Gas gauge doesn't go below 1/2. Fuel sender does not appear stuck.
 

From a full tank, it will go from full to 1/2 then stop.
Gas gauge doesn't go below 1/2.
I think once I get to low, a warning light goes on.

I pulled out the fuel sender and it didn't appear stuck.
The thin wire is smooth and not a hint of rust or corrosion.
The float moves up and down smoothly, the entire range.

What's the next step?

http://forums.pelicanparts.com/porsche-911-technical-forum/824804-fuel-gauge-ground.html

Check the ground located in the frunk adjacent to the fuse panel,
and, the connection (G) on the back of the gauge (Green wire).

Good luck,

Gerry

Does the level on the gauge drop if you firmly tap the gauge?

The next step is to see if the gauge shows less than 1/2 full if you manually slide the float down. I went thru this too, swapping in another used sender, keeping the same symptoms, many different gauges tried....turned out the fix was a brand new sender.

I had a similar problem with mine. I replaced the sender and that didn't fix it. I replaced the fuel gage and that didn't fix it. I removed the sender from the tank and reconnected the cable and checked manually and it worked perfectly. Put it back in the tank and it would hang up. I finally discovered that the tank top was slightly dented in, which changed the location of the sender at the bottom. When all the sender fasteners were tightened, the bottom of the sender was hitting against the tank back and binding the float movement. I had to make a half-moon shaped shim that fit over the mounting studs that I epoxied (JB Weld) to the tank top opening. The shim was installed at the front of the sender opening, which shifted the bottom of the sender forward. The sender rubber gasket sealed any small imperfections to the shim.

So, the first thing to do is remove the sender, reconnect the sender to see if the gage reads fully when shifting the float up and down. If that is OK, check the tank top.

If you have the sender out and the aluminum shroud removed you can connect all the wires, move the float up and down to the bottom and watch the gauge. Or have someone watch the gauge while you are doing it. That up and down movement should move the gauge needle continuously from full to empty. You can do the same with the sender out but completely assembled. Turn it right side up + Gauge on empty. Upside down = gauge on full. And with slow turning over any position in between. What has to happen is the the small slider contacts against the two wires make continuously good contact. Even if the wire seems OK poor contact of the slider contacts on the float could cause erratic gauge behavior.

I fixed my "79SC sender a couple of years ago. The float was frozen on the center slide rod and the wires covered with crud from old gasoline. After a good cleaning of all the elements the sender now works fine over the whole range with even the red light coming on when the tank is practically empty.

I had the exact problem, so I was going to suggest to remove the sender and... But you did that. I also did that and everything look OK.

The floater ride the wire with no problem when out side the tube but back in the tube it free fall one way but bind the other way. Took a look at the tube and it was slightly out of round. Roll it carefully like a cigar and it did the trick.

Gerry, I just cleaned the 2 frunk bay grounds when I did my headlight relays.

The gauge always works between F and 1/2 and then stops in the same place every time.
Would a bad connection at the gauge cause such a consistent behavior?

Thanks, I will remove the sender, move the float by hand,
and see if the gauge matches the float position.

Yes, a series resistance could give these symptoms.

pm me as needed.

I'm going with a bad sender. :) I have basically the same problem and after much testing, have decided that the sender is bad. The float moves freely up and down, grounds are good, other connections are good. I even get the idiot light.

Thanks for the suggestions.
I got motivated by all the replies and just got back from the garage.

Here is the deal.

The fuel sender float is not stuck.
It freely travels the entire length of the shaft.

Here is a video of me sliding the float between the top to the bottom a few times.
Notice the range of the fuel needle.
Even though the float is going to either extreme, the needle does not go much below half once the float is at the bottom.
I can live with this, and just need to remember that 1/2 really means 1/5, but am curious what causes this miscalibration.
Anyone have a friend who would actually just relabel "1/2" to "E" and black out the stuff below 1/2 ?

