My Fuel Gauge has tourettes...

OCCoupe

OCCoupe

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Please nothing against folks that suffer from tourettes.

I have a '73 3.0CS, my fuel gauge was working properly when all of the sudden it decided to become spastic and jump all over the place usually settling for the 1/5th point but only for a moment then it starts its spastic movement again. It is so extreme that I can hear it bouncing and striking both extremes of the gauge. It behaves the same on a full mid and empty tank. I tried searching the forum; but couldn't find anything.

Any thoughts or suggestions would be highly appreciated.

Thank you,
Mike
 
Please nothing against folks that suffer from tourettes.

I have a '73 3.0CS, my fuel gauge was working properly when all of the sudden it decided to become spastic and jump all over the place usually settling for the 1/5th point but only for a moment then it starts its spastic movement again. It is so extreme that I can hear it bouncing and striking both extremes of the gauge. It behaves the same on a full mid and empty tank. I tried searching the forum; but couldn't find anything.

Any thoughts or suggestions would be highly appreciated.

Thank you,
Mike
 
Mike,

I had this problem on my 3.0S many years ago. The fuel level sensor has a little float that travels up and down on a post making contact (left and right) with a resistive wire that runs from the top to the bottom and then back to the top. When the fuel level is high the float will be at the top creating a low resistance path and when it is at the bottom the resistance it at the maximum level. Also, when the float reaches the bottom is closes contacts that turn on the low fuel level display. This entire assembly is houses in an aluminum tube with a small hole at the bottom and a plastic bottom cover; the small hole creates a sort of low pass filter to prevent rapid changes in the float level. There are three wires connected on the top: ground, level sensor, and low fuel sensor. The sensor assembly can be removed by giving it a 1/16 counter clockwise rotation and then lifting. Be advised though that when you take it out there is a rubber O-ring under it that loves to leak when re-installed and this will create a wonderful fuel aroma in your cabin.

In your case there are a few things that come to mind:

1. It could be a loose connection but this doesn't explain why the gauge goes to 1/15th - I suspect an open circuit would produce a "full" level.

2. The plastic bottom cover has come loose. This is the problem that I had. Basically the nut came off the bottom and the plastic cover fell off and the aluminum cover was clanking around and causing problems like you describe.

3. The sensor wire has broken. I managed to break mine when I tried to remove the assembly with the flopping metal shroud. It is extremely hard to repair this wire but I was able to do it.

I think I may have an extra fuel sensor assembly in my supply of spare parts if you need one. This is assembly is also used on the 3.0S / Bavaria family so they should be available on the used market with some searching.
 
Mike,

I had this problem on my 3.0S many years ago. The fuel level sensor has a little float that travels up and down on a post making contact (left and right) with a resistive wire that runs from the top to the bottom and then back to the top. When the fuel level is high the float will be at the top creating a low resistance path and when it is at the bottom the resistance it at the maximum level. Also, when the float reaches the bottom is closes contacts that turn on the low fuel level display. This entire assembly is houses in an aluminum tube with a small hole at the bottom and a plastic bottom cover; the small hole creates a sort of low pass filter to prevent rapid changes in the float level. There are three wires connected on the top: ground, level sensor, and low fuel sensor. The sensor assembly can be removed by giving it a 1/16 counter clockwise rotation and then lifting. Be advised though that when you take it out there is a rubber O-ring under it that loves to leak when re-installed and this will create a wonderful fuel aroma in your cabin.

In your case there are a few things that come to mind:

1. It could be a loose connection but this doesn't explain why the gauge goes to 1/15th - I suspect an open circuit would produce a "full" level.

2. The plastic bottom cover has come loose. This is the problem that I had. Basically the nut came off the bottom and the plastic cover fell off and the aluminum cover was clanking around and causing problems like you describe.

3. The sensor wire has broken. I managed to break mine when I tried to remove the assembly with the flopping metal shroud. It is extremely hard to repair this wire but I was able to do it.

I think I may have an extra fuel sensor assembly in my supply of spare parts if you need one. This is assembly is also used on the 3.0S / Bavaria family so they should be available on the used market with some searching.
 
Thanks JJ, I'll see if I have time to pull the unit out of the tank tonight. I just replaced the O-ring about 3 months ago so hopefully it is still reusable. I'll let you know what I find, I may be calling you for your spare sending unit.

Thanks,
Mike
 
Thanks JJ, I'll see if I have time to pull the unit out of the tank tonight. I just replaced the O-ring about 3 months ago so hopefully it is still reusable. I'll let you know what I find, I may be calling you for your spare sending unit.

Thanks,
Mike
 
Check the ground on the instrument. When the instrument has a bad / unreliable ground, it´ll show exactly the symptoms you mention. On the E3 where it (and the temp gauge, which can show the same behaviour) are srewed to a circuit board, the groundconnection, fed through the fastening screw can corrode and make the instruments "jumpy". Had it on all 3 E3s I´ve had. simply cleaning the connection and then carefully tightening the nut fixed it every time.
 
