Fuel Gauge inaccurate, but fun!

[Been-Jammin]

I noticed that I was approaching empty the other day and didn't remember using all that much fuel. When I went to fill up, the pump stopped at 7 gallons. Thinking it was due to back pressure, I pulled the handle out slightly and filled some more. About 1/4 gal and it would not take any more fuel. Stubbornly thinking, I tried again and ended up overflowing. Hmmm.

After pulling out of the gas station I noticed that I only had a half tank. Thinking to myself... Why would the tank only fill half way up? Was there a balloon in the tank taking up space? Was there a fuel pressure issue which was making the fuel bubble out of the tank? Probably not. After a few miles I noticed that I only had a 1/4 tank. Wow! What a guzzler!!! I stopped to check for leaks. Didn't see or smell any fuel. So I started up and behold, I had a half tank again! Like a visit from the gas fairy. This went on all day, each time I stopped, shut the car off and started up again, the tank would fill back up to 1/2 then rapidly drop down to empty. I thought to myself again, if this were only real! I could simply stop and wish for more fuel and wahoo! More fuel!

Then reality kicked in. I have a faulty fuel gauge system. So the question is, What's going bad, the sending unit in the tank or the gauge in the dash? I've seen where the capacitors go bad, but before I go ripping the dash out, I'd like to make sure that is the culprit.

Has anyone had a similar problem with the fuel gauge?
If so, what was the fix?

Thanks!

[632 Regal]

sure the tank hasnt caved in from vacumme? Not that uncommon a thing.

Just my 2¢ which is now worth 1/2 cent with the devaluation of the US dollar.

[McWatters]

my gas gauge is very odd aswell, likes to sit at the 1/4 mark

and bounces around like a nutter everyonce and a while.


cheers

J.McWatters

[Kalevera]

check the sending unit first.

We picked up a 750iL for a grand on ebay. Guy claimed it wouldn't start due to an electrical fire. We checked the harness and one non critical item was burned.

Albeit the fuel gauge read half a tank, removing the pump indicated that, in fact, the car was just out of gas.

Car now has gas and runs as one of our loaners.

best, whit

[pundit]

I noticed that I was approaching empty the other day and didn't remember using all that much fuel. When I went to fill up, the pump stopped at 7 gallons. Thinking it was due to back pressure, I pulled the handle out slightly and filled some more. About 1/4 gal and it would not take any more fuel. Stubbornly thinking, I tried again and ended up overflowing. Hmmm.

After pulling out of the gas station I noticed that I only had a half tank. Thinking to myself... Why would the tank only fill half way up? Was there a balloon in the tank taking up space? Was there a fuel pressure issue which was making the fuel bubble out of the tank? Probably not. After a few miles I noticed that I only had a 1/4 tank. Wow! What a guzzler!!! I stopped to check for leaks. Didn't see or smell any fuel. So I started up and behold, I had a half tank again! Like a visit from the gas fairy. This went on all day, each time I stopped, shut the car off and started up again, the tank would fill back up to 1/2 then rapidly drop down to empty. I thought to myself again, if this were only real! I could simply stop and wish for more fuel and wahoo! More fuel!

Then reality kicked in. I have a faulty fuel gauge system. So the question is, What's going bad, the sending unit in the tank or the gauge in the dash? I've seen where the capacitors go bad, but before I go ripping the dash out, I'd like to make sure that is the culprit.

Has anyone had a similar problem with the fuel gauge?
If so, what was the fix?

Thanks!

When you think of E34 idiosynchrosies include inaccurate fuel gauge.
Once mine gets below about one half to a third full you may as well forget it.
By the time it gets to a quarter it can suddenly drop to zero, then the low fuel light comes on. Next time I look at it it's back up to quarter again.
I tried cleaning the wire resistor and wiper on the sender unit but it made no difference. It appears the bottom part of the plastic housing tube that contains the sender mechanism tends to crack around the nut on the end of the rod that supports and centralises the float causing the float to foul against the housing tube. The float doesn't begin to foul until the tank gets to below about half full. I can't really see an easy way to reliably repair this as you would need some kind of glue that was not effect by the fuel.

[Dan in NZ]

WOW! I thought mine was unique! It's pretty accurate between 20-80L, but between R-20 it's all over the place. It can be sitting on empty for a week, then you fill it up and it only takes 65L or so. I find that the Range is more accurate than the fuel guage.

[uscharalph]

When you think of E34 idiosynchrosies include inaccurate fuel gauge.
Once mine gets below about one half to a third full you may as well forget it.
By the time it gets to a quarter it can suddenly drop to zero, then the low fuel light comes on. Next time I look at it it's back up to quarter again.
I tried cleaning the wire resistor and wiper on the sender unit but it made no difference. It appears the bottom part of the plastic housing tube that contains the sender mechanism tends to crack around the nut on the end of the rod that supports and centralises the float causing the float to foul against the housing tube. The float doesn't begin to foul until the tank gets to below about half full. I can't really see an easy way to reliably repair this as you would need some kind of glue that was not effect by the fuel.
Mine is fine till it gets to 1/4 tank, then is likes to bounce around to empty and back. I've found that the range on the OBC is pretty accurate though as a backup,

[uscharalph]

Mine is fine till it gets to 1/4 tank, then is likes to bounce around to empty and back. I've found that the range on the OBC is pretty accurate though as a backup,
I used to just bang on the dash and the needle would return to where it should be, but I stopped doing that. I don't thinks it's good for the instrument cluster. The other night the digital odometer went out, until I banged on it again. I'll just rely on the range on the OBC for now.

[guinness]

Mine is just lazy, when I start her up the guage barely moves, but within about 2 min it shows the proper level.

[Been-Jammin]

sure the tank hasnt caved in from vacumme? Not that uncommon a thing.

Just my 2¢ which is now worth 1/2 cent with the devaluation of the US dollar.


I've never heard of such a thing, but I will certainly have a look when I check out replacing the sending unit. ;)

[genphreak]

Mine works fine, I swear its fastest from 80-60, and slowest from 40-0. Suits me just fine... the bouncing gauge is probaly faulty cluster connections, earths... perhaps it could be created by poorly connected accessories... car-kits, stereos et al. :) GP

[Been-Jammin]

Today... 3/4 tank for 8 gallons off of the zero mark... Perhaps the tank is shrinking... :p

[632 Regal]

mine works great, 100 miles per 1/4 tank all the way to empty...very accurate.

[Been-Jammin]

mine works great, 100 miles per 1/4 tank all the way to empty...very accurate.

Same with the gauge on my last 530i, never a problem.
This car sat in a garage alot though, was owned by a snowbird. So I can imagine the sending unit just got used to sitting at 1/2 tank... Or sitting in any one position. I'm assuming there's a rheostat attatched to a float and sitting in one position is not healthy for a rheostat. ;)

[Dave M]

Mine has been bottom heavy since the day I got her. It'll sit between R-40 for 100s of kms, then the range will sit @100km for another 100km before the low fuel light illuminates. On my last stage of my recent road trip I recorded over 1000km and the range still gives me 110km. 7.4 L/100km (@32mpg) with low comp in #5, not bad.

Definitely an e34 quirk,

Dave M