What could cause a sticking fuel gauge - BMW 316i

[kinobestew123]

Hi everyone

Bought a 1993 E36 BMW 316i with 68k miles on the clock yesterday for Czecheap Challenge - driving to Prague to raise money for charity. I'll be putting up a post about this at some point but for now i'll stick to the problem.

If the fuel tank is full, the gauge will indicate that it is full. As the tank then empties, the gauge will follow it down to around half way. The next time the car is then started, the gauge will stay showing that the car is completely empty.

I'm guessing this is some kind of sensor issue but can anyone shed more detail including where the sensor is/how to fix it/anything else that could help us?

Thanks!

Stewart

 

[Bromhead]

Hey, good luck on your trip.

IIRC the fuel tank is below the back seats. When I had the issue a wire was broken inside the fuel tanks. But yep it was a sensor issue.

 

[kinobestew123]

Thanks Bromhead

I had a quick look last night and the fuel tank is indeed below the rear seats. From reading around online, it seems that it is going to be the fuel sender which is broken. It kind of looks like a piece of wire with a float on the end which floats on top of the fuel and swings up and down (like an old toilet ballcock).

It was too dark to start taking it out, but that is the plan for a spare weekend and i'll see if there is anything immediately obvious wrong with it, it may just need a clean to get any dirt out of the hinging part.

It looks like there may be one behind the passenger and one behind the driver? Does anyone know which one it is likely to be?

 

[geekman]

Definitely sounds like the fuel sender, my friend had the same problem on his E36. He managed to DIY fix it and isn't particularly mechanically competent so I'd imagine it's not that tricky.

 

[Dogbreath]

The "ballcock" arrangement moves a springy bit of metal (the 'wiper') over a resistance track, so the resistance varies with fuel level. Most often this kind of symptom is caused by the resistance track wearing out due to the constant rubbing motion of the wiper, so it goes open circuit once the level gets past a certain point. Most often the only fix is a new level sender, but sometimes you can bend the wiper to operate in a different part of the resistance track.

 

[Atari]

I'm pretty sure it'll be on the driver's side, should take about an hour if you're taking your time, likely less than though (I've seen an AA guy strip and refit one in my E46 in about 20 minutes). Complete new pump assemblies can be had from breakers for about £20-25 which may work out easier than trying to repair the current one.

 

[kinobestew123]

Awesome, thanks guys.

I'll get it taken out and see what I can see, i'll post up an update about my findings.

I'd say i'm fairly mechanically minded, replacing it and diagnosing it won't be a problem. I do however like to hear from other people who have experience so I can go straight to the right place, save time and take their tips on board. You guys have given me just the information I needed. Kudos!

Saying that, i'll be back if you're wrong

 

[Conscript]

Sticky fuel?

 

[Scania]

Sod the fuel guage, I'm more interested in the fact it's averaged 3,400 miles p/a over it's life!

My old e36 328i had a similar issue, turned out to be a bad earth.

 

[kinobestew123]

Sticky fuel?

It's funny you should say this, the guy who I bought it off informed me that he accidentally brimmed the tank with Diesel several years ago before having it all drained. Maybe sticky diesel is on the resistor.

Sod the fuel guage, I'm more interested in the fact it's averaged 3,400 miles p/a over it's life!

My old e36 328i had a similar issue, turned out to be a bad earth.

I know yeah, it's unbelievable isn't it really. The guy who I bought it off has owned many many cars over the years (he currently has 6 classics including a Vauxhall that i'm sure he said was near 100 years old!).