Gas guage on the fritz!!!

[RVAe30]

so my gas guage started acting really weird last weekend, i drove to the mall to return some shit and everything was doing just great in the 325i. I turn my car on to leave and i notice my gas guage is acting weird. It is jumping around erratically. I thought it might go away because my temp guage does it sometimes aswell, but never for an extended period of time.

it doesnt go away. I fill up the tank to drive back to school, thinking that some gas in the tank might do something. Nope not at all. Now it doesnt really move as much. It just goes from just above half a tank to all the way full.

Has anyone ever experienced this before? electrical probably? if so anyone know how or where this problem is fixed/located?

thanks everyone I appreciate it.


EDIT: i searched and another thread said to take out the cluster and tighten the nut in back of the guage.

[Mike325]

It may be your level sensor in the tank. You could also have a bad ground or a loose wire somewhere. You can try a few things to see what the problem is.

1: Get your tank to about half full.
2: Get on one side of the car with the key on and move up and down to get the car shaking from side to side. See if the level changes.
Or.....

1: Take the plug off of the level sensor (on top of the tank) and put a meter on the ends on the sensor its self. Then do the same thing. See if the voltage changes as you bounce up and down. This will simulate changing fuel levels and the voltage should change as you bounce around. If the voltage does not change much, then the sensor could be the problem.

[RVAe30]

will do, thanks

[silversleeper]

my temp gauge acts up like that. its almost as if the thing is too weak/worn to stay steady anymore. temp gauge normally sits a little before halfway position, and a even halfway when idling in traffic.when it hits 50% of the gauge, it drops to the 3/4 mark and struggles to go back to the center, or drops to the 1/4 mark and struggles to get to center again. i just freak out everytime i see it "appear" to run hot, but then calm down once it jumps back to center again.

[Mike325]

My temp does the same thing. It does not slowly go up, just jumps from one spot to the next.

[silversleeper]

My temp does the same thing. It does not slowly go up, just jumps from one spot to the next.

yeah, mine jumps as well, no gradual/normal movement.

[Jean]

It may be your level sensor in the tank. You could also have a bad ground or a loose wire somewhere. You can try a few things to see what the problem is.

1: Get your tank to about half full.
2: Get on one side of the car with the key on and move up and down to get the car shaking from side to side. See if the level changes.
Or.....

1: Take the plug off of the level sensor (on top of the tank) and put a meter on the ends on the sensor its self. Then do the same thing. See if the voltage changes as you bounce up and down. This will simulate changing fuel levels and the voltage should change as you bounce around. If the voltage does not change much, then the sensor could be the problem.

Small correction, fuel lever sender does not generate any voltage . Think of it as a potentiometer, it varies in resistance depending on where the "float" inside the sender is.

[BigD]

my temp gauge acts up like that. its almost as if the thing is too weak/worn to stay steady anymore. temp gauge normally sits a little before halfway position, and a even halfway when idling in traffic.when it hits 50% of the gauge, it drops to the 3/4 mark and struggles to go back to the center, or drops to the 1/4 mark and struggles to get to center again. i just freak out everytime i see it "appear" to run hot, but then calm down once it jumps back to center again.

A firm fist to the dash fixes that every time.

[jlevie]

A common cause of an erratic fuel and/or temp gauge is deformation of the solder where the gauge mounting studs contact the main PCB in the cluster. A fix is to remove & disassemble the cluster and re-flow the solder pads for those gauges.

[silversleeper]

A common cause of an erratic fuel and/or temp gauge is deformation of the solder where the gauge mounting studs contact the main PCB in the cluster. A fix is to remove & disassemble the cluster and re-flow the solder pads for those gauges.

if i ever get around to painting my gauge needles red, i will definitely look into doing that. kinda like refurbishing the gauge cluster. thanks!

[Mike325]

Small correction, fuel lever sender does not generate any voltage . Think of it as a potentiometer, it varies in resistance depending on where the "float" inside the sender is.

Yep, your right. Thanks for the correction. Set your meter to ohms.

[RVAe30]

1: Get your tank to about half full.
2: Get on one side of the car with the key on and move up and down to get the car shaking from side to side. See if the level changes.

nothing.

1: Take the plug off of the level sensor (on top of the tank) and put a meter on the ends on the sensor its self. Then do the same thing. See if the voltage changes as you bounce up and down. This will simulate changing fuel levels and the voltage should change as you bounce around. If the voltage does not change much, then the sensor could be the problem.

ill try testing it when i get home for spring break. thnks guys

[xLibelle]

rocking the fuel in the tank to test the level sensor is dumb.
just pull the seat, the cover and the 4 nuts to the sensor.
pull the sensor out and put an ohm meter across the lines.
one of them is ground, middle is level, and other is refuel.
read meter while tipping sensor as the float moves around.
if i was reading my shit analog meter correctly, you should see 40-750 ohm
but this description of a problem is not commonly a sensor fault


obvious answer can be an intermittent short somewhere between sensor and cluster

but question is, does the fuel level touch the SI board? because many sensor reading problems can be attributed to the board's battery going dead.

[Mike325]

rocking the fuel in the tank to test the level sensor is dumb.

No it not:D

[xLibelle]

i was searching for troubleshooting info on this topic - my guage would never read anything above 1/3 tank.
checked the sensor that sits with the pump, everything ok.
by having searched the site, i came to find that theres a second sensor. well damn.
pulled it appart and it was stuck. it somehow gained a knick in the wire (it was sitting for almost a year w/o fuel level change). Picture taken at wrong angle to show hump.

but when fuel is forced to one side or another, the two sensors normalize the guage reading.