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Fuel gauge calibration
Posted by: joelsplace ()
Date: September 05, 2018 02:50PM

Yes, Matt I know there are other threads on this but none of them I found address the real issue that all of my EMs have.
All of the EMs I've ever had Spyders and FCs too for that matter run out of gas between 1/8 and 1/4 tank showing on the gauge.
It isn't the sender.
I can pull the wire off and they read over full but when I ground the wire they read between 1/8 and 1/4 depending on the vehicle. I need to get the gauge working and then worry about the sender. I have a Spyder dash in front of me and it has a resistor on the back of the gauge. Do I need to add some resistance to it?

I saved an old rusty tank and cut the side out of it to do my sender calibration once I get the gauges working.

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Re: Fuel gauge calibration
Posted by: Brizo ()
Date: September 05, 2018 04:44PM

I've never tried to alter the gauge resistor but you may be able to "fine tune" it that way. Its a very delicate operation but I have bent the needle to get them to show empty.

Dan Brizendine,
'64 8door Greenbrier 140 PG. "In beautiful Wanamaker Indiana...with one stop light and 5 pizza shops"

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Re: Fuel gauge calibration
Posted by: 66vairman ()
Date: September 05, 2018 05:16PM

That's odd. I've worked on a number of cars with fuel gauge issues and rarely is the gauge a problem. Most of the issues are the sender, poor connections, and bad grounds. Although I've found bent needles when folks attempted to paint them.

The EM fuel gauge does have a resistor on the back that sometimes gets damaged, but it mainly affects readings above "E".

When you ground the sender input the one coil basically goes to ground and only the other coil is energized and pulls the needle to "E". If there is any resistance in the gauge input from the sender the gauge won't read empty.

I would suggest grounding the gauge at it's sender input terminal and if it goes to "E" then the wire from the tank has too much resistance or the tank sender is poorly grounded (the most common issue).

Let us know what you find.

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Re: Fuel gauge calibration
Posted by: 7004doorL ()
Date: September 05, 2018 07:17PM

If I could answer the Question:

Do I need to add some resistance to it?

IIRC some Dash Gauges like the Fuel Gauge are running off of 9 Volts provided by the vehicles's wiring. Corvairs and others.

So when you go out and try to start the car that has been sitting
the gas gauge reads correct even though there are not enough Volts to turn the Starter.

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Re: Fuel gauge calibration
Posted by: joelsplace ()
Date: September 05, 2018 08:13PM

The way I understand the fuel gauge works is it has one coil that constantly pulls it toward full and the other coil connected to the sender grounds pulls it toward empty. Apparently the coil connected to the sender isn't strong enough. It would be a good idea to check the wire from the gauge to the tank to see if it has too much resistance but I would think that when every EM/FC I've had has done it then it's more likely the gauge but I could be wrong and it is easy enough to check.
And no, the wiring provides 12V to the gauge. I've had people tell me they run off of 6V also. Maybe some did but not Corvairs. I've seen some old Chryslers and Fords on the internet that had voltage regulators to step down the voltage to the gauges.
Thanks!

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Re: Fuel gauge calibration
Posted by: MattNall ()
Date: September 05, 2018 08:27PM

Joel, the regulator it to keep the voltage at 12 VDC and not allow it to go higher...most any vehicle when running has over 13 volts in the system..

Get a simple regulator... '60 Chrysler Alt. Regulators used to be cheap!

[www.ebay.com]

Put it in the power lead for the gauge





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Fuel gauge calibration
Posted by: joelsplace ()
Date: September 05, 2018 08:55PM

So what is a regulator going to do for me Matt?

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Re: Fuel gauge calibration
Posted by: MattNall ()
Date: September 05, 2018 09:09PM

Should make the gauge more accurate... for a few busks...try it..

I've never seen your problem... everythin is just the opposite... Reads empty when 3-5gal. of the 14 are left!





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Fuel gauge calibration
Posted by: joelsplace ()
Date: September 05, 2018 09:25PM

That's odd. I've never seen an EM or FC that would read empty.

