and lo and behold the gauge register as full. So potentially fixed ?

onto replacing the thermostat and replacing the exhaust!

 

[bonbon]

My lesson - don't top up. And if it goes wrong - wait a bit until it goes to below half a tank.
(That's not saying there aren't a host of other reasons that the most unreliable part is the Z3 can go wrong - tight competition with the OEM fan resistor pack)