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7/21/15 9:42pm - Reply: 'Re: 1980 Fuel Gauge Calibrating'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19459
ebo said:We have a local quick stop fuel station that offers non ethanol fuel. I started running that in the vette last month. I filled the car 2 weeks before the gathering and it sat until that trip.
As we are on our way I noticed the gauge is reading full again, during the gathering there was no non ethanol fuel to find..... the gauge would not go all the way to full but very close. I came home close to empty and filled with the non ethanol and its back to the full mark on gauge.......doo doo doo doo
Evil Smileebo

Ethanol fuel is known to create issues with fuel senders, but since you just changed yours, I'd find it hard to believe it has already caused that problem. Plus...you had the same problem before.
If you still have your "old" sender, plug that thing in(be sure it is grounded to the car/chassis?, turn the key on, and move the float manually, and watch the gauge. See if it will go to full with the float lifted up, and go to empty all the way down.



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7/21/15 9:58pm - Reply: 'Re: 1980 Fuel Gauge Calibrating'
Sarge81 Lifetime Member
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WEST SENECA, NY - USA

Vette(s):
1981 Blue Ice Met. w/pearl ghost flames TKO500 5speed. LS1 Swap 3.45 Dana 44.

Joined: 12/3/2001
Posts: 2376
I checked our Supporting Vendors and Bair's has one listed for $95. He's the cheapest. Make sure you replace the gasket that goes in-between the sending unit and tank. I would also either replace or clean the filter socket (with solvent or carb cleaner) on the end of the pick up tube. 
You can also check out flea bay. They have reproduction units on there.

I'm not sure...but I may have the original one out of my '81 laying around. If I do I'll test it. It worked fine all the way until I removed it. I put a '82 sending unit in because it holds a in tank pump for fuel injection which my car now has. 


____________________________________

GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975




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7/22/15 12:30pm - Reply: 'Re: 1980 Fuel Gauge Calibrating'
my80Vette
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Dacula, GA - USA

Vette(s):
1980 Corvette White and Black with Black interior. 350 V-8 Auto

Joined: 7/18/2015
Posts: 32
Thanks fir the info. Let me know if you have the old one available please
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7/23/15 4:44am - Reply: 'Re: 1980 Fuel Gauge Calibrating'
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Bellingham, MA - USA

Vette(s):
1980 loaded red on red. 68,000 original miles. Second owner. Well documented with all original paperwork. NCRS Founders Award 9/27/14. NCRS Top Flight 10/12/14.

Joined: 6/23/2014
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7/23/15 1:05pm - Reply: 'Re: 1980 Fuel Gauge Calibrating'
kstyer Lifetime Member
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CUYAHOGA FALLS, OH - USA

Vette(s):
1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!

Joined: 12/2/2003
Posts: 6410
EBO,  your fuel was partly shorting your sending unit resistor.  Remember, grounded is empty.  When the fuel was below the level, it was no longer shorted.
The odd part is that you had enough ethanol to create that conductivity on the sensor resistor.   Normally that won't happen.   C3s should not have more than 10% ethanol.  I highly suspect the fuel was 15%  or more.   Lucky it did not damage other parts of the system.


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On the "Tail of the Dragon"
(some day, no strike that, October 2008 it turned red, still in progress!)

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7/23/15 1:13pm - Reply: 'Re: 1980 Fuel Gauge Calibrating'
kstyer Lifetime Member
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CUYAHOGA FALLS, OH - USA

Vette(s):
1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!

Joined: 12/2/2003
Posts: 6410
You should give Bairs a try for the unit.   They are one of our sponsers.
 
EBO,  Your fuel was partly shorting the sending unit.  Remember, when grounded the gauge reads empty.  When the fuel level dropped, the now dry sending unit resistor worked properly again.
 
What suprises me was that your fuel had enough ethanol to do that.   Our C3s are only designed to handle 10% ethanol.  My guess is you had 15% or more.  (the worst I have seen when the pump said 10 or 12% was over 40%)  You are lucky it did not damage other fuel system components.


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On the "Tail of the Dragon"
(some day, no strike that, October 2008 it turned red, still in progress!)

(click either image to see a bigger version)
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7/24/15 9:34am - Reply: 'Re: 1980 Fuel Gauge Calibrating'
Sarge81 Lifetime Member
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WEST SENECA, NY - USA

Vette(s):
1981 Blue Ice Met. w/pearl ghost flames TKO500 5speed. LS1 Swap 3.45 Dana 44.

Joined: 12/3/2001
Posts: 2376
my80Vette said: Thanks fir the info. Let me know if you have the old one available please

I'll get back to you Monday and let you know if it's still around. I'm at "Ebo's" for the"Eboland" party rest of the week. Big smileParty



____________________________________

GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975




Click here to see more pics of my Vette on CarDomain.


