Fuel gauge

Need technical Q/A then you're in the right place

Moderator: martauto

Post Reply
User avatar
964russ
E30 Zone Newbie
E30 Zone Newbie
Posts: 144
Joined: Fri Jul 10, 2015 11:00 pm

Thu Jun 04, 2020 7:16 pm

Hi, trying to get this project finished.

The last "push".

Fuel gauge reads nothing, I've bridged the pump side and it reads half.

Is the pump side faulty or just the sender side?

Later car with pump on 1 side, just sender on other.

Fanks
BristolE30
E30 Zone Regular
E30 Zone Regular
Posts: 532
Joined: Thu May 16, 2019 7:43 pm
Location: Bristol

Fri Jun 05, 2020 12:24 pm

:mrgreen:
964russ wrote:
Thu Jun 04, 2020 7:16 pm
Hi, trying to get this project finished.

The last "push".

Fuel gauge reads nothing, I've bridged the pump side and it reads half.

Is the pump side faulty or just the sender side?

Later car with pump on 1 side, just sender on other.

Fanks
I’ve got the opposite problem, mine always reads full
BMW E30 316 ‘87
BMW E30 325i ‘88 :bmw:
Bristol, UK
capri_rob
Married to the E30 Zone
Married to the E30 Zone
Posts: 9681
Joined: Tue Feb 19, 2008 11:00 pm
Location: South Staffordshire

Fri Jun 05, 2020 6:26 pm

Following.
Last time I used mine it was flickering all over the place and then died.
The low fuel light still works but its now stuck on the bottom.
The MPG gauge is also intermittent im wondering if this could be linked to failed SI board batteries ?
Image

e30topless said : Proper BMW's have 4 headlights, last of the run was the E30 and E34/E32 anything after that is just complete shite
User avatar
Brianmoooore
E30 Zone Team Member
E30 Zone Team Member
Posts: 49358
Joined: Mon Jan 10, 2005 11:00 pm

Fri Jun 05, 2020 6:37 pm

964russ wrote:
Thu Jun 04, 2020 7:16 pm
Hi, trying to get this project finished.

The last "push".

Fuel gauge reads nothing, I've bridged the pump side and it reads half.

Is the pump side faulty or just the sender side?

Later car with pump on 1 side, just sender on other.

Fanks
RH sender is faulty (or the wiring to it). Possibly repairable.
User avatar
Brianmoooore
E30 Zone Team Member
E30 Zone Team Member
Posts: 49358
Joined: Mon Jan 10, 2005 11:00 pm

Fri Jun 05, 2020 6:40 pm

BristolE30 wrote:
Fri Jun 05, 2020 12:24 pm

I’ve got the opposite problem, mine always reads full
Even with the tank less then half full?
User avatar
Brianmoooore
E30 Zone Team Member
E30 Zone Team Member
Posts: 49358
Joined: Mon Jan 10, 2005 11:00 pm

Fri Jun 05, 2020 6:44 pm

capri_rob wrote:
Fri Jun 05, 2020 6:26 pm
Following.
Last time I used mine it was flickering all over the place and then died.
The low fuel light still works but its now stuck on the bottom.
The MPG gauge is also intermittent im wondering if this could be linked to failed SI board batteries ?
MPG gauge could be, but not normally the fuel gauge, unless the batteries have leaked really badly.
First test for the gauge is to bridge the sender wires at the pump assembly.
BristolE30
E30 Zone Regular
E30 Zone Regular
Posts: 532
Joined: Thu May 16, 2019 7:43 pm
Location: Bristol

Fri Jun 05, 2020 7:14 pm

Brianmoooore wrote:
Fri Jun 05, 2020 6:40 pm
BristolE30 wrote:
Fri Jun 05, 2020 12:24 pm

I’ve got the opposite problem, mine always reads full
Even with the tank less then half full?
Yes everytime I start her up it reads full for first 10 mins. Then sometimes it pings to correct reading
BMW E30 316 ‘87
BMW E30 325i ‘88 :bmw:
Bristol, UK
User avatar
964russ
E30 Zone Newbie
E30 Zone Newbie
Posts: 144
Joined: Fri Jul 10, 2015 11:00 pm

Sun Jun 07, 2020 12:29 am

Mine allways reads half.

Passenger side is bridged.

Before I bridged it there was no gauge.

Which side do I replace?