Check the ground on the instrument. When the instrument has a bad / unreliable ground, it´ll show exactly the symptoms you mention. On the E3 where it (and the temp gauge, which can show the same behaviour) are srewed to a circuit board, the groundconnection, fed through the fastening screw can corrode and make the instruments "jumpy". Had it on all 3 E3s I´ve had. simply cleaning the connection and then carefully tightening the nut fixed it every time.
 
The O-ring needs to be replaced when you pull the sender or you´ll have a gas leak that´s really annoying (smell mostly). The ring expands when it gets wet thorugh fuel and thereby seals. When you pull the sender and then put it back in, the seal will be pre-expanded and will not seal properly.
Alternatively, if you don´t have a new ring, clean the old one and let it sit dry, thus shrinking, for at least 48 hours.

At least that´s what the blue books say on the subject...
 
The O-ring needs to be replaced when you pull the sender or you´ll have a gas leak that´s really annoying (smell mostly). The ring expands when it gets wet thorugh fuel and thereby seals. When you pull the sender and then put it back in, the seal will be pre-expanded and will not seal properly.
Alternatively, if you don´t have a new ring, clean the old one and let it sit dry, thus shrinking, for at least 48 hours.

At least that´s what the blue books say on the subject...
 
hmmm

Jumpy gages are legendary in 2002s, of which I've had more than a dozen. the cure there is to run another ground from the back of the cluster to the body. Heck, the second ground should contact all gages.

A bad cluster ground may also manifest itself as poor illumination of the turn signal indicator

Well you could chase down and burnish the original ground, but it's simpler to add one. At least 2002 clusters come out of the dash easily, a philosophy to which our coupes most definitely do not subscribe.

I think you have an intermittent connection somewhere, and I'd look at the sender connections at the top of the sender, first. I DO NOT believe the sender works are at fault and I would not remove it without doing a fair number of other things first. That the gage registers correct, occasionally, proves that both wires on which the float rides, are intact. But you may have or be given other opinions, some of which are better than mine.
 
hmmm

Jumpy gages are legendary in 2002s, of which I've had more than a dozen. the cure there is to run another ground from the back of the cluster to the body. Heck, the second ground should contact all gages.

A bad cluster ground may also manifest itself as poor illumination of the turn signal indicator

Well you could chase down and burnish the original ground, but it's simpler to add one. At least 2002 clusters come out of the dash easily, a philosophy to which our coupes most definitely do not subscribe.

I think you have an intermittent connection somewhere, and I'd look at the sender connections at the top of the sender, first. I DO NOT believe the sender works are at fault and I would not remove it without doing a fair number of other things first. That the gage registers correct, occasionally, proves that both wires on which the float rides, are intact. But you may have or be given other opinions, some of which are better than mine.
 
Mike,

I did find my spare sender unit if you need it.

I will do some quick measurements to see what failure mode would cause the 1/15th reading and get back with my findings. My guess in an intermittently open sensor wire rather than an open ground might behave like you describe. I think the ground circuit is only part of the low fuel light circuit but I could be wrong.
 
Mike,

I did find my spare sender unit if you need it.

I will do some quick measurements to see what failure mode would cause the 1/15th reading and get back with my findings. My guess in an intermittently open sensor wire rather than an open ground might behave like you describe. I think the ground circuit is only part of the low fuel light circuit but I could be wrong.
 
Based on some testing, I would look for an open Level Sensor wire if not one of the items I mentioned. The Ground wire is purely cosmetic - the ground connection will be made metal on metal when the sensor is in the tank.

The circuit did work like I thought, basically the level sensor is about 5ohms to ground when full and 75ohms when empty. The low fuel signal is shorted to ground when the fuel is low. In order to see the needle jump to empty the Level Sensor path must be open circuited.

CoupeFuelSensor.jpg
 
Based on some testing, I would look for an open Level Sensor wire if not one of the items I mentioned. The Ground wire is purely cosmetic - the ground connection will be made metal on metal when the sensor is in the tank.

The circuit did work like I thought, basically the level sensor is about 5ohms to ground when full and 75ohms when empty. The low fuel signal is shorted to ground when the fuel is low. In order to see the needle jump to empty the Level Sensor path must be open circuited.

CoupeFuelSensor.jpg
 
JJ, Thank you for finding the sender. I have not had a chance to work on this and hope to dedicate some time on Sunday. If your sender works and you are willing to part with it, I wouldn't mind trying it as a process of elimination. I will also take the good advise from Tierfreund and Honolulu and look at the circuit board and the ground to see if they are culprit. I would like to pass along my thanks for the time and good advise, I really appreciate it.

Mike
 
JJ, Thank you for finding the sender. I have not had a chance to work on this and hope to dedicate some time on Sunday. If your sender works and you are willing to part with it, I wouldn't mind trying it as a process of elimination. I will also take the good advise from Tierfreund and Honolulu and look at the circuit board and the ground to see if they are culprit. I would like to pass along my thanks for the time and good advise, I really appreciate it.

Mike
 
temp gauge bounce

Not to hijack this thread, but every now and then my temp. gauge will decide to bounce a bit and then stay centered in the mid range. Anyone else experience with this?
 
temp gauge bounce

Not to hijack this thread, but every now and then my temp. gauge will decide to bounce a bit and then stay centered in the mid range. Anyone else experience with this?
 
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