<iframe width="560" height="315" src="//www.youtube.com/embed/99TAb9jYsPY" frameborder="0" allowfullscreen></iframe>

Also, it's not like something is physically blocking the needle from going lower to the empty reading.
Note, when the ignition is off, the fuel needle rests at the very bottom.
http://i59.tinypic.com/5arofs.jpg

See what you got with the plug off and with the cable "jump". If you got "empty" and "full" (or vice versa), as per slodave: time for a new senders.

Well, let's try one more thing.

If you are brave enough, you can re-flow the solder joints in the gauge itself. It worked for me but later if came back. I had NoHo redo it properly and still I get false readings so yesterday I swapped the sender.

Old sender looked fine except a bit of residue on the float. Wires are so thin, how the heck can anyone really see if it is fouled? I must be getting old :eek:

If you do go with a new sender make sure you get a new rubber gasket.

Jim

JJ,
I'm not sure what the cable jump is.
Are you implying that even though the float freely travels from top to bottom, the sender might still be defective?

Draco,
Did your new sending unit fix the problem?
Looks like 90174180100 is about $150

Not sure, have to go empty to find out but it seems like it is.

Gauge is refurbed so all should be working now, I will know in a week or less.

I had exact same symptoms the re-flowing helped but was not permanent.

Jim

I went as far as taking my gauge apart. The needle moved through the arc just fine, when moving it by hand. No sticking spots. I took the sender out and manually tested it and watched the gauge. Needle would stick at certain points and would not really fall below half. TRE and I are on the same page about a failed sender. Kinda proven by the fact the idiot light does go on when nearly empty.

When you insert the sender does it go all the way down in the tank. I mean all the way down. if the tank is deformed at all the sender will bind as you tighten it down.

Sugarwood, this is a pretty good endorsement.

Do the swap and be done with it. Since you took it out, it isn't a big deal just do not over torque the nuts :-) 18 INCH/LB, star pattern.

Smear some gas on the new one so it will slip in nicely. Remember the new one will have a pin in it for shipping. Pretty obvious but you never know :confused:

It is actually an encapsulated sender the moving components are shielded, Yeah a dented up tank would cause problems if it hit the sender

I review my note (also amended my post for future search), it its exactly as per Jim said.

The floater work well outside the tube but bind when it it. Slightly out of round. I roll it slowly like a cigar and it did the trick.

I tested the resistance of my fuel sender.

On empty, it reads 67 ohms.
On full, it reads 2.7 ohms.

Does this mean the sender is good or bad?

Good.

Then it is most likely your gauge. remove and re-flow the solder joints and insure the terminals ar clean and tight. especially the ground

Ok, I'll try to pull the gas gauge.

The gauge works VERY consistently (from F to 1/2) and never flickers or jumps.
Wouldn't this mean it's not a connection or ground?

Is there a thread on how to resolder the gauge internals?

Yes, but while you are there take care if it all.

I'm having the exact problem, what was the fix?

Even though it's a 5 years old thread, I do remember what it was in my case.

The floater would jam at half way so it would never show full tank.

The tube was a bit out of round, so I roll it (very carefully) like a cigar and that fix it.

You can check this by taking the floater apparatus out (very fragile) and move the cork up and down along 2 thin wires on each side. The gauge should react accordingly.

As I documented in this thread, the sender float was not blocked. The video shows the gauge needle travel at both extremes of the sender float. The sender was not the problem, nor was mine out of round. Pretty sure I never replaced the sender.

The fuel sender worked fine when I removed and tested it.
I can tilt it in both directions, and it freely travels unobstructed.
It registers the proper resistance at both ends of travel. At the bottom it's 67. At the top it's 2.6
So, I was told the problem lies in the gauge itself.

<iframe width="560" height="315" src="//www.youtube.com/embed/RteD2y6xIy4" frameborder="0" allowfullscreen></iframe>

I have reused the gasket several times. No issue.
Mine was still perfectly rubbery as there is no heat like a crispy valve cover.
If there is no leak, opening it will not create one.
I had a spare on hand, but didn't use it since it was identically pliable to the replacement.
After a few more times of removing the sender, I used the new gasket, but really didn't need to.