Drivers pump side or passenger sender (bridged 1)
User avatar
Brianmoooore
E30 Zone Team Member
E30 Zone Team Member
Posts: 49358
Joined: Mon Jan 10, 2005 11:00 pm

Mon Jun 08, 2020 2:15 pm

BristolE30 wrote:
Fri Jun 05, 2020 7:14 pm
Brianmoooore wrote:
Fri Jun 05, 2020 6:40 pm
BristolE30 wrote:
Fri Jun 05, 2020 12:24 pm

I’ve got the opposite problem, mine always reads full
Even with the tank less then half full?
Yes everytime I start her up it reads full for first 10 mins. Then sometimes it pings to correct reading
What happens if you pull the sender plug off at the fuel pump?
User avatar
Brianmoooore
E30 Zone Team Member
E30 Zone Team Member
Posts: 49358
Joined: Mon Jan 10, 2005 11:00 pm

Mon Jun 08, 2020 2:24 pm

964russ wrote:
Sun Jun 07, 2020 12:29 am
Mine allways reads half.

Passenger side is bridged.

Before I bridged it there was no gauge.

Which side do I replace?

Drivers pump side or passenger sender (bridged 1)
IF it ALWAYS reads half, then both sides are dud. LH one is open circuit, and RH one is stuck on empty.
What happens if you link out the RH one as well?
User avatar
Banban3
E30 Zone Newbie
E30 Zone Newbie
Posts: 18
Joined: Thu Sep 06, 2018 11:00 pm
Location: Paris, Fr

Wed Jun 10, 2020 10:04 am

BristolE30 wrote:
Fri Jun 05, 2020 7:14 pm
Brianmoooore wrote:
Fri Jun 05, 2020 6:40 pm
BristolE30 wrote:
Fri Jun 05, 2020 12:24 pm

I’ve got the opposite problem, mine always reads full
Even with the tank less then half full?
Yes everytime I start her up it reads full for first 10 mins. Then sometimes it pings to correct reading
I had the same issue. I opened the instrument cluster, took the fuel gauge out (one nut to remove) and cleaned the connection between the fuel gauge and the cluster itself, which is made by contact around the screw area (sorry if I don't have all technical terms, French here...).
This connection is the ground connection for the fuel gauge, as is illustrated in the electrical troubleshooting BMW document (that can be easily found on the web, and a great tool!). Then assembled everything again and working like a charm since. ;)

What happens is that since this connection is not working, then the current applied to the fuel gauge goes through the "full" position only (hence the "full" reading), nothing goes through the sensor loom. The sensor loom is the one that drags the indicator all the way between full to empy thanks to a variable resistor.
User avatar
Banban3
E30 Zone Newbie
E30 Zone Newbie
Posts: 18
Joined: Thu Sep 06, 2018 11:00 pm
Location: Paris, Fr

Wed Jun 10, 2020 10:14 am

Brianmoooore wrote:
Mon Jun 08, 2020 2:24 pm
964russ wrote:
Sun Jun 07, 2020 12:29 am
Mine allways reads half.

Passenger side is bridged.

Before I bridged it there was no gauge.

Which side do I replace?

Drivers pump side or passenger sender (bridged 1)
IF it ALWAYS reads half, then both sides are dud. LH one is open circuit, and RH one is stuck on empty.
What happens if you link out the RH one as well?
I agree that if it ALWAYS reads half, then both sides are faulty.

Passenger side for sure, since after bridging it, the gauge now gives a reading, so opting for a faulty sensor rather than a faulty wiring.

Under current wiring (passenger side bridged), if the reading moves (half to low) as fuel is used, then replacing the passenger side should do the trick. Otherwise, driver's side may be stuck in a specific position. Maybe worth taking it out and trying to unlock it. Otherwise, replacement.
User avatar
Banban3
E30 Zone Newbie
E30 Zone Newbie
Posts: 18
Joined: Thu Sep 06, 2018 11:00 pm
Location: Paris, Fr

Wed Jun 10, 2020 10:17 am

capri_rob wrote:
Fri Jun 05, 2020 6:26 pm
Following.
Last time I used mine it was flickering all over the place and then died.
The low fuel light still works but its now stuck on the bottom.
The MPG gauge is also intermittent im wondering if this could be linked to failed SI board batteries ?
The low fuel light working means the wiring is correct, this is just the display that is faulty, and highly likely this is a contact issue. As previously answered to another one, open the instrument cluster, take the fuel gauge out, clean the contact between the fuel gauge and the cluster, put everything back together and it should work.

