gas gauge issues

[Kozworth]

WWhen i put 5 gallons in my tank i go from the gas light on to half tank. I thought this was wierd because the tank is a 16 gallon tank soi should get about a 1/3 tank. The gauge drops very quickly.

Also, i need help determining which fuel gauge is bad. The sending unit or the one on the fuel pump.


Is there a testing procedure for these parts?

[Cabriolet]

same here, mostly likely its the lever senders have gone bad. i just use the trip mileage and fill up every 200 miles.
@ $122.00 each im not replacing mine.

[Kozworth]

Seems bad to me. But its very hard for me to determine how much mileage i really am getting.

Obc claims 20mpg but im not totally sure what it really is. I figured its probably working off a resistive strip, and as the tank drops it sends a different voltage to let the gauge know where its at. But everywhere in the bentley seemed to have seldom info on the sending unit.

Which gets to my other question. Since the tank seems to have a slope up for the driveshaft, how does the gas on the drivers side of the driveshaft make it over to the pump?

[nando]

you either have a level sensor/gauge mismatch, or something's gone bad.

a simple thing to do would be to check the grounding nut on the back of the cluster to see if it's come loose.

also it would be helpful to know what car you have, different E30s have different sensor/gauge combinations.

[stamar]

Ya theres a grounding nut on the back of the cluster that often corrodes.

needs filing.

If you have the capacity still working in the obc the tank sensor is still working.

I have this same problem. It often shows half full whether its full or empty. However, the light still works when its near empty.

I want to give you a 75% 25% chance that its the gage itself causing the problem based on what you said.

Theres a youtube video showing where to clean up. Theres one on each side, the other one is for the temperature gauge. Take a look at e30 forums for threads asking for help with a wandering temperature gauge or a gauge that gets worse when you hit a bump.

the gauge behaves the same. For some reason unknown the temperature guage fails like this more commonly than the gas guage but they are wired in the cluster exactly the same way.

[Gregs///M]

The senders inside the tank might need to be cleaned. Its a simple process once the pump is removed from the tank

[Kozworth]

The car is an 88 325is intake pump.

I know the one on the pump seems to move freeley, you can hear the element move. As for the sending unit, how does that one get cleaned?

I will check the back of the cluster.

For example today, 5 gallons got me from gas light to full. After 20 miles the needle was on about 30% of a tank left.. the obc has been more or less my nonstressful guide. Since the tank should be 16 gal, it should read a little over the 1/4 mark with 5 gallons in, and not half a tank.

Im also still looking for an answer on how does the tank cycle the fuel from the drivers side of the tank to the passenger side. If there isnt a pump on the drivers side, and the passenger side pump isnt connected to the drivers side, how does the gasoline transfer to the passengerside? looks like there is a line that is run inside the tank, but since my old tank is trashed i might cut it up to find out

[toointoxicated60]

Sounds like you have a 318 gauge in there assuming you have 325i. I had swapped in a euro 318 cluster and the gas gauge was way off..

[Kozworth]

Sounds like you have a 318 gauge in there assuming you have 325i. I had swapped in a euro 318 cluster and the gas gauge was way off..

As far as I know this cluster is still original, even then so, the smaller tank was 14gallons and still would not give me 1/2 a tank when I only put 5 gallons in.

[toointoxicated60]

They had completely different sensors. i believe the 325's had a separate sensor and the 318's had sensors attached to the fuel pump assembly.

[Kozworth]

They had completely different sensors. i believe the 325's had a separate sensor and the 318's had sensors attached to the fuel pump assembly.

From what I understand, the 325 has a "Sending Unit" which is a sensor, and also a built in sensor attached to the fuel pump. This one is bolted with 4 8mm bolts. Atleast, thats what ive had since I had the car.

I do not understand why there would be a need for two fuel gauge sensors... And everywhere Ive read hasnt specified the reason why eithor..

[toointoxicated60]

318 and 325 sensor and gauges are different. The gas tanks are different.

318/m3 has a gas tank with a single hole. The fuel level sensor and pump are on the same assembly.


325 have a separate fuel level sensor. Its on the right on the attached photo. Fuel pump is on the left.


The fuel level sensors are different and not interchangeable same with the gauges. The sensors have different OHM values when full/empty. Mismatch gauge and sensors would cause the issue you described.

[Kozworth]

Then on the 325 tank what is the thing connected to the pump? Its got the 4 bolts.

Because I swapped pumps, and that thing was clogged.. and I ran out of gas when It said I had 1/4 tank. And when I swapped that, then my gas gauge returned to actually being somewhat right.

So from what I have experienced, both that piece bolted into the fuel pump and the sending on the right side of the tank seem to measure gas level.

Please correct me if I am overthinking this, but from what I see two fuel level sensors.

[nando]

It's a level sensor. facelift cars have 2, except the 318is, which only has one.

[stamar]

From what I understand, the 325 has a "Sending Unit" which is a sensor, and also a built in sensor attached to the fuel pump. This one is bolted with 4 8mm bolts. Atleast, thats what ive had since I had the car.

I do not understand why there would be a need for two fuel gauge sensors... And everywhere Ive read hasnt specified the reason why eithor..

Im almost sure one is for the fuel guage, and one is for the empty light at 2 gallons.

seperate.

does a 318 not have an empty light? even if it does, it goes from the same sender obviously.