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Re: Fuel gauge calibration
Posted by: joelsplace ()
Date: September 05, 2018 10:00PM

I wouldn't think a VR would help anything since it has 2 coils working against each other. Wouldn't the voltage make the same difference on each coil and balance out?

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Re: Fuel gauge calibration
Posted by: JimBrandberg ()
Date: September 06, 2018 04:25AM

I daily drove several EMs into the ground and I went to E all the time. Not a Spyder though.

Jim Brandberg
Isanti, MN
CorvairRepair.com

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Re: Fuel gauge calibration
Posted by: 66vairman ()
Date: September 06, 2018 09:22AM

Matt - The GM Chevy Corvair gauges used a balanced bridge type of design so they are NOT affected by voltage fluctuations. Very reliable design.

The Ford products used a vibrating points regulator for only the gauges that are a simpler design. Worked fine until the regulator quit.

Joel - One thing I forgot to mention - some gauges have corroded contacts internally, especially the contact to the gauge case that grounds to the instrument bezel.

Usually not an issue out her in the West, but I did fix one with corrosion at the contact areas. Careful handling is required to dismantle and clean.

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Re: Fuel gauge calibration
Posted by: joelsplace ()
Date: September 06, 2018 09:57AM

I'll have to check that. Thanks!

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Re: Fuel gauge calibration
Posted by: joelsplace ()
Date: September 06, 2018 11:09AM

I took a spare Spyder fuel gauge apart and it is nice and clean inside. It has 2 coils that have tabs on top that reach out toward the mechanism on the needle. Both are bent at different angles that make one farther away from the needle than the other. I wonder if adjusting the bend will calibrate it?

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Re: Fuel gauge calibration
Posted by: joelsplace ()
Date: September 06, 2018 12:27PM

I've never followed the fuel gauge wire does it have a connector in the run somewhere? I would think that would be the likely suspect for high resistance.

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Re: Fuel gauge calibration
Posted by: jjohnsonjo ()
Date: September 06, 2018 02:24PM

[corvaircenter.com]


Schematic in your other thread, looks like only one connection.

J.O.

65 Corsa Turbo Vert
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Bethlehem,Pa

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Re: Fuel gauge calibration
Posted by: joelsplace ()
Date: September 06, 2018 02:37PM

I found it. There are 2 connectors between the dash harness and main harness under the dash speaker. One of them has the fuel gauge wire in it. I can't believe I haven't messed with that connector in all these years. Probably just forgot.
Thanks!

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Re: Fuel gauge calibration
Posted by: 66vairman ()
Date: September 07, 2018 10:05AM

joelsplace Wrote:
-------------------------------------------------------
> I took a spare Spyder fuel gauge apart and it is
> nice and clean inside. It has 2 coils that have
> tabs on top that reach out toward the mechanism on
> the needle. Both are bent at different angles
> that make one farther away from the needle than
> the other. I wonder if adjusting the bend will
> calibrate it?

joel - DO NOT start adjusting things until you determine if the gauge is the problem. Easy check - power to one terminal, ground to case, open input sender input terminal = "F" or more. Grounded sender input = "E". If that works your problem is in the wiring, grounds, or sender.

I've bench tested a number of gauges, mostly LM and rarely find a problem, mostly corrosion issues. Only a couple with "bent" needles from poor storage conditions.

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Re: Fuel gauge calibration
Posted by: joelsplace ()
Date: September 07, 2018 10:11AM

Yesterday I checked the spare I was messing with and it works fine. I'm wondering if all the ones I've messed with have high resistance in the connector between the dash harness and main harness.

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Re: Fuel gauge calibration
Posted by: 66vairman ()
Date: September 07, 2018 11:07AM

joelsplace Wrote:
-------------------------------------------------------
> Yesterday I checked the spare I was messing with
> and it works fine. I'm wondering if all the ones
> I've messed with have high resistance in the
> connector between the dash harness and main
> harness.

The range is 0 to 30 ohms. If you extrapolate a 1/8 increase in the gauge reading above normal would only be about 4 ohms. Corroded contacts (both supply and ground) can add that.

On old wiring when I clean the contacts I add a LITTLE di-electric grease before putting things back together. Works well EM turn signal/brake bulb sockets.

If the gauge works on the bench - it's not the gauge.

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