For mpg, it may just be connections in the connectors at the back of the instrument cluster. I have new batteries on the SI board, and sometimes had same issue. I cleaned every contact at the back of the cluster, and now it is working fine.
User avatar
Brianmoooore
E30 Zone Team Member
E30 Zone Team Member
Posts: 49358
Joined: Mon Jan 10, 2005 11:00 pm

Wed Jun 10, 2020 10:53 am

Banban3 wrote:
Wed Jun 10, 2020 10:04 am

I had the same issue. I opened the instrument cluster, took the fuel gauge out (one nut to remove) and cleaned the connection between the fuel gauge and the cluster itself, which is made by contact around the screw area (sorry if I don't have all technical terms, French here...).
This connection is the ground connection for the fuel gauge, as is illustrated in the electrical troubleshooting BMW document (that can be easily found on the web, and a great tool!). Then assembled everything again and working like a charm since. ;)

What happens is that since this connection is not working, then the current applied to the fuel gauge goes through the "full" position only (hence the "full" reading), nothing goes through the sensor loom. The sensor loom is the one that drags the indicator all the way between full to empy thanks to a variable resistor.
Excellent English, an excellent description of exactly how the system works, and almost certainly an exact diagnosis of the problem in this case.
capri_rob
Married to the E30 Zone
Married to the E30 Zone
Posts: 9681
Joined: Tue Feb 19, 2008 11:00 pm
Location: South Staffordshire

Wed Jun 10, 2020 8:12 pm

Banban3 wrote:
Wed Jun 10, 2020 10:17 am
capri_rob wrote:
Fri Jun 05, 2020 6:26 pm
Following.
Last time I used mine it was flickering all over the place and then died.
The low fuel light still works but its now stuck on the bottom.
The MPG gauge is also intermittent im wondering if this could be linked to failed SI board batteries ?
The low fuel light working means the wiring is correct, this is just the display that is faulty, and highly likely this is a contact issue. As previously answered to another one, open the instrument cluster, take the fuel gauge out, clean the contact between the fuel gauge and the cluster, put everything back together and it should work.

For mpg, it may just be connections in the connectors at the back of the instrument cluster. I have new batteries on the SI board, and sometimes had same issue. I cleaned every contact at the back of the cluster, and now it is working fine.
Thankyou for this I will try this first and report back :D
Image

e30topless said : Proper BMW's have 4 headlights, last of the run was the E30 and E34/E32 anything after that is just complete shite
User avatar
Brianmoooore
E30 Zone Team Member
E30 Zone Team Member
Posts: 49358
Joined: Mon Jan 10, 2005 11:00 pm

Wed Jun 10, 2020 9:30 pm

Banban3 wrote:
Wed Jun 10, 2020 10:17 am
The low fuel light working means the wiring is correct,
Not so, I'm afraid. The wiring for the gauge and light is completely separate from each other, other than a common earth wire from the RH sender to the earth point on the LH side of the rear seat. Having said that, the wiring for either doesn't normally give trouble.
User avatar
Banban3
E30 Zone Newbie
E30 Zone Newbie
Posts: 18
Joined: Thu Sep 06, 2018 11:00 pm
Location: Paris, Fr

Thu Jun 11, 2020 9:09 am

Brianmoooore wrote:
Wed Jun 10, 2020 9:30 pm
Banban3 wrote:
Wed Jun 10, 2020 10:17 am
The low fuel light working means the wiring is correct,
Not so, I'm afraid. The wiring for the gauge and light is completely separate from each other, other than a common earth wire from the RH sender to the earth point on the LH side of the rear seat. Having said that, the wiring for either doesn't normally give trouble.
Yep, correct, went too fast! Thanks for the correction!

Low fuel is only on the pump side indeed.

Sorry for that, I had my issue in mind when everything worked fine (including low level) except the gauge itself (OBC fuel level was correct, so I knew the wiring was correct).

Thanks again for the correction. 🙂
User avatar
Banban3
E30 Zone Newbie
E30 Zone Newbie
Posts: 18
Joined: Thu Sep 06, 2018 11:00 pm
Location: Paris, Fr

Thu Jun 11, 2020 10:47 am

Giving it a second thought, based on Brian's correction, before tearing apart the instrument cluster, you may want to check the following continuities first, at the C2 connector (the white one on the back of the cluster). Make sure you check for high resistor values, to avoid false negative results (you are not looking for a simple wire continuity, but for continuity through resistors):
  • Since your low level light is working, you should have continuity between pins 6 and 5.
  • Then check continuity between pins 6 and 4 (full side of the gauge), and between pins 6 and 16 (empty side of the gauge).
    • If there is continuity for both combinations, then there should be no need to open the cluster and your issue is between pin 4 and the sensor on the RH side (other tests then to perform, such as bridging sensors).
    • If either combination does not show continuity, then you may want to clean the contact between the gauge and the cluster to ensure continuity first.
Diagram of the pins:
Sans titre.jpg
Diagram of the gauge:
Sans titre-2.jpg
(Edit: formatted so that it reads better)
Post Reply