Lifetime Member #26
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7/28/15 9:27am - Reply: 'Re: 1980 Fuel Gauge Calibrating'
my80Vette
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Dacula, GA - USA

Vette(s):
1980 Corvette White and Black with Black interior. 350 V-8 Auto

Joined: 7/18/2015
Posts: 32
Sarge81 said:
my80Vette said: Thanks fir the info. Let me know if you have the old one available please

I'll get back to you Monday and let you know if it's still around. I'm at "Ebo's" for the"Eboland" party rest of the week. Big smileParty




Hey Sarge I hope you had a good weekend at Eboland. Where you able to find the old sending unit and if so what do you want for it. Thanks
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7/28/15 3:59pm - Reply: 'Re: 1980 Fuel Gauge Calibrating'
kstyer Lifetime Member
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CUYAHOGA FALLS, OH - USA

Vette(s):
1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!

Joined: 12/2/2003
Posts: 6410
Ebo, as already stated the percentage of ground is what determines the fuel gauge reading.  Our cars were made to handle up to 10% ethanol.  Many gas station pumps are now 12 to 15%, even if they say 10%.   The feds made this change allowable several years ago.   The GM owners manuals used to say 10% and the Feds required a recall to "correct" the issue.   GM simply did a recall to the owners manual.  They replaced the page with one that said 12%.
 
Different fuel compositions change the fuel conductivity.  There are acutally electronic tools that use resistance to determine ethanol content.   The ethanol is making the fuel sending unit more conductive, increasing the ground path, causing a reading lower than it would be otherwise.  Without the ethanol, the resistance is normal, and the gauge reads properly ( or close to it ).
 
Keep in mind other factors tie into this.  Fuel is custom blended on average every 3 weeks to adapt for changing climate.  This includes temperature, altitude, humidity, and other factors.   So different areas of the country may cause this problem, and others not.  Different times of the year can also have an effect.  AND different units can be affected differently with the same blends.   Quite a odd blend of chemical and mechanical soup.
 
The EPA uses Indolene instead of gasoline to do all emission testing on new cars in controlled conditions to determine emissions and mileage.  This keeps a fair compairison of all vehicles without variations due to different fuels.


____________________________________
On the "Tail of the Dragon"
(some day, no strike that, October 2008 it turned red, still in progress!)

(click either image to see a bigger version)
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7/28/15 7:10pm - Reply: 'Re: 1980 Fuel Gauge Calibrating'
Sarge81 Lifetime Member
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WEST SENECA, NY - USA

Vette(s):
1981 Blue Ice Met. w/pearl ghost flames TKO500 5speed. LS1 Swap 3.45 Dana 44.

Joined: 12/3/2001
Posts: 2376
my80Vette said:
Sarge81 said:
my80Vette said: Thanks fir the info. Let me know if you have the old one available please

I'll get back to you Monday and let you know if it's still around. I'm at "Ebo's" for the"Eboland" party rest of the week. Big smileParty




Hey Sarge I hope you had a good weekend at Eboland. Where you able to find the old sending unit and if so what do you want for it. Thanks

Hi Mitch, yup we had a blast at Eboland. Lots of good food, drink and adventures with a couple tech/repair sessions. I finally made it over to the shop today. Unfortunately the sending unit got tossed. Sorry I couldn't help you out. Unhappy



____________________________________

GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975




Click here to see more pics of my Vette on CarDomain.


Lifetime Member #26
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7/28/15 7:15pm - Reply: 'Re: 1980 Fuel Gauge Calibrating'
my80Vette
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Dacula, GA - USA

Vette(s):
1980 Corvette White and Black with Black interior. 350 V-8 Auto

Joined: 7/18/2015
Posts: 32
Sarge81 said:
my80Vette said:
Sarge81 said:
my80Vette said: Thanks fir the info. Let me know if you have the old one available please

I'll get back to you Monday and let you know if it's still around. I'm at "Ebo's" for the"Eboland" party rest of the week. Big smileParty




Hey Sarge I hope you had a good weekend at Eboland. Where you able to find the old sending unit and if so what do you want for it. Thanks

Hi Mitch, yup we had a blast at Eboland. Lots of good food, drink and adventures with a couple tech/repair sessions. I finally made it over to the shop today. Unfortunately the sending unit got tossed. Sorry I couldn't help you out. Unhappy




Thanks for checking. I think I'm going to try to take it apart and clean it first. If that doesn't work I'll call Bairs.
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8/10/15 8:09pm - Reply: 'Re: 1980 Fuel Gauge Calibrating'
my80Vette
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Dacula, GA - USA

Vette(s):
1980 Corvette White and Black with Black interior. 350 V-8 Auto

Joined: 7/18/2015
Posts: 32
Just thought I let people know that Bairs doesn't carry the fuel sending unit anymore. They said they had too many problems with them. I did take mine apart today to try to clean it but that turned out to be just a waste of a couple hours:) I'll be ordering one shortly.
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