Typical, but not quite typical 'Fuel Gauge not Working' post.

[2002Scoob]

Hey Guys,

 

I'm running out of random projects to try to do with my car while POS slow as hell mechanic should hopefully be delivering a corrected and finished build of my cylinder head. But that's not the point of this post.

 

One thing I tried to remedy a while ago, and never quite got right was fixing my non-functioning fuel gauge. When I first bought my car the gauge was not working, so I got used to refilling at a set interval.

 

After some trouble shooting it looks as though the gauge pack is grounded properly, I pulled the fuel sending unit.

 

It WAS an open style (no metal tube surrounding) unit with 3 spaded contacts. I went onto eBay and ordered a new unit from a seller in Greece that was supposed to be a 3 connection sender of the correct type, but he ended up sending me a 2-terminal enclosed tube style unit. From my understanding, the 3rd. terminal is for a low fuel level light, and the seller was uncooperative about getting a replacement, so I resigned myself to to trying to make it work.

 

But it doesn't. 

 

When connected, it still reads as empty, regardless of fuel level, and if you reverse polarity, the gauge jumps to 'full', so I can assume the gauge itself is working properly.

 

All I can assume is that perhaps the sending unit I have is not the same or proper resistance for the gauge, or perhaps there's something to having that 3rd contact connected to something.

 

Anybody have any thoughts? Is the a solution as simple as splicing in a resistor or something into the line.

 

I hate dealing with electrical... hah

 

This is a quick photo I took a few years ago when I put in the new unit. The old unit had 3. Shortly after taking this photo I replaced all the fuel lines in the trunk + a new fuel pump. The little plastic fitting was split and needed to be replaced, so it was leaking. 

 

 

[JDTable]

Sorry I won't be of much help to getting the sending unit you have working, but is this what your old one looked like? This one is enclosed. If so let me know if you need any measurements taken or any info on it.

 

 

 

Sent from my LGLS991 using Tapatalk

 

 

 

 

[2002Scoob]

My old one was lacking the metal tube.

 

The more I research I'm thinking there's no such thing as a 'tubeless' version.

 

My guess?- The sending unit failed (broken resistor wire) and the previous owner took it apart, discovered it, and then maybe didn't even bother to reassemble and threw it right back into the tank as-is. 

 

 

[JDTable]

I have a tube-less one on my '79 320i but it only had 2 leads my plan was to replace it with this one I just got pictured above and just seal the tube but looks like I'll run into the similar issues

Sent from my LGLS991 using Tapatalk

[John76]

The two-wire sender on my '76 gives 4 ohm resistance (between the terminals) when the tank is full, and 80 ohms when empty.

Just hold the sender in your hand and rotate. You should be able to hear the float slide back and forth on the wire inside the tube.

I get the following readings:  Full = 4 ohms, 3/4 = 23 ohms, 1/2 = 42 ohms, 1/4 = 61 ohms and Empty = 80 ohms.

After checking the sender, find a resistor to connect between the brown/yellow wire and the brown (ground) wire. When the ignition is switched on, you should see the gauge on your instrument panel read the appropriate level.

NOTE: Be sure your ground wire is good. If it is not solid, the fuel gauge will bounce when you use the right turn signal!

[02Les]

Not sure this will help you, but.........You should have an enclosed 3 connector sending unit like Juan's picture. However, your 2 connector one should (in theory) work but you would be, as you assumed, missing the low fuel warning.

The terminal next to the outlet pipe is the ground (solid brown wire) and should be connected to the trunk floor. The wire that goes directly to the fuel gauge in the cluster is brown-yellow. The 3rd wire (brown-black) is for the low fuel warning (red light in cluster). Not sure if it matters which of the double terminals has the br-bl or the br-yellow wire. Pic below is how mine was connected before I stripped the car for refurb.

[02Les]

26 minutes ago, 2002Scoob said:

My old one was lacking the metal tube.

 

The more I research I'm thinking there's no such thing as a 'tubeless' version.

 

My guess?- The sending unit failed (broken resistor wire) and the previous owner took it apart, discovered it, and then maybe didn't even bother to reassemble and threw it right back into the tank as-is. 

 

 

When I removed my sending unit (the one in the pic in my post below) the filter at the bottom of the unit had fallen off and the tube had slipped down to rest on the bottom of the tank. It did still work though. There's not much holding these things together.

[2002Scoob]

Soooo... I'm digging this guy back up from the dead, as my weekend project is to see whats up with the fuel sending unit/gauge on my 02. 

 

Chime in. Follow along. Tell me I'm an Idiot  Hopefully I figure it out!

[2002Scoob]

My plan of action-

 

1.Fill up the tank to the brim. 

2. Steal voltage/resistance meter from the shop at work

3. Measure resistance at the tank at  full

4. Remove Sending Unit, measure resistance at the tank when the slide-y thing should be bottomed out in the tube.

 

If there different, Good.  (I need to do some googling to figure out what the reading should be at full/empty) And i need to look to my gauge-pack, although that was nicely grounded before. 

 

If they're the same, then I'll be tearing apart the sending unit to make sure that slide-y thing is being a slide-y thing and not a stuck thing, and the resistance wire is intact. 

 

Currently when plugged in, my gauge reads "full" all the time, no matter what.

 

Whereas, before I installed the new sending unit, it just read empty because the sending unit that came with my car was essentially just in pieces floating around the tank.

 

 

[2002Scoob]

On 3/12/2017 at 6:23 PM, John76 said:

I get the following readings:  Full = 4 ohms, 3/4 = 23 ohms, 1/2 = 42 ohms, 1/4 = 61 ohms and Empty = 80 ohms.

 THis is what I was lookin for! Here all along Thanks John

[MatthewCervi]

3 hours ago, 2002Scoob said:

My plan of action-

 

1.Fill up the tank to the brim. 

2. Steal voltage/resistance meter from the shop at work

3. Measure resistance at the tank at  full

4. Remove Sending Unit, measure resistance at the tank when the slide-y thing should be bottomed out in the tube.

 

If there different, Good.  (I need to do some googling to figure out what the reading should be at full/empty) And i need to look to my gauge-pack, although that was nicely grounded before. 

 

If they're the same, then I'll be tearing apart the sending unit to make sure that slide-y thing is being a slide-y thing and not a stuck thing, and the resistance wire is intact. 

 

Currently when plugged in, my gauge reads "full" all the time, no matter what.

 

Whereas, before I installed the new sending unit, it just read empty because the sending unit that came with my car was essentially just in pieces floating around the tank.

 

 

 

I would not fill the tank up if you're planning on removing the sender--you'll spill a lot of gas when you pull it out.  Like John76 said, just pull it out and rotate it to simulate the different levels of the tank (at a minimum you'll be able to simulate full and empty).

 

Are you certain you have the correct wires hooked up to the sender?  The "reverse polarity" results don't make sense because the resistor wire is just a path to ground.  It shouldn't matter which way the current flows through the wire.

[2002Scoob]

You know those times when you feel like a complete idiot? This is one of them.


Sent from my iPhone using Tapatalk

[2002Scoob]

Soooo. When you buy a new sending unit, they logically and intelligently include a little wire clip that locks the float from bouncing around in shipment.



Guess what doofus didn't remove it.

However, you do get to different readings depending on the polarity.

Best fix ever


Sent from my iPhone using Tapatalk

[Son of Marty]

Doh !!!!!!

[2002Scoob]

The funny thing is... I remember when I installed it I thought, why would they put this stupid ass wire on here, it makes it a PITA to get it into the tank. 

 

And upon un-installing it today that same dumb wire got caught and i thought, that stupid thing... why would they do that.