Wonky Fuel Level

[Porsche904Guy]

Hi Everyone,

Picked up a 1979 911SC with a 3.2 in it. Fuel gauge was always maxed out regardless of level, so I figured I'd throw in a new sender since they are cheap.

Now the fuel gauge will move a bit here or there, but is still incredibly inaccurate. Reads almost empty on a full tank, and will move up as some gas gets used up.

Does this suggest an issue with the gauge, or do I need to troubleshoot wiring?

[PeteKz]

Possibly gauge, more likely grounds. Pull the gauge out and loosen, wiggle and tighten the wires on the back of it. Check that the ground wire is also well grounded on the chassis. If you ground the green wire to the sender, the gauge should go to max.

[snbush67]

The float in the sender has to travel smoothly. The tube that it travels in has to be perfect. You might have to futz with it. If it’s not the grounds it’s likely the float.

[chuckr]

I had similar issues with my fuel sender, ordered new aftermarket sender, yea, pretty cheap for a Porsche part. It started giving me bad readings after about 6 months, ordered another one, same kind, been working fine.

[Ian Comerford]

Originally Posted by snbush67

The float in the sender has to travel smoothly. The tube that it travels in has to be perfect. You might have to futz with it. If it’s not the grounds it’s likely the float.

I have experienced this a couple of times over the years. If you remove the sender from the tank and then remove the tube you may find that the rod on which the float travels is tarnished which causes the float to stickm8n certain positions. Some fine metal polish easily removes the tarnishing and allows the sender to do its job again.

[Porsche904Guy]

Originally Posted by Ian Comerford

I have experienced this a couple of times over the years. If you remove the sender from the tank and then remove the tube you may find that the rod on which the float travels is tarnished which causes the float to stickm8n certain positions. Some fine metal polish easily removes the tarnishing and allows the sender to do its job again.

Yes, but installed a new sender which moved the gauge, but still totally inaccurate.

Swapped a gauge from anther car, moved the needle again but still inaccurate (reads half full on full tank).

I guess it is something in the wiring.

[snbush67]

Originally Posted by Porsche904Guy

Yes, but installed a new sender which moved the gauge, but still totally inaccurate.

Swapped a gauge from anther car, moved the needle again but still inaccurate (reads half full on full tank).

I guess it is something in the wiring.

Doesn’t matter, you have to make sure the float is traveling free. The gauge doesn’t care if the sender is old or new, only that it’s traveling smoothly.

[Porsche904Guy]

Originally Posted by snbush67

Doesn’t matter, you have to make sure the float is traveling free. The gauge doesn’t care if the sender is old or new, only that it’s traveling smoothly.

Well, just because the parts are new doesn't mean they work properly.

Took the old sender and was able to notice float moving freely. Hooked it up to test, and now appears to be working well.

The float from the new sender I had put in did not feel like it was moving freely. I guess I'll try to return it.
https://www.pelicanparts.com/More_Info/90174180100.htm?pn=901-741-801-00-M350&bc=c&SVSVSI=0568

[snbush67]

Originally Posted by Porsche904Guy

Well, just because the parts are new doesn't mean they work properly.

Took the old sender and was able to notice float moving freely. Hooked it up to test, and now appears to be working well.

The float from the new sender I had put in did not feel like it was moving freely. I guess I'll try to return it.
https://www.pelicanparts.com/More_Info/90174180100.htm?pn=901-741-801-00-M350&bc=c&SVSVSI=0568

Great follow up. Glad you got it fixed!