I then hooked up a 5000 ohm potentiometer to verify the gauge worked fine.
Ok, I attached a 5000ohm potentiometer to the harness plug that the sender normally connects to.
In other words, the potentiometer is now replacing the fuel sender. It is not hooked directly to the gauges.
Recall, my fuel sender correctly sends 2.7 to 67 ohms. This poentiometer sends 2 to 5000 ohms.

Since it's 5000 ohms, when I calibrated the poentiometer to my multimeter, the slightest turn on the knob would put it past 100 ohms. Using the poentiometer in place of the sender, the gauge swept the entire E to F range. What does this tell us? My gauge goes below 1/2 and to E when there's a LOT of resistance (like 100's of ohms) but it seems the sender's 67 ohms is not cutting it.

<iframe width="560" height="315" src="//www.youtube.com/embed/gAcWvViDgJU" frameborder="0" allowfullscreen></iframe>[/QUOTE]

So, it seemed to be an issue of incorrect resistance being measured. I think I cleaned up the contacts at the fuel gauge itself and saw an improvement.
When I re-tested, the needle would drop to about 1/4 when the sender float bottoms out. That was close enough for me and I buttoned it back up.

To remove the gas gauge, first remove the adjacent gauge , and then push fuel gauge out from the hole next to it. Easier.

Here is some more fun reading, if inclined
http://forums.pelicanparts.com/porsche-911-technical-forum/847863-fuel-sender-fine-open-fuel-gauge-itself.html

I haven't inspected the gauge or it's connections yet.

"Bench testing" the sender gave me the same results. Full gauge with the float at the top (3.5 ohms) and half full with the float at the bottom (69 ohms).

Gauge reads empty with the sender disconnected.

Disassembled the sender and discovered the low fuel light switch is corroded and inoperable.

After cleaning the wires and re-staking the connections now the gauge will now read 1/4 tank when the float is at the bottom.

New sender delivered tomorrow (5/21), will post results.

Not to hijack someone else's thread, but, my 69 911 will register full, after 30ish miles it drops to 3/4, then quickly to almost empty. It sits there steady until I am almost empty. New fuel tank and sender. I took out the sender and hear it sliding freely. Idea's??

My clueless guess is that the new sender will also read 1/4.
Did you clean the contacts on the fuel gauge, or just the sender?

At the bottom it's 67.
At the top it's 2.6
Does that mean you're getting prematurely high resistance?
Did you clean the contacts on the fuel gauge ?

I agree but would like the low fuel light to operate.
I looked at the gauge and can see no corrosion, connectors good and tight.
I see a place for adjustment on the gauge, will try that after the sender is in.

Thanks for this post, I’ll be following along as I have a very similar problem.

I had the same problem where the gauge hung up at 1/2 tank. I replaced it with a new one from our host which worked like a champ for a few fill ups and now it hangs at 3/4 tank. Couple of questions:

Is it really safe to test the sender outside the tank with gas fumes coming out of the tank and the possibility of an arc from the sender?

If the sender worked at first and not now, should I just get another sender, or are there other fixes?

Quick,
The sender does not arc, but lay something over the gashole to feel safer.
That's weird that your replacement sender worked perfectly at first
That feels like it sort of rules out your fuel gauge contacts needing cleaning.
I guess I would test the sender and clean the gauge contacts anyway

Thanks for this advice. I cleaned up the terminals that connect to the sender (even though they were already pretty clean) but I didn’t check the gauge. I’ll get on it.

You could have a helper tilt the sender with wires still connected and view what happens on the gauge. Confirm the gauge shows 3/4 even when sender is at bottom of travel. Once that is confirmed, clean gauge contacts, and then perform the initial test again.

After I replaced the sender the gauge would go down to 1/4 tank but still not go any lower. I loosened what I thought was an adjustment on the back of the gauge, re-tightened and the gauge started working correctly. I feel like there was a poor connection inside the gauge.